I've come back to finish the diffuse map (texture) for my brick wall, following the tutorial in my book. To begin with I painted my own texture layer for the mortar in between the bricks using a combination of paint brushes - but no photographs/ready-made texture images as I want to avoid this as much as possible for this project. I want to create all the textures, where possible, from scratch.
The next thing to do is switch the blend mode for the ambient occlusion layer (I added the ambient occlusion I made to this Photoshop file) to Multiply. This means that only the black values of the layer are visible above the layers below it, meaning the shadows from the AO remain visible.
Then I created a brightness/contrast adjustment layer for the Mortar. The purpose of an adjustment layer is to enhance the selected layer in some way, without permanently affecting the layer itself.
To make the texture for the bricks, I started with a copy of the Mortar layer. This is nested into the Brick Mask layer (the white 'bricks only' layer I created previously) which means that it is only visible where the Brick Mask layer is visible, and it is invisible where the Brick Mask layer is clear of pixels. I created brightness/contrast and hue/saturation adjustment layers for the Brick so that I could alter the copied layer to make it stand out from the Mortar layer.
I then made another painted texture layer which is the Colour_Variation, this creates some different scratches and patterns to make the Brick appear different from the Mortar. On top of that I added the Colour layer, which is simply filled with a dark red solid colour and the blend mode changed to Overlay so that this colour is applied to all the Brick associated layers.
In it's own layer is Grime, which is a black and white gradient fill, with the blend mode set to Multiply and the layer Opacity lowered to 35%. This makes it appear as though the wall is darker at the bottom, which is naturally where a wall gathers more dirt from the ground on its surface. Many of my model textures will need to have a layer like this, as I want them to look quite aged and dirty.
Finally, to give the texture a little more variation, I created a couple of adjustment layers on the AO layer. I selected bricks at random with the marquee tool and adjusted their brightness/contrast to make them stand out from the rest of the bricks. On one of the adjustment layers I made the bricks darker and the other, lighter. The last step is to create a Final layer made up of a merged image of all the visible layers. I saved this as a Targa to be applied to my wall plane in Maya.
