Ah layer modes, some artists love them, and some hate them. It can’t hurt to learn how they work, what can hurt, is using them as a crutch, instead of learning how to pick colors yourself. They can, however, make your job much faster!
I’m thinking of doing a whole series on Photoshop tricks, layer modes, layer masks, adjustment layers etc. Here is the first.
It doesn’t replace Photoshop’s help in any way. Read the help, it’s full of useful informations. What is not in the help, however, is how to use these layers in your day to day work.
Multiply makes everything darker, you are never going to get anything lighter with a multiply layer. The darker the layer you use, the darker it’s going to make anything underneath. With some hint of the hue used, but usually, you lose chroma with a multiply layer (compare to the color you paint on your multiply layer, not compared to the layers underneath.) Black is useless in a multiply layer, it will behave in exactly the same way as in a normal layer. I like multiply layers to make shadows, but I usually use a color, not black or grey. It’s especially useful if you are making a shadow on top of something that already has a pattern.
Screen is exactly the opposite of multiply. White is useless in a screen layer, it will behave in exactly the same way as in a normal layer. The same way, black on a screen layer doesn’t show up at all (or white in a multiply layer.)
If you make a layer and fill it with exact medium grey (#808080) and set it on overlay, it’s not going to change anything on your image. #808080 (or I believe it’s 128,128,12) is the exact medium grey. Anything lighter will lighten your layers underneath and anything darker will darken them. So if, say, you take a layer of perfect medium grey, add some noise to it and set it on multiply, you are going to have the noise effect in values, but not in color.
What the heck does one use that for, you wonder. Well, using a layer mask, it means that you can paint in some textures, only where you need them. It also means that you can add some basic shading on stuff that has complex patterns. If you use overlay in cool and warm colors, you can even achieve that AND add the light and shadow colors.
Before you go nuts and use overlay, multiply and screen everywhere, it can be worth it to explore stuff like adjustment layers. I’m especially fond of curve layers and HueSaturationBrightness layers, which I’m going to cover next.