Re: Subtracting G channel from R and B may increase lossless compression?
- From: "cr88192" <cr88192@xxxxxxxxxxxxxxxxxx>
- Date: Wed, 23 May 2007 07:32:55 +1000
"LiloLilo" <danilo.brambilla@xxxxxxxx> wrote in message
news:46535989$0$21210$5fc30a8@xxxxxxxxxxxxxxxxxx
Hi all,
anybody knows how subtracting G channel from R and from B could
increase lossless compression? I did some tests on some images and found
out that this is true but not for all images. Images with more noise
compress worst.
Do you think that subtracting for example the R channel or the B channel
instead of G would be different?
yes, differencing the channels tends to be fairly effective IME as well (and
as a result, many of my special-purpose image coders have done so).
G makes the most sense since it is the middle of the spectrum and thus
theoretically more closely correlates to the luminosity than do the other
components.
other lossless color transforms may be possible as well (as many argue
yellow more closely relates to the true luminosity, but this is likely more
difficult to deal with losslessly).
can't say with much certainty (I suspect I am partly colorblind anyways, so
my perceptions may be off).
I am not sure exactly why some formats (such as PNG) don't do anything like
this though.
or such...
Best Regards, Danilo
.
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