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: Thu, 03 Aug 2006 00:26:18 +1000
Andrew Rodney wrote:
But they do change. So what about doing this over and over again but instead
of JPEG, use PSD and TIFF?
If you don't want to understand how things work, then fine.
Some people would like to use the right tool for the right task.
For those interested, the point is that the subsequent changes
are minor (ie. probably not visible), and ultimately stop all
together.
To quantify it, if I use quality 4 in photoshop with my test image,
then on the first save to jpeg 49% of the pixels change value, with
an average change of 0.7 bits.
Between the first jpeg and the 6th, 1.64% of the pixels change value,
and the average change is 0.03 bits. After the sixth save, no
pixels change value.
So the idea that decompressing and compressing a JPEG degrades the
image each and every time, is a myth.
Graeme Gill.
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