GridImageUpload
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Requirements
Windows and .NET 2.0 for this version, when I get the image compression library compiled for other platforms it will work on Linux and OSX.
Warning
This program corrupts the green and blue channel of images. The effect can be seen fairly easily when uploading low resolution (e.g. 32x32) images losslessly with solid gray boarders around colored blocks. It will look very blurry, despite being uploaded losslessly.
I can't take credit for this discovery. Uchi Desmoulins was the one that tracked the problem down.
The Maya lossless uploader by the same author does appear to upload losslessly without corruption (we tested it).
It can be downloaded from: http://www.jhurliman.org/download/importprimscript-1.0.2.zip
With some work it may be usable as an alternative to this program. The uploading executable itself does not require Maya.