A sharpening guide was requested at my Ask The Maker thread. :)
Also, sorry if I'm rambling too much in this. I don't really know how to make a guide, so I'm just trying my best here. :P
My way of iconing (including sharpening) usually goes like this:
Crop the screencap to 200x200
Play around with the icon. Colors, lighting, textures, blending etc.
Sharpen using paint daubs
Re-size the icon to 100x100
Not happy with the icon, play more around with it
Needs more sharpening, use high pass on low opacity
Make some adjustments to the lighting
The different ways of sharpening (that I use)
Let's take a look at this icon:
It has not been sharpened in any way. It looks a bit blurry in her face.
Now, as I've said previously, I start making my icons at a 200x200 canvas, so this is what I would be looking at:
If you want to use paint daubs, which is my favorite way of sharpening, stamp your layers (ctrl+alt+shift+e), (or flatten, but you lose your layers if you do that) and go to Filter>>Artistic>>Paint daubs. Set both settings to 1 and brush type to simple. You can of course use higher values, but that looks too sharp in my opinion.
And always use this type of sharpening before re-sizing to 100x100. But if you want to use it when your icon is 100x100 you can lower the opacity of the layer and/or erase the parts where it's too sharp.
not sharpened || paint daubs
I would probably have erased the parts over her ears, upper lip, edge of her left cheek and the tip of her fingers, as I think they look too sharp.
My result after erasing:
I often use this one later in my process of making the icon if I think it needs more sharpening even after using paint daubs and playing around with the icon more.
Stamp your layers, go to Filter>>Other>>High pass. I set the radius to 1,5 pixels. Set this layer to soft light:
unsharpened || high pass
I would also here erase the parts I mentioned above.
You can also set the high pass layer to overlay or hard light for a stronger effect.
I rarely use this way, I used it much before though. If I do use it, it's usually on really low opacities (2-15%) to get that final sharpness needed.
Just go to Filter>>Sharpen>>Sharpen:
unsharpened || sharpen
I find this too sharp, so I'm gonna lower the opacity to 55% and erase the parts that are too sharp (same as before):
There are also other ways of sharpening, like unsharp mask, sharpen more etc.
But I'm afraid I don't know enough about them to say anything about them.
unsharpened || paint daubs || high pass || sharpen
As you can see, there aren't really any huge differences. Just use the way you like the best.
And of course, how sharp is too sharp is a matter of personal taste.
Sometimes I oversharpen an icon on purpose because I think it fits the cap, scene and/or style of the icon. Like these for example:
Also if you are using grainy textures and want to enchance their effect, you can sharpen a little extra.
Some general sharpening tips at the end:
• Never sharpen your base. Work with the lighting and coloring first. That way you can see how much sharpening is necessary and not end up with an oversharpened icon.
• The more contrast you have in your icon, the less sharpening you need.
• If you have added gradient maps with colors, your icon can often take more sharpening without looking too sharp
• Always use the highest quality screencaps/pictures available, this is the number one rule really.
• You don't have to sharpen all icons. Many icons can go just well without this (note what I said about contrast). :)
And as always, if you have a questions, just speak out!