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Transparency and Alpha Channels: The Definitive Guide

Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
01-04-2006 18:57
FREQUENTLY ASKED QUESTIONS ABOUT TRANSPARENCY

The most frequently asked question in the texturing forum is “How do I create transparency with alpha channels?” so if you’re wondering, you’re certainly not alone. I’ve answered the question for people hundreds of times here over the past 2 years.

As regular visitors to this forum are aware, I’ve got a standardized explanation of what channels are and how they work, as well as several tutorials for various software, which I routinely paste into relevant threads whenever the question comes up. I’ve decided to expand on the explanatory info with a little more detail in FAQ format, and to paste all the tutorials into a single thread.

I’ve tried to make this as layman-friendly as possible while still containing a lot of useful information. This should be the definitive resource for anyone with a question on how channels work, what they do, and more specifically, how to create and use alpha channels for transparency.

This first section contains frequently asked questions about channels in general, non-specific to any particular software but common to them all. The FAQ section discusses governing principles of color screen imagery, and thus is applicable as general knowledge that will be beneficial to anyone using any graphics software for any purpose.

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How do I give my image a transparent background?


Transparency in SL textures is defined by an image element called an alpha channel. In order for transparency to exist in an image, it must contain this element. This guide is loaded with information on what alpha channels are, how they work, and how to create them. Read on.


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What are alpha channels?


Simply put, an alpha channel is a data map embedded into an image that contains information about a certain aspect of the image other than color. For SL purposes, an alpha channel can be defined even more simply as a transparency map. Strictly speaking, alpha channels can contain information about all kinds of image aspects besides just transparency, but transparency is the only one SL can use. For more on what that means, read the sections below, entitled "Color Space & Channels" and "Channels & Transparency". For help with creating and using alpha channels, this guide is loaded with info. Keep reading.


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How come the transparent areas of my image appear white in SL instead of transparent?


If this is happening, it's because your image contains no alpha channel. Whithout the alpha channel present, SL has no way of determining which pixels are supposed to be transparent since the alpha channel is what contains all the transparency data. Without it, the only data present in the image is color data. Since the "transparent" pixels have no color, SL interprets them as white. To solve the problem, make sure your image contains an alpha channel, and that you've saved it as 32-bit TGA.

This guide contains a ton of information on what alpha channels are, how they work, and how to make them, so keep reading.


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Color Space & Channels – What are they?

Images designed to be shown on a color screen exist in what as known as RGB color space, meaning they are comprised of the three primary colors, red, green, & blue. The relative brightness of each of these primary colors in each pixel determines each pixel's actual color. For example, a pixel comprised of equal values of red and blue without any green would appear to be purple. A pixel comprised of maximum values of all 3 colors would appear to be white.

Under the RGB color space model, there are 256 available shades for each of the 3 primary colors. These shades are calculated as numerical values ranging from 0 to 255. Since there are 3 colors in use, and 256 possible values for each, the total number of colors available in RGB color space comes to about 16.7 million colors (256 x 256 x 256 = 16,777,216).

Okay, so what do all those numbers mean to us as artists? Well, the answer, thankfully, is we don’t really have to deal with them as numbers. GUI designers long ago came up with a system by which we can use our intuitive visual skills to “see” what’s happening in an image without having to do any arithmetic. Here’s how it works.

When taken separately, the individual mathematical values for red, green, or blue in each pixel are represented by specific shades of gray, ranging from black, which represents zero, to white, which represents 255. Under this system, all the representative pixels together form a grayscale image called a channel. Each channel is basically a data map which governs, pixel by pixel, the amount of its representative color that is present in the image.

Every RGB image has a channel that governs red, a channel that governs green, and a channel that governs blue. In each individual channel, white represents the maximum possible concentration of color and black represents the absence of color. Shades of gray represent amounts of color that are less than the maximum. The darker the gray, the lesser the concentration of color. The lighter the gray, the more color is present.


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Channels & Transparency – What do Alpha Channels do?


All RGB color images start with the same 3 primary color channels described above, but images can also contain additional channels that govern other attributes such as transparency, bumpiness, shininess, etc. These additional channels are called “alpha channels”.

Alpha channels can have many functions, but most of them are beyond the scope of this discussion for SL purposes. Therefore, all mention of alphas in this guide from this point on will be in reference to how they govern transparency.

Again, images that have transparency start with the three primary color channels, but also have a fourth channel, called Alpha, which represents opacity. They therefore exist in what is called RGBA color space, obvious extension of RGB. For RGBA images, white in the alpha channel represents complete opacity and black represents the absence of opacity (transparency). Shades of gray represent semi-transparency. The darker the gray, the more transparent. The lighter the gray, the more opaque.

So, for example, if you are making a bikini top for your avatar, the alpha channel would be white in the shape of the bikini top, and black everywhere else. The white part makes the bikini top 100% opaque so that you won't be able to see through it when it's on the av, and the black part makes the rest of the image invisible so that there appears to be nothing on the av's arms, stomach, etc.


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How do I make alpha channels?

Below the FAQ section is a tutorial section with specific instructions for creating alpha channels in Photoshop, Photoshop Elements, and Paint Shop Pro.

I’m also working on a GIMP tutorial, but I haven’t finished it to my satisfaction yet since I’m still learning the program myself. I want to make sure I really know what I’m talking about before I publish. In the mean time, I recommend the GIMPshop plug-in which changes GIMP so it acts more like Photoshop. This will allow Photoshop tutorials to be useful for GIMP users.


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How do I make part or all of an image translucent, as opposed to fully transparent?


Areas of an image that are semi-transparent should be gray in the alpha channel. As described above, the darker the gray you use in the alpha channel, the more see-through the corresponding part of the image will be. The lighter the gray, the more opaque.

For example, a piece of frosted glass would require a very light gray in the alpha channel. Frosted glass is almost opaque, so the alpha should be almost white.

Something like a pair of nylon stockings would be in the medium gray range. Stockings are generally transparent enough that you can see the skin underneath them, but not so transparent that the stocking material itself isn't readily noticeable. They're about half way between transparent and opaque, so their gray value on the alpha channel would be about half way between black and white, medium gray.

Water would fall into the dark gray range. Water is very see-through, but not completely invisible. It's mostly transparent, so it's gray value on the alpha channel would be mostly black.

