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February 2008
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2008.02.08 20:44 "Re: 32-bit floating point RGB images (and gamma)", by Chris Cox
Edward; Photoshop by default, reads and writes all 32 bit/channel documents as gamma 1.0. The only way Photoshop would read it as gamma 2.2 is if you included an ICC profile in the TIFF file that specified gamma 2.2 (and then Photoshop would complain because we really want floating point data as gamma 1.0). Now, Photoshop DOES correct for the display -- your gamma 1.0 image will look correct on the display because Photoshop converts the data to the display gamma (and chromaticities) when displaying the image. You might want to read up on color management. Chris On 2/7/08 7:27 AM, "Edward Lam" <edward@sidefx.com> wrote: > Hi Folks, > > What's the best way to express a TIFF file that has 32-bit floating > point, *linear* RGB data? If I do the dumb thing, then Photoshop CS3 > Extended interprets the data with a 2.2 gamma. However, ImageMagick > seems to display the image without the gamma correction. > > Looking at the TIFF 6 spec, the default TransferFunction seems to be 2.2 > gamma correction if unspecified for RGB PhotometricInterpretation? > However, one can't easily provide a linear TransferFunction for 32 bits > per sample data. > > Thanks, > -Edward > _______________________________________________ > Tiff mailing list: Tiff@lists.maptools.org > http://lists.maptools.org/mailman/listinfo/tiff > http://www.remotesensing.org/libtiff/