Cannot crop mental ray map image clips


Symptom
After cropping a mental ray .map image clip from within the Image clip property editor, the crop effect does not appear in the rendered result (i.e. either in a render region or rendered pic).

Cause
This is not a bug per se, but a by-design situation. The point of using mental ray .map files, is that the image is in fact never loaded into Softimage's memory (except a scaled-down version for OpenGl texture mode). Instead, mental ray memory-maps the image file and only reads the scan-lines needed during rendering. Subsequently, this method does not use as much memory during the rendering process. If the images are large, .map files can also be used to speed up the render process.

There must be enough available disk space to store large and/or many .map files.

Solution
If you decide to use .map files in your production, for best performance, speed and memory footprint, try the following recipe:

  • Permanently crop the images in a 2D application (e.g. Adobe Photoshop or Corel draw
  • Convert the cropped image results to mental ray .map format using the mental ray imf_copy standalone utility, as follows:
Example usage: imf_copy [-v] [-p] inimage outimage [outformat [outtype]]
-v  verbose output
-g  gamma correction
-p  create memory-mappable filtered image pyramid
-e  perform error diffusion
-L  output little-endian .map files
-B  output big-endian .map files

This page was last modified 05:12, 15 Dec 2010.
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