Just as a reminder, note that none of the grays in any of these examples affect the color of the image in any way. Alpha channels only govern transparency, not color.



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Why TGA?


TGA, or Targa format, is the most commonly used image format for texturing for 3D applications. It has certain advantages for this purpose over other formats, among them being it is lossless, it has an entirely predictable file size, and its simple bitmap formatting is very easy for almost all programs to interpret. Of the 3 formats SL will accept, it is the only one that supports transparency.


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What about JPEG and BMP


JPEG and BMP are poor image format choices for 3D applications. Using them is ill advised for a number of reasons, but for this discussion, the fact that they do not support transparency is enough. As I always say, use TGA, everyday, all the way, TGA.


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What’s the deal with JPEG2000?


JPEG2000 (not to be confused with JPEG) is the image format that SL uses internally. All images that are uploaded to SL are converted to JPEG2000 by the SL client at the time of upload. While programs like Photoshop can certainly create JPEG2000’s, SL can only use the ones it creates itself. It cannot import JPEG2000’s from anywhere else. Once again, TGA is the format to use. Stick with TGA on your end, and let SL worry about the conversion.


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What’s the difference between 24-bit and 32-bit TGA?


As was mentioned above, color images for the screen are comprised of 3 primary color channels. Each of these channels constitutes 8 bits of data per pixel. Since there are 3 channels, color images are 24-bit.

Images with transparency contain a 4th channel, called alpha, which adds another 8 bits, bringing the total to 32. Therefore, images with transparency are 32-bit.

It’s a common misconception among those new to digital art that more bits must somehow be better than less bits, and they end up saving everything as 32-bit. This is a big mistake. Only images that need transparency should ever be saved as 32-bit. Fully opaque images should always be saved as 24-bit. Using 32-bit unnecessarily increases an image’s file size by 33%, and can cause display problems. See the next question for more on this.


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Why do sections of images sometimes disappear or seem to change position in SL?


This phenomenon has to do with a glitch common to nearly all 3D applications in what’s known as alpha sorting. It happens in nearly all video games, and even in high end 3D modeling packages costing thousands of dollars. What happens is when two or more 32-bit images are placed so that they intersect or overlap in close proximity, the renderer has trouble determining which one to draw first. As a result, the images can appear to flip-flop their positions in 3D space, to cancel each other out, or to otherwise behave strangely.

The way to cut down on this is to make sure that 32-bit images are only used when absolutely necessary. Images that do not need transparency should always be saved as 24-bit. Beyond that, there are certain building techniques in SL that can minimize the effect, and others that actually take advantage of it, but building is beyond the scope of this guide. There are plenty of tips about this on the building forum.


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Why do I see a white halo around my partially transparent images in SL?


This is a very common problem caused by what’s know as anti-aliasing, which is the computer’s way of smoothing the appearance jagged edges by combining colors along diagonals or curves lines. Just like with any other image element, the pixels where black meets white in alpha channels get anti-aliased so that they appear to blend smoothly together. This anti-aliasing results in gray pixels, which end up translating to a semi-transparent outline around the opaque parts of the image.

How this results in a white halo is pretty simple. If there’s white space (or blank space) surrounding the opaque parts of your image, those anti-aliased, semi-transparent edge pixels end up combining their coloring with the white around them. They become so lightened by the process that they appear to be a halo.

The way to avoid the halo ranges from very, very simple to slightly complicated. The simplest thing to do is just to give your images a dark background. Technically this gives you a dark halo instead of a light one, but dark halos are usually undetectable in SL. Most of my tutorials include this method, since it’s the easiest to explain, and the most universally applicable for all situations.

Other methods include bleeding the coloring of the opaque areas into the transparent areas. This is visually superior to the dark background method, but a little more complicated to do. Photoshop users may wish to view Robin Sojourner’s wonderful video tutorial at http://www.robinwood.com/Catalog/Technical/SL-Tuts/SLPages/SLTranspStart.html , showing how she eliminates the halo by using a Gaussian blur filter. There are also 3rd party plug-ins for Photoshop that can be useful for this, my favorite of which is a filter from Flaming Pear called Solidify. At the time of this publication, Solidify is available for free on Flaming Pear’s website in their Free Plugins pachage. http://www.flamingpear.com/download.html


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What about automated alpha channel plug-ins? I’ve seen one for Photoshop mentioned on this forum. Does it work?


The file in question is actually the TGA saver plug-in from Photoshop 7.0, which was Adobe’s one and only experiment with automated alpha channel creation for TGA. The experiment was a dismal failure, riddled with problems. Adobe quickly realized they had made a monumental mistake with 7.0, and they patched it with version 7.0.1, which got rid of the automation and the problems that went with it.

However, some people unfortunately are still under the impression that the automation is a time-saver, and they use that plug-in from 7.0 to alter the way other versions of Photoshop operate. In truth, people who use it are actually making things much harder on themselves without even realizing it. Let me explain.

Files created with the PS 7.0 TGA saver utility suffer the following problems:

1. They will have visual artifacts in them which will be impossible to correct, the most common of which is a white halo surrounding the opaque parts of the image.

2. The image files will be incompatible with most graphics applications. Instead of real alpha channels, which have been a staple of the graphics industry for decades, and so can be understood by nearly all graphics programs, those 7.0-style files contain a proprietary element called an "embedded alpha", which almost no program on Earth can read. It's only by an utter miracle of conicidental timing that SL can read those files at all. The relevant part of SL happened to have been under development at during that short 3-month period when PS 7.0 was current.

3. People who use the embedded alpha work flow do so primarily because they mistakenly think it's a time saver. In truth, it is not a significant time saver at all since making an alpha channel only takes a few seconds at most. Learning to use alpha channels might not be intuitive for most people at first, but really, once you learn how to do it, it's incredibly quick and easy. It's not rocket science.

4. For images with complicated transparency levels, like stained glass windows, for example, the embedded alpha work flow actually makes the process take MUCH longer than it takes to make a real alpha channel.

5. Very importantly, embedded alpha work flow encourages destructive habits. By disallowing you the ability to create and edit alpha channels properly, it ends up costing you an enormous amount of control and flexibility. There are countless situations in which working directly on the alpha channel itself allows you to do things you could never otherwise do in any reasonable amount of time, if at all.

