how to go from:
to 
Program: Photoshop CS4
Translatable: not really; uses selective coloring
Other: works best with dark, low-contrast, green/yellow images
Step 1. So I started with this picture of Adora Belle Dearheart from Terry Pratchett's Going Postal. It aired very recently, so the screencaps aren't on par with what I usually work with. This one was taken by me.
Step 2. I cropped it down to size, and sharpened it.
Unsharp Mask
Amount: 25%
Radius: 1.0 pixel
Step 3. Next up I added a Levels Adjustment layer. Normally I'd play with this until I get the colors looking exactly the way I want them, but that's not really an option with this kind of a base. So I push things up as much as I can until I start losing quality. I make the darks darker, the lights lighter, and bring up the middle as much as possible to try and lighten up the whole thing.
Levels (RGB): 20, 1.40, 195
Step 4. Keep in mind that in the first couple steps, I'm not actually caring about color. I just want to get the contrast and shading somewhat decent without sprinkling artifacts all over the thing.
That said, it's time to add a Brightness and Contrast Layer. The whole icon is still very muted and there isn't really any "white" whiteness to the thing so it's time to crank up the brightness.
Yes, the yellow might be scary but, like I said, overall look first, color later. Oh and we're increasing the contrast too, for what I hope are obvious reasons. Not too much though, otherwise we'll start ruining the base again.
Brightness: +71; Contrast: +30
Step 5. Now we'll start to work on the color; let's add a Hue and Saturation Layer, shall we? That yellow is atrocious, so it's going to be the first thing to go. I've never minded a bit of red, so I nudged the hue back towards the red end of the spectrum but only by a little; otherwise it will look like Adora's face got hit by a tomato. Mostly I pulled the saturation down since there will be other colors to take its place. Increased the brightness so her face is white instead of grey.
To make up for the loss of yellow, I increased the master saturation a bit. Not too much though. Then again, when dealing with master saturation and hue shifts it's always "not too much" with me.
Hue and Saturation
Master: Saturation +5
Yellow: Hue -5; Saturation -40; Lightness +15
Step 6. The icon is getting better, but all of the colors are still very faded. So, time for my favorite part, Selective Coloring. Add a Selective Color layer. I love red, so I'm going to increase and darken that. Same thing goes for any bit of yellow that's still there; add some red to it and darken (though not as dark as the actual reds). If any parts of the face/icon are looking a bit too white now, feel free to darken those as well.
As for the neutrals; like I said I love red. But red doesn't look as nice if it doesn't have a little yellow to soften it. And by darkening the neutrals just a little, I find you get a bit more contrast without screwing up the image and adding artifacts like the actual contrast command does.
Same thing with the blacks, except instead of adding red and yellow, we're going to be adding cyan and blue. Cyan doesn't equate in that muchbecause it's a subtractive color, so just make sure that the black meter equals or is greater than the blue you put in (especially on the images where the black is already rather greyish) otherwise you're going to have have... well, it's not going to be black.
Selective Coloring
Reds: -15, 0, 0, +30
Yellows: -25, 0, 0, +15
Whites: 0, 0, 0, +15
Neutrals: -20, 0, +5, +4
Blacks: +20, 0, -14, +25
Step 7. Looking a lot better, but a little more contrast between the different colors would be very nice. Last adjustment layer is Color Balance. Starting with the shadows, it's time to get the spots that Selective Color didn't. That will pop out the blacks and help them look cyan/blue without washing the vibrancy out.
As for the midtones, the cyan/blue of the shadows we just did sometimes washes out the neutrals from selective coloring, so I tend to add some more red back in to even things out. Not yellow though. I am done with yellow. To brighten up the face I put a bit of cyan in the highlights; not too much though or the actual color cyan starts to show. (I've never been a fan of cyan skin. Sorry.)
Color Balance
Shadows: -24, 0, +10
Midtones: +20, +2, +5
Highlights: -5, 0, 0
Step 8. Last (and I always do this last) but not least... well, maybe least. Anyways, when I get to the end and a character's face is still a bit yellow, I go to Image > Adjustments > Replace Color. I eyedropper the face, bring the hue back about 5 and increase the brightness by 1 to 5.
It really depends on the base you're using and it's very minor, but I can see the difference. Mostly it's to replace the yellow with a more natural skin tone... or at least as "natural" as you get in icons. (This particular step works with cartoons as well.)
