View Full Version : how to creat a matte channel in Houdini
05 May 2011, 06:57 AM
How to creat a matte channel in houdini? where could i find good tutorials for render pass?
Use the default materials in the Material Palette first of all. They have all the default export planes set up for you.
Next in the output driver Mantra ROP, in the Properties > Output tab, create as many Extra Image Plane outputs as you need.
There are a lot of default exports now available in the menu arrow to the right of the VEX Variable parameter (the parameter that is set to the export variable name defined in the surface shader).
For direct diffuse samples, choose Direct Diffuse
For indirect diffuse samples, choose Indirect Diffuse
For all diffuse lighting samples, choose Combined Diffuse
For direct diffuse without shadows, choose Direct Unshadowed
For indirect diffuse without shadows, choose Indirect Unshadowed
There is even an option to generate these passes per light in the Light Exports parameter option in each export plane. Very handy if you want to break down the passes per light. This includes any environment lights.
Rendering to ip will spawn mplay and you can view all the image planes in the top left menu that defaults to "C".
If you render to disk, render to exr (OpenEXR) if you can (not using Apprentice or HD) for comp in any compositor and have the embedded image planes. If you are Apprentice then you are limited to rendering to our .pic format which is fine. It too can hold all your image planes at all the supported bit depths. Both formats are supported by Houdini's compositor.
I usually set the bit depth for each extra image plane to 16 bit float (commonly referred to as "half float") as that is usually enough for comp later on.
In both Mplay and the IPR render preview window, you can use the image plane menu button to view all the various exported extra image planes.
I would have attached a file but I have exceeded my upload limit. I have unlimited uploads on OdForce and SESI forums. I need to talk to the cgtalk forum manager to see if I can bump this up...
For a good introductory tutorial on exporting Light passes, please see the vimeo tutorial by Peter Quint here:
To generate per object matte channels, you can export the Node ID channel. Each object in your scene will be given a unique id. The numbers can be all over (render id objects can be).
In mplay, you can hit the adapt to full range button to see the range. Given that object id's start at 0 and can go as high as 10000 or more, your image will appear completely white. Adapt to full range will reset the white and black points to encompass the entire color range in the viewer.
You can hit the "i" hotkey to inspect the values as well.
In comp, you can easily do a color extract on that id color value to extract that mask. You can then use that comp channel as a mask or multiply in to the image to extract that object. What makes this handy is that you carry all the masks for each object in the single image without having to do per object passes.
In PBR (Physically Based Rendering) workflows, you really want to render the entire plate in one go to capture all the indirect bounces between objects making this workflow a decent one.
In Microply/Raytracing workflows, you can fall back to the per object output render passes by adding a Mantra ROP output driver for each object and wire them together and press render on the last one to auto create all the passes for each object.
There are other ways to extract object masks as well. If you can describe in more detail what you are doing, it will help in giving the best answer.
05 May 2011, 03:14 PM
05 May 2011, 03:56 AM
thank fomal 4 good link!
i just understand a part of render pass!
But rjw, i really dont make image Extra image plane work ! all image out is black and no matte!
05 May 2011, 04:53 PM
upload a file! It sounds like it could be just a typo or something. :)
a friend gave me this file a while ago which might help, but it only uses 4 colors.
05 May 2011, 04:53 PM
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