I’ve been asked about my references to alpha masks and z-depth (or depth cue) with regard to creating renders in Poser, so here’s my run at explaining that. First, an image: This is from the Advanced Render Settings product in the RuntimeDNA store, and is so perfect I could not improve upon it as a visual example. Look at the last two images on the bottom row.
A normal render has a number of aspects combined in the image that we are used to seeing: shadows, ambient occlusion, specular highlights, diffuse color, displacement, and so on. In addition to that, to achieve additional effects, we may need extra render passes. In Poser, I use Semidieu’s Advanced Render Settings product (mentioned above) to do these.
The alpha mat pass generates a black and white silhouette of the selected figure or actor or material, usually a white figure against a black ground. You can bring this rendered result directly into Photoshop as a channel that can then be used to create a selection to assis in your digital painting. I usually generate alpha mats for the human figures (and their clothing and jewelry) in my scenes so that I can more easily paint hair for them, and use the selection generated by the alpha as a guide to erasing stray marks.
The Z-depth or depth cue render pass is also used in post-work, but is a little more complex. This grayscale pass colors the elements closest to the camera white, and in layers going away from the camer, increasingly dark until the furthest (or background) elements are black. I also load this render into a channel in my Photoshop file for the picture and I use it in creating a depth-of-field effect using the Lens Blur command. I do this instead of using the depth of field option in a render because it allows me a lot more control over the result. I do depth of field in images where there really is a lot of distance between the foreground and background as it adds realism to the picture and helps focus (pardon the expression) attention on the important elements of the scene.