Re: `Lossless' retroactive embedding of color profile (avoid JPEG recompression); basic color profile theory
Re: `Lossless' retroactive embedding of color profile (avoid JPEG recompression); basic color profile theory
- Subject: Re: `Lossless' retroactive embedding of color profile (avoid JPEG recompression); basic color profile theory
- From: Graeme Gill <email@hidden>
- Date: Wed, 02 Aug 2006 11:24:14 +1000
Andrew Rodney wrote:
Unavoidable. Anytime you edit a JPEG (and embedding a profile is altering
the data), the JPEG undergoes another round of compression. That's one
downside to JPEG.
That's not always true. There's certainly no technical reason
for a program to re-compress if image data hasn't been altered
(ie., such as embedding a profile). I understand that some
programs are smart enough with JPEG files to deduce the
quantization table used for a particular file, and by default
re-use the same table on compression, resulting in no extra
loss through a decompress, compress cycle. Now I don't
know which (if any) programs are that smart.
Certainly if you continue to open and close (decompress
and compress) the same JPEG file with the same quantisation
table (usually the same program quality setting), then there
is no additional loss for each round.
Graeme Gill.
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