Textures altering in SL

Can the way an texture renders change after it has been uploaded to SL? On two occasions now I've uploaded images that were quite noisy. After adding them as textures immediately after uploading I wasn't happy. They appeared very bitty and shimmered from a distance, in an ugly way. I'd compare it to a tv picture without a reception. But then, after exiting SL and returning later, I tried the textures again and they seemed softened somehow and in keeping with the SL environment. Is this possible? What's happening? I uploaded them as 512x512 TGA files and on separate occasions.

Albion

Hiya Albion,

I'm not sure they can change once in secondlife, However I've noticed if I save them at 32 tga they are higher quality once in secondlife then saving as say 24 tga.

Could it have been that hey didn't rezz completely when you first uploaded them? that could explain them looking better when you logged back in

Nat

This is not possible. It is very common among those new to texturing to assume that more bits must somehow be better than less bits, but it just isn't so. I explain this in detail in the transparency guide at the top of this forum, which I highly recommend you read, but I'll summarize quickly here as well.

Images for the screen are comprised of components known as channels, which govern various characteristics. Color TGA images have 3 channels, red, green, and blue. Color TGA's with transparency also have a fourth channel called Alpha. Each channel contains 8 bits of data (per pixel).

Color images are 24-bit by easy math. 3 channels times 8 bits = 24 bits. If the image has transparency, that fourth channel adds another 8 bits, bringing the total to 32.

Never ever save an image as 32-bit unless it actually needs transparency in it. Otherwise you end up with problems. First, your files will be 33% larger than they should be, and second, you'll add to the ever-present alpha sorting glitch common to almost all OpenGL applications, SL included. The glitch causes 32-bit images placed in close proximity to eachtother to appear to switch positions or cancel eachother out.

In any case, it's absolutely impossible for the extra 8 bits to improve the quality of the image in any way. That's simply not how it works. The fourth channel just adds transparency data. That's it. If you believe you're seeing something more, then no offense, but I'd suggest it's nothing more than your brain playing tricks on you, a manifestation of wishful thinking from your assumption that those extra bits must somehow be enhancing the image. Again though, that's just not how it works.

I'll repeat, NEVER save images as 32-bit unless you need them to be transparent.



Anyway, Albion, I would agree with the second part of Natalie's post. Chances are the textures just didn't fully rez for you the first time around. There's no way they could have changed after they were uploaded. When you upload an image, SL compresses it into JPEG2000 format. That compression is a little bit lossy (it's optionally lossless, but SL doesn't use the lossless setting), which means if your pre-existing "noise" were fine enough, it could end up disappearing upon conversion. Of course, the opposite effect could also happen, and the noise could get enhanced, making your image look much worse. The exact outcome will vary from image to image, depending on the mathmatics of how the image is composed.

Once they've been uploaded to SL though, all images are just asset files like anything else. They just get referenced from the asset server, and sent to the various locations inworld where they're supposed to appear when you view them. They can't change.

Hey I know exactly what you are speaking about here. I have a particular textures I use as a border on my sales boxes. Upon first upload the border shimmers and carries on (The border has gold in it) and I always look at it and go hrm and compare it previous boxes I have made which are not doing this, no tiwnkiling etc, they are however fully rezzed. I can go away come back to the same place and still it is there, log off then back on again and the boxes appear to be the same as the others. I have no clue what causes this, but I can live with it

Hi!

I've noticed this behavior as well. The "shimmering," by the way, is commonly known as "Pixel Crawl." It happens when a texture has small areas of very different values which causes the rendering software to show the lighter value on one screen pixel on one screen refresh, and an adjacent pixel (or not at all, depending on the size of the area) for the next one. Since the screen refreshes every few seconds, the result is the shimmering you see.

I'm not sure why it "goes away" when you log out and back in. But yeah, it does do this. You're not going crazy, or seeing things, or anything like that.

But I don't think it's the texture itself changing in any way. It's the way in which SL displays it that changes.

And that changes for more things than pixel crawl. If you've noticed, textures on cylinders aren't displayed the same way now that they were before Flexi-prims. They've changed the way the texture is mapped, and didn't bother to tell us. Sigh.

Thanks for the replies. Glad to hear that I didn't imagine it. I wonder if it might be something to do with the compression that takes place and that it didn't load properly when I tried applying it immediately after uploading.

Hi Robin, I have your texture tutorial place landmarked. It's very useful. I've enjoyed walking through your land too. I'll remember to call it 'pixel crawl' in future. It sounds more appropriately unpleasant than 'shimmering'.

Albion

Thanks, Albion! I'm glad that you enjoy my work.

The other advantage of knowing that it's called "Pixel Crawl" is that you can Google it, if you want to read a bunch of discussions of the phenomenon.

(It's also called "temporal aliasing", by the way. But since that term applies to non-CG Art stuff as well, like the "wagon wheel effect" where (in film, strobe light, or while humming or eating crunchy food,) spoked wheels appear to move backwards although they are actually moving forwards, most people I know just use "Pixel Crawl."

But if you're in a surfin' kind of mood, there's interesting stuff under all these headings.

Robin Sojourner has osme of the best in game tutorials you can find also remember this. Not only is the work superb, but the teachings are most valuable, a must for anyone trying to texture and build in SL. Another one to pay close attention to is Chip Midnight. Look them up in SL and visit thier places. There are always things to learn even if you think you know what your doing already.

Ha ha I like that. It sounds like some kind of star trek transporter issue.