1997.05.01 14:24 "Re: tiled-pyramidal-LAB-JPEG-TIFF", by Tom Lane
- I'm using PHOTOMETRIC_CIELAB, and COMPRESSION_JPEG. Does the JPEG layer know about LAB, ie. does it replace its RGB->YCC conversion with something more appropriate? I'm getting some sightly funny effects ...
tif_jpeg.c just turns off all color conversion and downsampling if the photometric tag is anything but YCbCr. I'm pretty sure I tested that case (using PHOTOMETRIC_RGB) but would not want to swear there are no bugs in it. What are your "funny effects"?
With the current tif_jpeg code, LAB will not be compressed as efficiently as it could be, because all three channels will be compressed at luminance quality. A and B ought to be compressed at chroma quality, I believe. They really ought to be downsampled, too, but that's forbidden by the current TIFF 6.0 spec (because the subsampling tags are defined with respect to YCbCr only). This is an oversight that I hope TIFF 7 will rectify.
I was planning to revisit the code once TIFF 7 was out (Adobe sometimes makes noises about a new draft), and make it know about LAB specifically. But if you want to get in there sooner and hack on it, go for it.
regards, tom lane
organizer, Independent JPEG Group