Skies are an important compositional element in architectural renderings. Being able to paint clouds and skies from scratch opens up a lot of new possibilities for composing backdrops. Although the technique described here is intended for non-photorealistic renderings, much of it can be used in a photo-realistic workflow as well. This first part will go through the process of creating a custom cloud brush in Photoshop.

There are a lot of freeware and shareware cloud brushes available, but it’s a good idea to be able to create custom brushes when needed.  It’s an easy process and usually worth the extra effort.

Here’s a good example photo to use a base for the brush.  Look for a distinct shape that can be easily isolated from the background.  For this example, let’s keep it simple and just grab the cloud from the center of the image.

In Photoshop, use the Lasso tool to select the central cloud shape.  You don’t need to be especially careful as the blue will go away in the next step.  Invert your selection and delete the background.

With photoshop brushes black is 100% opaque, grays are partially transparent and white is fully transparent.  For this reason you want the brush to be an inverse of what is in the photograph. 

Invert the image via Command/Control-I or Image / Adjustments / Invert and select only the brown-orange color using the Magic Wand tool set to “Color Range”.  For this example, we’ll use a mid-level setting around 100 for Fuzziness - more Fuzziness will create wispier clouds.  Delete the background and all you have left is the cloud.

Turn off all other layers and you can see that it is very transparent.  Go to Edit / Define Brush Preset and type in the name you’d like to use for the brush.  If possible, try to have the brush be 1000 pixels or more in width.  Now you’re ready to paint!

Start with a base color or gradient, and using the brush selector find the new brush you just created.

With the Eyedropper tool, select a warm grey color for the foreground.  Leave the brush set to Normal blending mode with Opacity and Flow at 100%.  Create a new layer above the sky base layer with the default settings (Normal blending mode @ 100%).  Now hit the center of the canvas with the cloud brush and this is what you should get.  It’s not too bad as-is, in the next part we’ll look at some ways of spicing it up a bit.