getting rid of alpha halos in GIMP

Has anyone found or written a tutorial on eliminating halos in the GIMP? I am learning GIMP by trial and error, but so far none of my experiments in getting rid of halos has worked very well.

Thanks!
SJ

Doesn't anyone know how to do this? I am still experimenting, but no luck so far, probably due to my inexperience with GIMP.

I was never able to figure it out myself, which is why the sticky still doesn't have a GIMP tutorial in it. Granted, I haven't had a ton of time to play with GIMP, so it's very possible I missed something, but the only work flow I was ever able to make it do is WYSIWYG when it comes to transparency. I wasn't able to make it treat layer transparency and alpha transparency as two different things, which is what you need to do in order to control things like haloing.

Id love to help you, but in all my time with Gimp (absolute newbie in all graphics applications to today) I have never had a problem with halos unless I did something obvious like leave a ring of colored pixels on the image. I can only assume that you are bringing something to it from the Photoshop workflow that is causing this artifact.

Use the select tools and use feathering.
If its an external type halo, use the Fuzzy Select tool and click outside the image (where you want transparency). Use the threshold and feathering options to get the amount of edge you wish to remove then press Ctl K to clear the selection, press Ctl K again and maybe again to remove the halo gently.

Key is amount of threshold and feather.
Reduce feather for each Ctl K (clear selection) for a sharper edge.
You will end up with a nice smooth edge but it may take a couple of goes to get right.
Ctl Z is our friend.

Works for me and is quite simple, there is no need for a tutorial on this.
BTW Install the Gimp help files, which are separate, then you will have context sensitive help on most aspects of Gimp.

You can get fine control over the edges by adding a layer mask by transferring the alpha channel.

In The Gimp 2.4rc3 it goes like this:

(Menu) Layer - Mask - Add Layer Mask

Select "Transfer layer's alpha channel" and press "Add"

In the Layers dialog you should see the layer mask next to the layer. It is black for transparent and white for opaque. Any grey parts are semi transparent.

Right click on the layer and select "Show Layer Mask", "Edit Layer Mask" should be selected already, leave that as it is.

Use the "Select by color tool" to pick the black parts.

Make sure your background color is set to black, you can hit the little arrow to switch foreground and background colors if needed.

(Menu) Select - Grow

This will ask for a number of pixels. You need to enter just enough to remove the halo, 2 or 3 may be enough. Use more if you want faded edges rather than sharp.

Press "Delete" key. Your selection will go black.

Depending on effect you want at the edges you could remove the selection and do a blur to have smooth faded edges. You'll generally need to to grow the selection more if you are doing this.

You can check the edges by right clicking the layer again and disabling "Show Layer Mask".

If you are happy then right click the layer and "Apply Layer Mask"

Save your haloless image.

You can use all the normal tools on the layer mask, so if only a few parts need cleaning, you may be better with a black pencil and painting the mask. You can do this with "Edit Layer Mask" checked and "Show Layer Mask" unchecked, so you can see the halo and just paint it out.

Many thanks! This is very helpful. Up until recently I was exclusively a Photoshop user, so it has been tough for me to switch gears.

Thanks again!
SJ

i just save as png with no options checked

you cant have a halo if theres no bg color data

This is totally cheating and Chosen Few would shred my knuckles with a cheese grater for saying this, but this is how I do it.

When you create a new file, under the Advanced options, fill with transparency. The Alpha channel continuously updates itself and you never have to touch it. I've never had a problem with halos no matter how slapdash I work.