Re: How to incrementally compress jpeg?
Re: How to incrementally compress jpeg?
- Subject: Re: How to incrementally compress jpeg?
- From: Jens Alfke <email@hidden>
- Date: Fri, 20 Nov 2009 14:05:50 -0800
On Nov 20, 2009, at 1:47 PM, Phi Le wrote:
I have an jpeg image and I want to be able to incrementally compress
it using Cocoa/Core Image/Core Graphics. For example, I have A.jpg
(3MB), I compress A and get B.jpg (1MB), compress B and get C.jpg
(400KB), and so on till the image can't be compressed anymore.
What you're doing doesn't make sense; image compression doesn't work
that way. If you JPEG-encode a pixmap, then load it back into an
image, you have another pixmap. Compressing the resulting pixmap isn't
going to result in smaller data just because you decompressed it from
a smaller block of data.
If you want to experiment with progressively greater and greater
compression levels, you have to start with the same source pixmap
every time and gradually decrease the compression factor. (For
example, I did this in iChat to compress the user's buddy icon down to
under 2K to fit in a Bonjour record. There's a loop that keeps
increasing the compression factor until the data size is small enough.)
—Jens_______________________________________________
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