It’s always quite tricky to work with clouds. We never find the correct sources and most of the time we need to be able to make them move, which means that they have to be on separate layers.
Here is a quick tutorial to give you few tips and tricks.
Let’s start by creating the background. You can start with a proper sky photo without clouds, or you can paint something. In this example, I just painted something with different values, some blue but also some purple. The idea was not being too monochromatic at the start. What’s important is to have nice ramp, nice colors. Be careful not to be too stylized. It has too look reel at the end.
Then, we’ll work on the distant layer. You want to add depth, you want your eye to go through your image and understand the perspective. To add this depth, you need to work on the atmospheric effects, by creating a bit of haze. Feel free to paint a heavy haze, you’ll be able to fade it out later anyway, so don’t be shy. You can ben a little bit the horizon line, it will give you a better feeling as well and the impression you’re high in the sky.
Then, we’ll start to bring the clouds. There are different techniques to extract clouds from a sky, but the easiest way to do it is probably by finding some clouds on a clear blue sky and do a Key. You’ll be able to do it in Photoshop by playing with the Channel and do a selection from the Red one. By transforming this selection into a mask, you’ll be able to keep the cloud.
You need to start with the distant clouds and come closer to your camera. Make sure the scale is correct, and try to follow a realistic way to dress your painting. At this stage, everything is about composition and scale. You need to think about the depth and the way the clouds are in a real sky. Don’t forget to grade your clouds according to their distance to the camera, and be careful of the light direction which needs to always go in the same direction, of course.
You need to vary your clouds. You’ll need a lot of them, otherwise you’ll see that you just duplicated them. Focus on the light which is supposed to travel through your clouds and feel free to add few layers in between your clouds, just to grade them or to add a bit of haze.
At the end, you’ll do a final grade to put the type of color and the amount of haze you’re after. Everything depends on the effect you want to achieve, but in any case, you have to keep everything on layers and adjustment layers so you can change them, address some notes, and make them move.
You can save your layers on different files and do a quick projection in Nuke on cards in order to add a small camera move with a bit of parallax or just some movement in your clouds.