Radiance colorpict and perforate

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For anyone familiar with the Radiance picture.cal and perforate.cal functions, I have a few questions:

• What are the acceptable file types for picture.cal?
• What other commands exist beside -s that can dimension the perforate.cal pattern? Is it possible to set the distance between objects separately from the object size?
  • What is the relationship between RGB value in the colorpict and picture.cal commands and the transmissivity? It appears that the RGB value that I set in my image file determines the visible transmittance. I performed a simple box study with windows mapped with solid fills at three different RGB values (black, grey, white) and found a somewhat linear relationship between transmittance and RGB value. I would attach an image file visualizing this study but apparently I need ten points to do that...

Thanks in advance for your help and insight.

EDIT: Now that the diagram is uploaded, the RGB values are black (0,0,0), grey (155,155,155), and white (255,255,255) for the image files used with the colorpict + picture.cal function.