6. Once installed, that 7.0 plugin effectively destroys your ability ever again to work properly with real alpha channels should you ever choose to do so. Even if you remove it, PS won't behave entirely properly afterwards. The only recourse is to completely uninstall PS and then reinstall it all over again. What a pain.

7. Files containing embedded alphas are prone to sudden, irreversible data corruption. I have no idea why, but they often end up with colored lines spontaneously appearing across any white space in the image. Once that happens, the file is toast. You can manually erase the lines, but as soon as you close the file and reopen it, they come back.


In short, embedded alpha automation is bad news. Don’t use it. Read this guide, and learn to make proper alpha channels yourself.



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I’ve heard Photoshop 7.0 is bugged, and that it handles transparency differently than all other versions of Photoshop. Is this true?


Yes, it’s true. Anyone using 7.0 should download the free 7.0.1 update from Adobe before proceeding any further. See the previous question for the biggest reason why.



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Further Information
Robin Sojourner has kindly put together a more visualized explanation on her website of many of the concepts explained above. It's well worth taking looking at.

http://www.robinwood.com/Catalog/Technical/SL-Tuts/SLPages/AChannelDiscover1.html

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Land now available for rent in Indigo. Low rates. Quiet, low-lag mainland sim with good neighbors. IM me in-world if you're interested.
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
Transparency and Alpha Channels: The Definitive Guide
01-04-2006 18:58
TUTORIALS

This section includes specific tutorials for creating alpha channels in various software including Photoshop, Photoshop Elements, and Paint Shop Pro (GIMP tutorial coming soon). If you haven’t already done so, I recommend reading the FAQ section before proceeding to the tutorials. Understanding the WHY behind what you’re doing always makes learning the HOW a lot easier.

For instructions for your program of choice, simply scroll down to it and follow the instructions. I’ll be sticking with the example of a bikini top in each one.

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Adobe Photoshop


In Photoshop, there are many ways to perform any given task, and alpha channel creation is certainly no exception. The first tutorial, dubbed “Method 1”, is the one I’ve been pasting into threads on this forum since day one. I prefer it as a teaching tool since I feel it helps the user best understand the process of what’s happening. It’s not exactly the fastest though, so more advanced users may prefer Methods 2 or 3. Method 4, which I've dubbed "The 2-Second Method" is by far the fastest and simplest, consisting only of essential operations. Below the written tutorials, I've also included a link to Robin Sojourner's tutorial video on her website, another really great learning tool.

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Adobe Photoshop – Method 1


As mentioned above, this is my preferred method for new users to learn with.


1. On the Layers Palette turn off all layers except for the layer that has your bikini on it. (To turn a layer off, click the eyeball symbol to the left of its name.)


2. If the bikini layer has any white space around the bikini itself, use the eraser to get rid of the white space. It's very important at this stage that the bikini be on its own layer with nothing else on it. (NOTE: There are much better tools available than the eraser for this purpose. For the sake of simplicity in the tutorial, the eraser just happens to be the quickest one to talk about.)


3. On the Layers Palette, ctrl-click the thumbnail for the layer with the bikini on it. (The thumbnail is the little picture of the layer directly to the left of the layer's name.) This will select everything on the layer. You should see the "marching ants" outlining your bikini now. If there are elements of the bikini on any other layers, hold down shift, and then ctrl-click their respective thumbnails to add them to the selection. Make sure not to include the background or any of the template layers.


4. On the Layers Palette, click the tab that says Channels to switch it to the Channels Palette. What you should see listed here are the three primary channels for your image, labeled, "Red", "Green", & "Blue", and a master channel for the three, labeled "RGB". If you see any other channels besides those four, delete them now.


5. In the lower right corner of the Palette Window, locate the button that looks like a square sticker being peeled from its backing. It's the second one from the right. It's immediately to the left of the one that looks like a trash can. It says "New Channel" when you hover your mouse over it. Click it.


6. You should now see a new channel called "Alpha 1", which is currently all black. Make sure all channels except for Alpha 1 are turned off and that Alpha 1 is turned on. This should have happened automatically when you created Alpha 1, but if it didn't, do it now.


7. Your canvas should now appear to be solid black with the exception that you should still be able to see the "marching ants" outline of your bikini. Paint everything inside the outline white and leave everything outside of it black.


8. Click "Select" on the menu bar at the top of the screen to pull down the Select Menu. Click "Deselect" and you should see the marching ants disappear.


9. OPTIONAL STEP: "DEHALOING" - On the Channels Palette, turn the red, green, & blue channels back on, and turn Alpha 1 off. Now click the tab that says layers to switch back to the Layers Palette. Create a new layer by pressing the same button you previously used to create the new channel. (Just as it created a new channel while you were on the Channels Palette, it will create a new layer while you're on the Layers Palette.) Click on the name of this new layer and drag it underneath the layer with the bikini on it. Paint the new layer 50% gray or darker; black is fine. (The gray/black layer will prevent the white halo sometimes caused when Alphas are created the way we just did it. If you don't know what I mean by that, don't worry about. Just make sure to always put a gray/black layer underneath your work and you'll never have to see that white halo. Alternatively, more advanced users may wish to use one of the better halo-elimination methods discussed in the FAQ.)


10. Save your file as a 32-bit TGA and upload it to SL.



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Adobe Photoshop – Method 2


This differs from the method above in that it employs the use of the “Save Selection As Channel” function to eliminate the step of hand-painting the alpha channel. This is a slight time saver.


1. On the Layers Palette turn off all layers except for the layer that has your bikini on it. (To turn a layer off, click the eyeball symbol to the left of its name.)


2. If the bikini layer has any white space around the bikini itself, use the eraser to get rid of the white space. It's very important at this stage that the bikini be on its own layer with nothing else on it. (NOTE: There are much better tools available than the eraser for this purpose. For the sake of simplicity in the tutorial, the eraser just happens to be the quickest one to talk about.)


3. On the Layers Palette, ctrl-click the thumbnail for the layer with the bikini on it. (The thumbnail is the little picture of the layer directly to the left of the layer's name.) This will select everything on the layer. You should see the "marching ants" outlining your bikini now. If there are elements of the bikini on any other layers, hold down shift, and then ctrl-click their respective thumbnails to add them to the selection. Make sure not to include the background or any of the template layers.