Replace Color
Fuzziness: 85
Replacement: -5, 0, 1
Use your blur brush to brush out some stray (if there are any) artifacts in the background, and you're done!
Other Examples
to Program: Photoshop CS4
Translatable: not really; uses selective coloring
Other: works best with dark, low-contrast, green/yellow images
Step 1. So I started with this picture of Adora Belle Dearheart from Terry Pratchett's Going Postal. It aired very recently, so the screencaps aren't on par with what I usually work with. This one was taken by me.
Step 2. I cropped it down to size, and sharpened it.
Unsharp Mask
Amount: 25%
Radius: 1.0 pixel
Step 3. Next up I added a Levels Adjustment layer. Normally I'd play with this until I get the colors looking exactly the way I want them, but that's not really an option with this kind of a base. So I push things up as much as I can until I start losing quality. I make the darks darker, the lights lighter, and bring up the middle as much as possible to try and lighten up the whole thing.
Levels (RGB): 20, 1.40, 195
Step 4. Keep in mind that in the first couple steps, I'm not actually caring about color. I just want to get the contrast and shading somewhat decent without sprinkling artifacts all over the thing.
That said, it's time to add a Brightness and Contrast Layer. The whole icon is still very muted and there isn't really any "white" whiteness to the thing so it's time to crank up the brightness.
Yes, the yellow might be scary but, like I said, overall look first, color later. Oh and we're increasing the contrast too, for what I hope are obvious reasons. Not too much though, otherwise we'll start ruining the base again.
Brightness: +71; Contrast: +30
Step 5. Now we'll start to work on the color; let's add a Hue and Saturation Layer, shall we? That yellow is atrocious, so it's going to be the first thing to go. I've never minded a bit of red, so I nudged the hue back towards the red end of the spectrum but only by a little; otherwise it will look like Adora's face got hit by a tomato. Mostly I pulled the saturation down since there will be other colors to take its place. Increased the brightness so her face is white instead of grey.
To make up for the loss of yellow, I increased the master saturation a bit. Not too much though. Then again, when dealing with master saturation and hue shifts it's always "not too much" with me.
Hue and Saturation
Master: Saturation +5
Yellow: Hue -5; Saturation -40; Lightness +15
Step 6. The icon is getting better, but all of the colors are still very faded. So, time for my favorite part, Selective Coloring. Add a Selective Color layer. I love red, so I'm going to increase and darken that. Same thing goes for any bit of yellow that's still there; add some red to it and darken (though not as dark as the actual reds). If any parts of the face/icon are looking a bit too white now, feel free to darken those as well.
As for the neutrals; like I said I love red. But red doesn't look as nice if it doesn't have a little yellow to soften it. And by darkening the neutrals just a little, I find you get a bit more contrast without screwing up the image and adding artifacts like the actual contrast command does.
Same thing with the blacks, except instead of adding red and yellow, we're going to be adding cyan and blue. Cyan doesn't equate in that much
Selective Coloring
Reds: -15, 0, 0, +30
Yellows: -25, 0, 0, +15
Whites: 0, 0, 0, +15
Neutrals: -20, 0, +5, +4
Blacks: +20, 0, -14, +25
Step 7. Looking a lot better, but a little more contrast between the different colors would be very nice. Last adjustment layer is Color Balance. Starting with the shadows, it's time to get the spots that Selective Color didn't. That will pop out the blacks and help them look cyan/blue without washing the vibrancy out.
As for the midtones, the cyan/blue of the shadows we just did sometimes washes out the neutrals from selective coloring, so I tend to add some more red back in to even things out. Not yellow though. I am done with yellow. To brighten up the face I put a bit of cyan in the highlights; not too much though or the actual color cyan starts to show. (I've never been a fan of cyan skin. Sorry.)
Color Balance
Shadows: -24, 0, +10
Midtones: +20, +2, +5
Highlights: -5, 0, 0
Step 8. Last (and I always do this last) but not least... well, maybe least. Anyways, when I get to the end and a character's face is still a bit yellow, I go to Image > Adjustments > Replace Color. I eyedropper the face, bring the hue back about 5 and increase the brightness by 1 to 5.
It really depends on the base you're using and it's very minor, but I can see the difference. Mostly it's to replace the yellow with a more natural skin tone... or at least as "natural" as you get in icons. (This particular step works with cartoons as well.)
Replace Color
Fuzziness: 85
Replacement: -5, 0, 1
Use your blur brush to brush out some stray (if there are any) artifacts in the background, and you're done!
Other Examples