Houdini Output

I’m given several passes of a cg element from Houdini. The include

not sure what the best way to use all of them for compositing. Any help would be appreciated.

I only recognize the first two.

The last two could be point position passes (basically XYZ coordinates for the objects in space where X is red, Y is Green and Z is blue), which are useable in various ways in flame, including a wonderful matchbox that @lewis made (Ls_Posmatte) that allows you to isolate regions of the CG.

Edit, based on this video: https://youtu.be/TlxbcWB-bUI?si=-vmV1xs2s5EYgkUB

AGE appears to be particle age and NOISEp appears to be a way to randomly select some but not all particles.


Hi @Hengy

Apologies if any of this is too obvious.

The main pass you need will be the one called rgba. This is called this because it contains data in the red (r), green (g), blue (b) and alpha (a). This is often called the beauty because it is the combined result of the CG artists lighting and render passes.

This can sometimes be broken down into render passes used to help rebuild the beauty. These are called AOVs (Arbitrary Output Variables). Depending on which render was used you might get passes like Specular or Reflection.

However you have only been given the beauty (rgba) and what I like to call Utility passes. Utility passes like the Z or AGE are not render passes included or required to rebuild the beauty but to be used to help effect the render in some other way.

Z will be your depth pass. Called Z because it contains data for each pixel and represents its position in Z direction. This can sometimes be hard to visualise if this hasn’t been normalised (range of values corrected ) so if it isn’t showing you a black and white image similar to your render you might need to do this yourself. I like to use the 2D histogram.

I feel like this might be a particle render from Houdini so the Z can be tricky to use on fine particles. You should make sure that your beauty has been multiplied by the alpha before applying blur to both the RGB and the A using the Z. Then divide (unpremultiply) the RGB result by the Alpha result before comp.

I often find very little difference between the AGE pass and the alpha from rgba with Houdini particles. Depends how this has been sent up for you.

The thing I find with Utility passes is that you might not need to use them. Unless you have been given direct instructions or you have requested them yourself. They are often included just as a helpful addition.

I like to receive P (position passes) on solid objects so that I can generate depth or direction mattes. Like the Z but in all directions. I break the P into separate R G B channels and use 2D histogram to generate mattes.

TLDR - Unless you have been given direction you might only find use for the rgba and the Z


thanks for the info. Always good to explain completely.