4. On the Layers Palette, click the tab that says Channels to switch it to the Channels Palette. What you should see listed here are the three primary channels for your image, labeled, "Red", "Green", & "Blue", and a master channel for the three, labeled "RGB". If you see any other channels besides those four, delete them now.


5. At the bottom of the Palette Window, locate the button that looks like a rectangle with a circle in the middle. It's the second one from the left. It says "Save Selection as Channel" when you hover your mouse over it. Click it.


6. You should now see a new channel called "Alpha 1", which is white inside the selection marquee, and black all around it. By default, this channel will have its visibility turned off. This is fine. The image will behave exactly the same in the end whether it’s on or off. If you want to look at your new alpha channel, just turn it on and turn RGB off.


7. Click "Select" on the menu bar at the top of the screen to pull down the Select Menu. Click "Deselect" and you should see the marching ants disappear.


8. OPTIONAL STEP: "DEHALOING" - On the Channels Palette, turn the red, green, & blue channels back on, and turn Alpha 1 off. Now click the tab that says layers to switch back to the Layers Palette. Create a new layer by pressing the same button you previously used to create the new channel. (Just as it created a new channel while you were on the Channels Palette, it will create a new layer while you're on the Layers Palette.) Click on the name of this new layer and drag it underneath the layer with the bikini on it. Paint the new layer 50% gray or darker; black is fine. (The gray/black layer will prevent the white halo sometimes caused when Alphas are created the way we just did it. If you don't know what I mean by that, don't worry about. Just make sure to always put a gray/black layer underneath your work and you'll never have to see that white halo. Alternatively, more advanced users may wish to use one of the better halo-elimination methods discussed in the FAQ.)


9. Save your file as a 32-bit TGA and upload it to SL.


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Adobe Photoshop – Method 3


This method differs from the two above in that it employs the use of layer groups and masks to give alpha channel creation a little bit more of a “what you see is what you get” feel. A mask is basically an embedded element inside an image that attaches to a layer or set of layers and behaves very similarly to how alpha channels behave. Using them takes slightly longer, but some people find this method to be a little more intuitive than the previous two.



1. If the layer with the bikini top on it has any white space around the bikini itself, use the eraser to get rid of the white space. It's very important at this stage that the bikini be on its own layer with nothing else on it. (NOTE: There are much better tools available than the eraser for this purpose. For the sake of simplicity in the tutorial, the eraser just happens to be the quickest one to talk about.)


2. On the Layers Palette, link all layers. Do this by clicking in the little blank square next in between each layers thumbnail and its eyeball symbol. You’ll see a little chain-link icon appear in each box.


3. On the Layer Menu at the top of the screen, go Layer -> New -> Layer Set From Linked. You should now have a new layer set with all your layers inside it. By default, the set should be open so you can see all the layers it contains listed below it, but if it’s closed open it now by clicking on the little triangle icon to the left of the folder icon. The folder icon is directly to the left of the layer set’s name. When you click the triangle, you’ll see it rotate 90 degrees as the set’s contents appear & disappear. Make sure it’s pointing down and that all layer names are visible.


4. On the Layers Palette, ctrl-click the thumbnail for the layer with the bikini on it. (The thumbnail is the little picture of the layer directly to the left of the layer's name.) This will select everything on the layer. You should see the "marching ants" outlining your bikini now. If there are elements of the bikini on any other layers, hold down shift, and then ctrl-click their respective thumbnails to add them to the selection. Make sure not to include the background or any of the template layers.


5. On the Layers Palette, click on the name of the layer set. You should still see the marching ants around the bikini at this point, by the way, since we haven’t deselected anything yet.
Now locate button at the bottom of the Layers Palette that looks like a gray rectangle with a white circle in the middle. It’s the one that says “Add Layer Mask” when you hover the mouse over it. Click it. You should now see a new thumbnail to the right of the layer set’s folder icon, and everything in your image should have disappeared except the bikini top.

You can see that the thumbnail for the mask is a grayscale image. What’s happening is that the black parts of the mask are hiding the pixels underneath them, turning them transparent. As I said earlier, masks behave very similarly to alpha channels. Realize though that this is faux transparency. It won’t be preserved when outputting the image to TGA since masks are not channels. They are just layer effects. For real transparency, you need real channels.

The advantage of using masks in this way is that they serve to give you a preview of what your transparency will look like. For images more complex than this simple bikini top, this can be very useful. However, once again, nothing that happens on a mask is “real”. To preserve the effect of the mask for output, the mask must be copied to an alpha channel.


6. You should still see the marching ants selection marquee around your bikini since we haven’t deselected anything yet, but if not, simply ctrl-click on the mask thumbnail to re-select. On the Layers Palette, click the tab that says Channels to switch it to the Channels Palette. What you should see listed here are the three primary channels for your image, labeled, "Red", "Green", & "Blue", and a master channel for the three, labeled "RGB". If you see any other channels besides those four, delete them now.


7. At the bottom of the Palette Window, locate the button that looks like a rectangle with a circle in the middle. It's the second one from the left. It says "Save Selection as Channel" when you hover your mouse over it. Click it.


8. You should now see a new channel called "Alpha 1", which is white inside the selection marquee, and black all around it. By default, this channel will have its visibility turned off. This is fine. The image will behave exactly the same in the end whether it’s on or off. It’s best at this point just to keep it off.


9. Click "Select" on the menu bar at the top of the screen to pull down the Select Menu. Click "Deselect" and you should see the marching ants disappear.


10. OPTIONAL STEP: "DEHALOING" - On the Layers Palette, create a new layer by pressing the button at the bottom right that looks like a square sticker being peeled from its backing. Click on the name of the layer set, and drag it above the new layer, so that the new layer is beneath it, but not inside it. Paint the new layer 50% gray or darker; black is fine. (The gray/black layer will prevent the white halo sometimes caused when Alphas are created the way we just did it. If you don't know what I mean by that, don't worry about. Just make sure to always put a gray/black layer underneath your work and you'll never have to see that white halo. Alternatively, more advanced users may wish to use one of the better halo-elimination methods discussed in the FAQ.)


11. Save your file as a 32-bit TGA and upload it to SL.




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Adobe Photoshop – Method 4: The Two-Second Method


This is the simplest and fasted method there is for creating an alpha channel. It consists only of two essential steps, in addition to saving the file. It won't accomodate for translucency or de-haloing without adding a few steps, but if all you're going for is full opacity against full transparency then these steps are all you need.


