Prototyping Composition in Photoshop

This blog post is more of a tutorial. We explore ways to composite two rendering passes together. You could just keep jimmying values in your shaders until you get your scene rendering how you like or you could save some time and use a tool like Photoshop to prototype.

Prototyping your composition in Photoshop is mind blowingly easy. First lets reflect what composition actually does, it takes two images and outputs one image comprised of the two input images.

A traditional method of composition is using an additive blend where you just take the color of the two input images and add them together to get your composted image. The code looks like this:

It's dead simple.

Photoshop has a whole list of blending modes that can be applied to layers. To prototype your composition in Photoshop all you need to do is take screenshots of the two images you want to composite, put them in their own layers in Photoshop and cycle through the blend options.

Above are the two images I want to composite together. On the left is my unlit scene and the right is my light.

Here I am applying a divide blend on my two images.

Using different blend options to composite images can create a wide array of different effects.

Here is a multiplicative blend.

The multiplicative blend creates a very dimly lit scene.

And here is a soft light blend, which is what we use in A Case of the Mondays. 

The soft light blend creates a scene with a heavier light influence.

By performing a simple Google search, you can find the mathematical formula to perform almost any blend. Here is the function for a soft light:

From this function, we can easily create a shader which implements it:

It's literally one line of code.

If you cycle through all the blend modes and you cannot find one that you like, your free to make your own. You can play with the opacity levels of the images, the hue, saturation etc. until you create the look you are going for. Then to create your own blending equation, just look at your history in Photoshop and you should be able to derive a shader that performs the effect by looking up each of the functions for the effects you applied and throwing them into a shader.