Hi there! So, I'm not much of a Painter user, but there are a few things in the program I'd really like to have access to in Photoshop. One of these is the glow brush, that fantastic little invention that artists like Ryan Church use to such great effect. It's not perfect for everything, and it's no substitute for actually knowing what you're doing, but it's pretty cool. Obviously, Corel and Adobe aren't going to be swapping their algorithms any time soon, so I decided to try to figure out how best to emulate the effect in Photoshop. Here are my results. Enjoy putting these techniques to use if you want!
The first thing to do is set up the brush itself. You'll want to use Photoshop's minimum-hardness round brush for the tip. Set size jitter and opacity jitter to pen pressure. Spacing is around 25% for me. You can also throw in some scattering if you want, but this tends to look bad at small brush sizes. Now set the flow to 1% - yes, 1% - and the brush blending mode to Screen. You may want it a little higher than that, depending on how quickly you want to apply the glow, but I find 1% works great.
What Ryan Church (along many others, I'm sure) likes to do is copy the whole painting onto a new layer, use the glow brush, then erase out the unnecessary parts. You can use a similar setup in Photoshop, but one that's slightly more flexible, I think. Instead of copying the whole painting (shift-ctrl-C), try just creating a new layer, setting it to Linear Dodge, and filling it with black. When you paint on this with the brush described above, the results can be quite similar to the real glow brush. You can erase out of this OR just paint black onto the layer. As an added bonus, you can still modify the painting beneath, and you can also do stuff like smudging and filtering to the glow effects themselves. (Not that that's often a good idea... ) When you're done, you can either merge/flatten the layer down, or you can leave it there and continue to paint above and/or below it. I often leave these lighting effects on their own layer, even in paintings where I'm trying to keep the number of layers down.
Now, the thing that's most different about this is the way you pick colors. In general, to get a similar effect, you have to pick brighter, more saturated colors in Photoshop than in Painter. 50% brightness and 95-100% saturation seems to be a good ballpark to start with if you want the glow to be pretty saturated. And if you want to really go to town with a very bright glow, you may have to change colors as you go, whereas Painter tends to create those colors for you. In addition, you may need to start a new stroke more frequently than with the glow tool, which seems to just keep on brightening as long as you keep a stroke going over itself.
If you like this technique, you can set up this brush as a tool preset so that it'll automatically switch the brush blending mode to Screen. Or, if you REALLY want to go crazy, you can even set up an action that creates a new layer, fills it with black, sets it to Linear Dodge, and then goes to the glow brush tool preset. It's up to you.
I'm sure this is all very obvious to some of you, but hopefully this'll help some people trying to make the switch to Photoshop or who simply like the glow brush like I do. If you've got a better technique, please say so! I intend to post some comparison images soon.