1. Select the area you want to be opaque using any of the marquee tools, or if the area in question is on its own layer, seperate from the background, simply ctrl-click the layer thumbnail to select the whole layer.


2. On the Select menu at the top of the screen, go Select -> Save Selection. On the dialog that pops up, make sure "New Channel" is selected (it will be by default), and click OK. If you now examine the Channels Palette, you'll see that a new channel was created, called "Alpha 1", with your selection area painted white, and the unselected area painted black.


3. Save your file as 32-bit TGA and upload it to SL.




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Adobe Photoshop – Robin Sojourner's Tutorial Video


For those whe prefer to learn by watching rather than reading. Click here for Robin Sojourner's excellent tutorial video. You'll also find other useful goodies on her site, such as advanced avatar templates, tools to help with texturing odd shaped prims, and much more.


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Photoshop Elements


This tutorial was made possible in large part by Robin Sojourner, who I believe was the first on this board to discover that PSE can create alpha channels, even though it does not display them. This has been tested with PSE retail versions 3 & 4.

UPDATE: Special thanks to ArchTX Edo for supplying a necessary addition in Step 3 of the tutorial in order to make it work for PSE version 2.0.

It is unknown at this time if this tutorial will work with version 1.x or with bundled or pre-installed versions.


1. On the Layers Palette turn off all layers except for the layer that has your bikini on it. (To turn a layer off, click the eyeball symbol to the left of its name.)


2. If the bikini layer has any white space around the bikini itself, use the eraser to get rid of the white space. It's very important at this stage that the bikini be on its own layer with nothing else on it. (NOTE: There are much better tools available than the eraser for this purpose. For the sake of simplicity in the tutorial, the eraser just happens to be the quickest one to talk about.)


3. On the Layers Palette, ctrl-click the thumbnail for the layer with the bikini on it. The thumbnail is the little picture of the layer directly to the left of the layer's name.

If using PSE 2.0, choose "select layer transparency" from the pop-up menu that appears. If you're using a newer version, you won't see that menu, so don't worry about it.

This will select everything on the layer. You should see the "marching ants" outlining your bikini now. If there are elements of the bikini on any other layers, hold down shift, and then ctrl-click their respective thumbnails to add them to the selection. Make sure not to include the background or any of the template layers.


4. On the Select Menu at the top of the screen, go Select -> Save Selection. This will save the selection a newly created alpha channel. Unlike Photoshop, PSE has no channels palette so you can’t actually see the alpha channel, but it is there.


5. If you still see the "marching ants" outlining the bikini shape, turn off the selection by clicking Select -> Deselect. For the next step, you'll want nothing selected.


6. OPTIONAL STEP: "DEHALOING" - On the Layers Palette, create a new layer by pressing the button at the bottom right that looks like a square sticker being peeled from its backing. Click on the name of this new layer and drag it underneath the layer with the bikini on it. Paint the new layer 50% gray or darker; black is fine. (The gray/black layer will prevent the white halo sometimes caused when Alphas are created the way we just did it. If you don't know what I mean by that, don't worry about. Just make sure to always put a gray/black layer underneath your work and you'll never have to see that white halo. Alternatively, more advanced users may wish to use one of the better halo-elimination methods discussed in the FAQ, although they may not all be applicable to PSE.)


7. Save as 32-bit TGA and upload to SL.




_________________________________________________
Paint Shop Pro


I should preface this by saying that I’m a Photoshop user so my PSP tutorials are not as detailed as my Photoshop ones. This will still walk you through what you need to do, but not with quite as much hand-holding as the Photoshop info.



1. Unlike Photoshop, PSP does not allow you to edit channels directly. So, you need to use a tool called a mask as a proxy for what will in the end become the alpha channel. To create a new mask, go Layers -> New Mask Layer -> Show All. A new layer group will be created, at the top of which will be your new mask layer. Make sure all other layers are in the group and below the mask.


2. On the Layers Palette, select the mask layer and make sure the little Mask Overlay Toggle button at the top is turned off. The Mask Overlay Toggle is directly to the right of the Link Toggle. It looks like a tiny picture of a theater mask. When it's off it's gray; when it's on it's red. Just so you know, turning it on can be useful so you can exactly what is happening with the mask itself, but you'll have a more WYSIWYG feel with it turned off.


3. At this point, your mask will be all white (no transparency yet). On the mask layer, start painting the areas you want to be invisible black, and you'll see the checkerboard show through in those areas. Any areas you want semi-transparent, paint gray. The darker the gray, the more transparent; the lighter the gray, the more opaque. The areas you want completely opaque just leave white.


4. When you're finished, go to Layers -> Load/Save Mask -> Save Mask To Alpha Channel, and then delete the mask (DELETE it, do not merge it) by right clicking on it in the Layers Palette and selecting Delete. If you need to edit the alpha later, go Layers -> Load/Save Mask -> Load Mask From Alpha Channel.


5. OPTIONAL STEP: "DEHALOING" - Create a new layer, and drag the layer set above it, so that the new layer is beneath the set, but not inside it. Paint the new layer 50% gray or darker; black is fine. (The gray/black layer will prevent the white halo sometimes caused when Alphas are created the way we just did it. If you don't know what I mean by that, don't worry about. Just make sure to always put a gray/black layer underneath your work and you'll never have to see that white halo. Alternatively, more advanced users may wish to use one of the better halo-elimination methods discussed in the FAQ, although not all of them will be applicable to PSP.)


6. Save your file as a TGA and you should be all set. Unlike Photoshop, PSP offers no option to choose 32-bit at the time of save. If an alpha channel is present in the image, the file automatically will be saved as 32 bit. If there's no alpha channel, the file will save as 24 bit.

Just to be thorough (thanks Jolan Nolan for pointing this out), there is an options button on the save dialog, which does include a bit depth selector, but I recommend leaving it alone. The dialog it calls up is kind of confusing. It allows you to select bit depth of 8, 16, or 24, but not 32. For SL purposes, leave it at 24 at all times (SL can't use 8 or 16). For some reason, the makers of PSP seem to think the extra 8 bits in the alpha channel aren't worth counting out loud, which is really strange, but don't worry; the file will still save correctly with 24 selected. As long as you work in RGB mode at all times, your images will automatically save correctly unless you tell it otherwise. To avoid problems, I recommend never pressing that options button unless you're sure you know what you're doing.




