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2019.01.12 17:25 "[Tiff] tiffcp altering image contents (in contrast to what the manual says)?", by Binarus
2019.01.13 17:04 "Re: [Tiff] tiffcp altering image contents (in contrast to what the manual says)?", by Binarus
2019.01.13 18:31 "Re: [Tiff] tiffcp altering image contents (in contrast to what the manual says)?", by Binarus
2019.01.13 19:17 "Re: [Tiff] tiffcp altering image contents (in contrast to what the manual says)?", by Bob Friesenhahn
2019.01.13 21:58 "Re: [Tiff] tiffcp altering image contents (in contrast to what the manual says)?", by Binarus
2019.01.15 20:08 "Re: [Tiff] tiffcp altering image contents - reworded, simplified and with example", by Richard Nolde
[...]

2019.01.13 19:17 "Re: [Tiff] tiffcp altering image contents (in contrast to what the manual says)?", by Bob Friesenhahn

"C:\Program Files\GraphicsMagick-1.3.25-Q16\gm.exe" convert a.tif b.tif -compress jpeg -quality 90 1.tif

If I got you right, GraphicsMagick probably applies the problematic OJPEG compression when executing the command above. We will investigate if we can change that. In the meantime, if our investigations don't lead to anything, could you eventually give a hint regarding an alternative procedure for that first step?

GraphicsMagick uses libtiff to write TIFF so it will never output OJPEG compression. However, since February 7, 2015, GraphicsMagick uses YCbCr encoding when JPEG compression is requested for an RGB image because the resulting file is much smaller. This might be a factor.

By the way, my own email to you was also bounced due a complaint about SPF records but my mail server offers one (unlike the one that Richard unfortunately uses) and so your bounce is the first one I have ever seen complaining about SFP records.

Bob
--
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/

Public Key, http://www.simplesystems.org/users/bfriesen/public-key.txt