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 15:22:08 -0800
On Nov 20, 2009, at 2:20 PM, Phi Le wrote:
A = new Image(data)
B = A.save(JPEGType, 0.5)
C = B.save(JPEGType, 0.5)
where the sizes A > B > C and the deltas are significant. I can do
this if B is saved to disk and reload back.
Weird — the save method must be looking up the original compression
factor from the JPEG metadata and then multiplying your requested
scale factor by that. I would think that would be the wrong thing to
do most of the time: if I write some code that takes an image object
and wants to save it to disk as a JPEG, I want to be able to specify
the compression factor to use without having it be based on the pre-
existing history of the file the image came from.
So if I am given an NSImage, but not the backing NSData directly, can
I ask the NSImage, NSImageRep or something else to give me information
about the original data, filetype, compression factor ?
I don't think the NSImage retains that amount of information about the
source of the image. You might be able to use Quartz's CGImage APIs to
do something like that, though.
It would be a lot easier to take a single image and just repeatedly
convert it to JPEG with decreasing compression factors.
—Jens_______________________________________________
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