_________________________________________________
The GIMP


Tutorial coming soon.
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Robin Sojourner
Registered User
Join date: 16 Sep 2004
Posts: 1,080
01-04-2006 20:09
Thanks Chosen!

I just want to add a couple of things.

First, if you are using PS CS2 you won't see a little link where Chosen says to look for one in the third PS tutorial. You can link layers, but you can also just shift-select a bunch of them at once, so the link icon has been moved to the bottom left corner of the Palette. (Chosen doesn't have CS2 yet, so he wouldn't know this. :) )

Also, Sets are now called Groups. So, if you want to put all your layers in a folder, and mask the folder, as Chosen outlines in that tutorial, you'd do it by shift-selecting all the layers (or Command/ctrl selecting if there were other layers between the ones you want,) and choosing "New Group from Layers" from the menu.

Chosen's tutorials are wonderful teaching tools, and will really help you to understand what you are doing, so I highly recommend them to beginners.

But once you know what's going on, I would suggest a few changes.

First, don't use the eraser to eliminate any white on the bikini top. If you do, and accidentally erase some pixels you wanted, you can't retreive them once you have gone too many steps beyond the mistake or closed the file. (If you haven't gone too many steps, you can use the History Brush to paint them back in.)

Use a Mask, instead. Here's how.

1. If your layer is partially transparent already, Command/ctrl click on the thumbnail to select the non-transparent pixels, and then click on the Make Mask icon at the bottom of the layer palette. (It's the one that looks like a gray square with a white circle in it.) A layer mask will automatically be made. It will have black where there is transparency, white where there isn't, and gray in the areas that are partially transparent. (Sound familiar? :D ) If it's not, just click the icon to make a new blank mask.

2. Paint with gray or black on the mask to eliminate any unwanted pixels on the layer. You can tell if you're painting on the mask in CS2 by looking for the outline around the Mask thumbnail (the black and white one, to the right of the Layer thumbnail.) In earlier versions of PS, look for the mask icon, not the brush icon, in the column on the left of the Layer Palette. If you go too far, and accidentally eliminate pixels you wanted, paint with white or gray to retreive them.

3. If, at any point in this process, you want to see your mask by itself, hold down the Option/alt key and click on the Mask Thumbnail (the black and white image, to the right of the colored one, in the Layers Palette.) The picture will vanish, and you'll just see the mask, in all its grayscale glory. :)

4. If, at any point in this process, you want to turn the mask off, so you see the image without it, hold down the Shift key and click on the Mask Thumbnail. To show it again, just click on the Mask Thumbnail again.

5. When you are happy with it, Command/ctrl click on the Mask Thumbnail (not the Layer Thumbnail,) and Save Selection. That mask will become your new Alpha channel.


Also, once you throughly understand what is going on with Alpha channels, don't be afraid to experiment with ways to streamline the process in your own workflow. As the slogan says, "Work smarter, not harder."
_____________________
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www.robinwood.com

"Second Life ... is an Internet-based virtual world ... and a libertarian anarchy..." Wikipedia
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
01-04-2006 20:31
Thanks for the additions, Robin. That's exactly the kind of supplimental info I was hoping people would add.

Just so you know, I agree with you about the mask vs. the eraser. Masks are much better, and I'm always in favor of non-destructive vs. destructive workflow. It's just that from a new user perspective, I believe the eraser is more intuitive and easier to teach. It's all baby steps.

My ultimate hope is that in-depth beginner tutorials like this will get stickied so that new people can have their questions answered automatically, and people like you and me will then have more time to discuss more advanced techniques. I enjoy teaching beginner level for sure, but after answering the same questions 10,000 times and not a whole lot inbetween, I could do with a little more flavor in my diet.
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Cottonteil Muromachi
Abominable
Join date: 2 Mar 2005
Posts: 1,071
01-05-2006 03:34
Maybe you could include screenshots with annotations and output it as a .pdf. It would help newbies a lot more.
Nepenthes Ixchel
Broadly Offended.
Join date: 6 Dec 2005
Posts: 696
01-05-2006 05:41
From: someone


I’ve heard Photoshop 7.0 is bugged, and that it handles transparency differently than all other versions of Photoshop. Is this true?

Yes, it’s true. Anyone using 7.0 should download the free 7.0.1 update from Adobe before proceeding any further.


I like my 7.0. Make appropriate bits transparent using layer masks (not erasing) and grouped layers, save as a 32bit TGA... easy and simple. No white halos, no need for special dark grey layers, no need for an explicit alpha channel.

So what am I missing? If it's just the ability to select an arbitary alpha channel to same as the image's alpha channel it's not something I need given the way I use layers.
Robin Sojourner
Registered User
Join date: 16 Sep 2004
Posts: 1,080
01-10-2006 14:53
As I said in a different thread (but will quote here, since this one is a Sticky! Woot!)

From: Robin Sojourner
There are a number of problems with it, which is why Adobe abandoned that particular way of handling .tga files very quickly.

The Big Three, which come immediately to mind;

1. When you use that plug-in, your alpha channel is pre-multiplied, which makes it invisible and un-editable. If you decide that you want to change something about the image transparency later, you can't do it, unless you saved a backup Photoshop file. (Something which I always recommend you do anyway; but sometimes things happen to saved files. This plug-in eliminates one safety net.)

2. Pre-multiplied alpha fades to black, not white, so you are getting black halos, not white ones. They aren't as noticeable in ordinary circumstances; but that doesn't mean that they aren't there. If you use an alpha channel, you can totally eliminate any halos.

3. Not all programs can correctly read files with pre-multiplied alphas. In those cases, the areas that you expect to be transparent will show as black, and it might be extremely difficult to extract your image from that black background. There was a whole thread about this recently in a different graphics forum, but I can't find it at the moment.


Given all of this, and the fact that you can make a real alpha channel in three or four mouse clicks, without ever opening the Channel palette, it makes sense to make real alphas.

