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October 2006
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2006.10.06 22:03 "Inverting color space values in a TIFF file", by Richard Nolde
Tiff list: I'm working a an extension to tiffcrop that will invert the color space of an image. For Bilevel and Grayscale images, this makes sense. I use it to convert a negative microfilm image to a positive one. However, is there a meaningful inversion of a palette color or an RGBA image and would this be done by modifying the palette rather than the data that points into the palette/lookup tables? What sort of algorithm should be applied to the data in the palettes? Eg for 8 bit grayscale, I just subtract the value from 255 and for bilevel data, I just invert the bits with ones complement operator. Doing the same for palette images produces viewable but bizarre images. Instead, should I simply subtract the values in the palette from 255 for 8 bit per color images? I assume an Alpha Channel value would not be modified. My version runs successful on images that have a multiple of 8 bits per pixel and 1 bit per pixel, but I doubt that inverted palette color images mean anything to anyone. Is there any point in allowing such images to be Inverted? Richard Nolde