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Using PGMs

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A helpful hint if you are using PGM images with DIRSIG maps. It is orders of magnitude faster to load a binary (aka "raw") PGM than an ASCII one. The difference is especially visible when loading large images, such as 4k by 4k textures in Microscene1.

You can check the PGM format by opening the .pgm file in a text editor. If the first characters in the file are "P2", then you have an ASCII image (notice that all the digital counts are stored in ASCII further down the file). If it says "P5", then it's already binary, so there is nothing left to do.

To convert from ASCII to binary PGMs, you can use the freely available image tool GIMP (www.gimp.org). Simply open the image, select "Save As" and choose "Raw" when it queries about data formatting.

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