I've said it dozens of times, and will probably say it dozens more. You don't need to edit alpha channels to have them. All you have to do is be able to hold down a key or two with one hand, and click with the other. :D

1. From any multi-layered image at all, no matter how it's constructed, if you hold down Shift+Alt+Ctrl (Shift+Option+Command on a Mac) and tap the E key, you'll make a composite layer, with your whole image on it, including all the various kinds of transparency etc. (NOTE: if you are using a version of PS prior to CS2, make a new layer first, and select it before you use these keys, so the composite will be made in that layer. CS 2 makes a new layer automatically.)

2. Hold down Ctrl/Command, and click the thumbnail image for that composite layer. That selects the opaque pixels, according to their opacity. (Totally opaque are totally selected, 50% opaque are 50% selected, 0% opaque are not selected at all.)

3. Go to the Select menu, and Save Selection. Your alpha channel is made. You don't need to look at it, edit it, or interact with it in any way.

4. (Optional, but highly recommended.) If you want to totally eliminate any halos, just run the free Solidify filter from Flaming Pear on that composite layer after you've made the Alpha. Single mouse click, no chance of halos, no touching of the Alpha channel.


If you don't have layers in your image, it's even easier. If you have a mask, just do steps 2 and 3 above, but click on the Mask thumbnail, not the Image thumbnail, in step 2. Hold down the shift key and click the Mask to disable it, after you've made the alpha but before you save the .tga, and you'll not only have no chance of halos, but a backup of your image, saved in targa format on the SL servers.

If you don't have a mask or layers, then just do steps 2 and 3, and then run Solidify.

The thing is, there are problems with the old 7.0 plug-in, and making an alpha is extremely easy and requires no editing of alpha channels at all!

I'm not telling you that you have to switch methods, Lo. You're a grown-up. Do whatever you think is best for you. :D

I'm just interested in people making an informed choice. Here's the information. Everyone can now choose to do whatever they like with it.


So there you go.

Also, Chosen didn't mention them, but if you learn better from video tutorials, I have a couple dealing with transparency here. Just click on "Alpha Map Transparency" and "Lace Textures" on the left side of the page.
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www.robinwood.com

"Second Life ... is an Internet-based virtual world ... and a libertarian anarchy..." Wikipedia
Blueman Steele
Registered User
Join date: 28 Dec 2004
Posts: 1,038
required reading
01-10-2006 15:18
ok from now on this is required reading for anyone attending my photoshop classes.
Chip Midnight
ate my baby!
Join date: 1 May 2003
Posts: 10,231
01-10-2006 15:26
OMG a sticky! It's about time. Here are some other very useful threads...

CMFF custom clothing and skin templates. Far more detailed and easier to use than the Linden supplied templates, with edge and seam matching guides.

Robin Sojourner's custom clothing and skin templates. Another set of alternate templates that beat the pants off the Linden templates with some great features for people who prefer to work with vectors.

Robin Sojourner's T-Shirt Template. Includes a great base t-shirt texture and instructions on how to add your own design to it.

Whisper Lily's sample alpha channel for bikini bottoms. This is one of the hardest clothing items to figure out how to do well. Now you don't have to.

Namssor Daguerre's Free Makeup Kit for Photoshop. Contains a ton of useful features to help you create makeup tattoos in Photoshop as easily as you can create makeup in SL's appearance mode.

Nephilaine Protagonist's basic tutorial for making a shirt
in Photoshop. Step by step instructions to help you get started making a clothing item.

Cindy Claveau posted some nice Photoshop tutorials on using the Burn and Dodge tools.

Nicola Escher's great clothing tutorials in PSD format.

There are certainly more must read threads but these are ones I could think of off the top of my head. Please add others.

If you have questions about any of the links in this post please ask them in the linked threads and not in this sticky.
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Jennifer McLuhan
Smiles and Hugs are Free
Join date: 22 Aug 2005
Posts: 441
Required Reading
01-10-2006 16:00
Way to go Chosen! Here I think I have all the material together for my class, all the handouts and textures...and you go and publish this.

*** best hands on hips glaring posture ***

LOL - Beautiful - I will just add the URL to the hand out folder.

Linden Labs should pay you and a few others for all the help you give.

Philip, Jeska, if you read this, LL needs to have a Supreme Service Award for people like Chosen who help keep paying customers, like me, happy; so, we will continue to line your pockets with gold.

:-)

Jen – Who is in a bubbly mood.
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
01-10-2006 17:23
Thanks for all the feedback so far, everyone. Robin, I've updated the tutorial post with a section for your videos. Your alpha video channel video was already linked in the FAQ section, but not very prominantly like it should have been. The new addition is under the Photoshop tutorial heading, and contains two links. One goes straight to the alpha channel video, and the other goes to your page with all your tutorials and templates and stuff.

Sorry I didn't do a better job of including your stuff earlier. I wrote the entire guide in one six-hour marathon, and my brain was pouring out my ears by the end of it. I'm sure there will be plenty more to add as time goes on.
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Oshee Udal
Registered User
Join date: 30 Dec 2005
Posts: 1
wow
01-29-2006 01:37
Not only is she smart,she's wicked hott as Seven of nine...

^^
with love


Oshee Udal
Nicola Escher
512 by 512
Join date: 1 May 2003
Posts: 200
01-29-2006 12:35
My prayers have been answered. A stickied guide to alpha channels. I may die peacefully now. Way to go!

Many many kudos,
Nicola
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NicolaEscher.com
Tutorials, fashion, and photos.
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
02-09-2006 10:39
I've added to the Photoshop tutorial section to include a fourth method, which I call "The 2-Second Method". The tutorial contains its own description so I'll refrain from commenting further here. I've added this post here just so that people will realize there's something new in the thread. If anyone has any questions, let me know.
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Robus Talamasca
Registered User
Join date: 17 Sep 2005
Posts: 8
Alpha in Photoshop Elements ver 4
02-13-2006 16:59
I tried using Robin and Chosen's alpha techniques in Photoshop Elements 4, since I was traveling and didn't have full Photoshop on my laptop.

I never could get it to work. I could create the alpha channel, but when I saved the .tga, it didn't have the alpha. Is this a "feature" Adobe removed for version 4? Or was I just doing something wrong? Now I'm back to my full PS CS2 setup, it doesn't matter but I've been curious ...

--RT

Edit: The problem turns out to be in the graphics driver of my notebook, not PS Elements 4. Sorry to lead folks astray.
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
02-13-2006 17:05
From: Robus Talamasca
I tried using Robin and Chosen's alpha techniques in Photoshop Elements 4, since I was traveling and didn't have full Photoshop on my laptop.

