Mailing Lists: Apple Mailing Lists
Image of Mac OS face in stamp
 
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Color reduction

On Tue, 15 Jan 2008, Scott Ribe wrote:

PNG might be the right format. JPEG will have ringing artifacts with
simple line art like that.


I'll look at PNG. I also plan to try TIFF + zlib, and even making an
uncompressed TIFF then bzip'ing it. In some experiments, I got surprisingly
good results with JPEG. I can't of course use a heavy degree of
quantization, but I was surprised at how much compression I could get before
artifacts started showing up. I think part of it is that with scanned images
the edges are already slightly "softened" by the aliasing inherent in the
sampling, as opposed to a computer-generated original where many edges may
be absolute.

A compression format based on a wavelet transform of the whole image ought to do significantly better than JPEG, because the images in question do not have large areas with texture. Wavelets typically remove much more redundancy from large uniform areas, while JPEG cannot look past the 8x8 pixel tiles that it transforms independently. The amount of ringing can be controlled by the type of wavelet used. But even the "standard" Daubechies filter pair with 9 and 7 taps (also called "4,4" refering to the number of "vanishing moments" in each filter) handles line art surprisingly well.

  Holger
_______________________________________________
Do not post admin requests to the list. They will be ignored.
PerfOptimization-dev mailing list      (email@hidden)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/perfoptimization-dev/email@hidden

This email sent to email@hidden
References: 
 >Re: Color reduction (From: Scott Ribe <email@hidden>)



Visit the Apple Store online or at retail locations.
1-800-MY-APPLE

Contact Apple | Terms of Use | Privacy Policy

Copyright © 2007 Apple Inc. All rights reserved.