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TIFF and LibTiff Mail List Archive

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2002.03.07 19:01 "TIFF LAB with JPEG compression", by
2002.03.07 20:15 "Re: TIFF LAB with JPEG compression", by Tom Lane
2002.03.08 13:08 "Re: TIFF LAB with JPEG compression", by Mart? Maria
2002.03.08 12:10 "Re: TIFF LAB with JPEG compression", by vipin aravind

2002.03.08 12:10 "Re: TIFF LAB with JPEG compression", by vipin aravind

unable  to correlate   to  your  problem  but   I had a  problem  with  tiff

jpeg comrpesson.

pagemaker   was  calling  converting  tiff   to   dib  and   the   dib was

sent to compressor

and  the   comrpessed   output   was   sent   to the  printer   and  the

decompression at the printer
simply crashes.
vipin

I've noticed some small problems with TIFF JPEG compression.

I did experiece similar problems on Lab and JPEG. Seems JPEG is not adecuate on such high gamma spaces. If you are using Lab because its color accurancy, you should reconsider the compression scheme. JPEG yelds great compression ratios, but is lossy. And since Lab is hardly perceptually uniform, the noise comes easely evident. A better choice would be to use RGB and embed icc profile. If the profile is accurate enough, you will better results on this way than using Lab.

Here's an odder problem:

   The rightmost two tiles are a bit mangled.

TIFF 6 states that tiles shouldn't hold any alignment. Your image seems somehow dword aligned.

Hope this helps,

Mart� Maria

The little cms project
http://www.littlecms.com
marti@littlecms.com

Hi all, first... thanks for all the great software.

I've noticed some small problems with TIFF JPEG compression.

http://cima.ng-london.org.uk/~john/vermeer_rgb_jpeg.jpg

   One of our vermeers, converted to sRGB and compressed with
   libjpeg.

http://cima.ng-london.org.uk/~john/vermeer_cielab_jpeg.jpg

   The same image, but converted to TIFF LAB and saved with JPEG
   compression. Uncompressed again and resaved as sRGB JPEG.

   Hopefully the red/green mottling in the neutrals is visible.

http://cima.ng-london.org.uk/~john/vermeer_cielab_tiff.tif

   For reference, the TIFF LAB with JPEG compression.

This is all with quality 75, and (I think) fairly recent library versions.

libtiff saves non-rgb images with Y compression for all channels. The jpeg Y compressor does not know that it needs to be very careful around value 128 (a/b == 0), so compression noise is moving things between red and green.

So... am I doing anything stupid, and is there a fix? I guess the best solution would be to tweak the cb/cr compressors for the a/b channels, but I imagine this would be a library change.

Here's an odder problem:

http://cima.ng-london.org.uk/~john/vermeer_tiled.jpg

   This is a 250 pixel across detail of the sRGB image, saved
   as JPEG-compressed tiled TIFF with 128x128 pixel tiles,
   then uncompressed and resaved as a plain jpeg.

   The rightmost two tiles are a bit mangled.

http://cima.ng-london.org.uk/~john/vermeer_tiled.tif

   For reference, the tiled TIFF.

Here it seems to be a multiple-of-8 problem. If you adjust the image width so that the cropped-down tiles on the right and bottom edges are a multiple of 8 across, the mangling vanishes.

Thanks for any advice,

John

========================================================== Aelbert Cuyp 13 February - 12 May 2002

For information and tickets: http://www.nationalgallery.org.uk/exhibitions/cuyp/

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