I never could get it to work. I could create the alpha channel, but when I saved the .tga, it didn't have the alpha. Is this a "feature" Adobe removed for version 4? Or was I just doing something wrong? Now I'm back to my full PS CS2 setup, it doesn't matter but I've been curious ...

--RT

Interesting question, Robus. I haven't used version 4. I will definitely look into this. Thanks for the heads up.
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Punkerella Summers
Registered User
Join date: 14 Feb 2006
Posts: 1
A temp solution for Gimp Users
02-20-2006 23:30
Hi there, I found you info super helpful. I am a gimp user but the explanation was plenty to get me started. I found this http://glscene.schtuff.com/tips_alphachannel has a short explanation of adding an alpha channel with gimp. You might want to point gimp users that way until you have finished that section. Thanks for your wonderful tutorial :)

-Heather
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
02-21-2006 22:07
Thanks for the addition, Punkarella. I haven't yet had time to play around with GIMP much since posting this guide. I'm currently out of town, but when I get home I'll try the tutorial in your link just to verify the steps are right. I'm sure it's all good, but I won't post anything I haven't tried. Assuming it works, I'll have the GIMP section of the tutorial post updated soon after.

Thanks again.
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Jolan Nolan
wannabe
Join date: 12 Feb 2006
Posts: 243
03-02-2006 16:34
I'd like to point out a (possible) mistake under the Paint Shop Pro instructions, Step 6. It says that there is no way to change the bit depth when saving TGA with transparency. When going Save As, under Cancel there's an Options button with 3 options: 8, 16 and 24. 8 will flatten everything and 16 and 24 will save 1 alpha each.

- Jolan
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
03-02-2006 21:30
From: Jolan Nolan
I'd like to point out a (possible) mistake under the Paint Shop Pro instructions, Step 6. It says that there is no way to change the bit depth when saving TGA with transparency. When going Save As, under Cancel there's an Options button with 3 options: 8, 16 and 24. 8 will flatten everything and 16 and 24 will save 1 alpha each.

- Jolan

Thanks, Jolan. If there's a mistake, I'll correct it. Can you elaborate on this? I'm out of town at the moment, so I don't have PSP in front of me to look at what you might be talking about. As I said earlier, my PSP knowledge is very limited compared to my Photoshop knowledge.


EDIT: I finally had a little time to take a look at what Jolan was talking about here. It seems we were both right. There is an option to change bit depth when saving TGA in PSP, but its definition of bit depth seems to be a little weird. There is no option for 32. It's as if they think the extra 8 bits in the alpha channel don't count or something. That makes options pretty much useless, at least from an SL standpoint. I've edited the tutorial to describe the options menu and how to use it for SL-purposed images (which basically means leave it alone). Thanks again for pointing it out, Jolan.

Just so everyone is aware, SL will not import 8-bit (B&W) or 16-bit (grayscale) TGA's. It will only accept 24-bit (RGB) or 32-bit (RGBA) images. Therefore, for SL you have to keep the option set on 24 at all times, which is the default option anyway if you were working in RGB mode all along, which you always should be for anything you make for SL. From there, just like it said in the tutorial originally, PSP will create a 32-bit TGA if there's an alpha channel present, and a 24-bit one if there isn't.

It's very odd that they give you 8, 16, and 24 as choices, but not 32. I can see no logic setting it up that way. Really weird.
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Lily Pussycat
Registered User
Join date: 21 Aug 2005
Posts: 28
Thank You!!!
03-06-2006 20:18
WONDERFUL tutorial ... and I have been pulling my hair out trying before I found this.
Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
03-11-2006 11:27
From: Robus Talamasca
I tried using Robin and Chosen's alpha techniques in Photoshop Elements 4, since I was traveling and didn't have full Photoshop on my laptop.

I never could get it to work. I could create the alpha channel, but when I saved the .tga, it didn't have the alpha. Is this a "feature" Adobe removed for version 4? Or was I just doing something wrong? Now I'm back to my full PS CS2 setup, it doesn't matter but I've been curious ...

--RT

Robus, I finally had time to test this in PSE 4, and it works just fine. There are a couple of easy ways to screw it up though. First, if you save your TGA as 24-bit instead of 32-bit, it won't have any transparency. Second, if you've got more than one selection saved, your alpha channel will wind up being 100% white. Make sure when you save your selection the first time, you name it "Alpha 1" and from then on, if you have need to save the selection again, make sure to either add the new selection to Alpha 1, or else replace it. Don't have multiple selections saved, or you'll have problems.

If you're in doubt, just go Select -> Delete Selection... and then delete every item listed, one by one. Then when it's all clear, make your selection and save it as Alpha 1. Output as 32-bit TGA, and you're all set.
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Chosen Few
Alpha Channel Slave
Join date: 16 Jan 2004
Posts: 7,496
03-18-2006 08:55
I finally had time to research Jolan's comment about the TGA options menu in PSP. For details, scroll up a couple posts and read the edit addition to my original response.
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Jolan Nolan
wannabe
Join date: 12 Feb 2006
Posts: 243
03-18-2006 13:33
PSP is a little buggy for me - sometimes it saves the TGA and sometimes it flattens it with no Alpha. So here is a way using a program called "DXTbmp". It is a program for editing DXT files but can also save 24-bit TGA's with Alpha and is quite easy to use. Any picture program can be used but for this tutorial I will be using Paint Shop Pro.

DXTbmp homepage

PSP
1. First set your background color box pure green.
2. Using the Magic Wand, select all the areas that you want to be transparent and delete them, thus turning the areas to green.
3. Save the file as a .TGA

DXTbmp
1. Open the TGA image.
2. Under 'Alpha', select 'Create alpha channel (Green)' and it should create an alpha out of all the pure green areas.
3. Save

*Note*
In the event that, for whatever reason, the alpha channel looks all crewed up in the preview window on the right, simply make a 2-color B&W (with the black as the desired transparent spaces) and save it as a .BMP. Now in DXTbmp, select 'Alpha' and 'Import alpha'. Select the .bmp and then Save.

- Mike
Namssor Daguerre
Imitates life
Join date: 18 Feb 2004
Posts: 1,423
03-24-2006 02:12
bump
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