Search found 22 matches

by Rumpelstielzchen
2014-03-31T12:13:39-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Dear reader,

modifying the "core formula" for the quantization coefficients from "1+x+y" to "(1+x)*(1+y)" -- as "stronger penalty" for hight frequency on both x and y does produce: partially _softer_ images and seems (to me) not be the right way to go further.
by Rumpelstielzchen
2014-03-31T11:46:26-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Dear reader, see below for my latest qtable.pl (cat snippet | base64 -d | bzip2 -d -c ) to compare my qtables; My experience: taking into account the ciede2000 results from above, you'll get - at cjpeg-quality 50 - very slight perhaps better results - even with 1,5 times larger quantization values f...
by Rumpelstielzchen
2014-03-31T05:32:02-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Oh, and well... ciede2000 says something other: If traversing the whole Y/Pb/Pr space and looking for "what's happening when changing one of the three a bit", LittleCms2.5 tells us the following: de00 - Y: 0.292999 de00 - Pb: 0.442875 de00 - Pr: 0.407863 I'm no expert, by my experience says, that Y ...
by Rumpelstielzchen
2014-03-31T05:06:03-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Dear reader, I'll just tought about sensivity on Y, Pb, Pr, and came to the conclusion that rounding Y result in larger errors in R,G,B (by sum(abs(deltaR,G,B))) then rounding of Pb+Pr. (Perhaps it would be worth analyzing this in ciede2000, a (hopefully) more sophisticated distance metric.) So I ca...
by Rumpelstielzchen
2014-03-30T06:11:15-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Well, with this one: http://printtest.eirasys.pt/Testes%20Impressao/Color%20Print%20Test%20Image%2028.jpg At cjpeg -quality 50 / parameter 0.45 of qtable.pl With my qtables: You'll get some loss of detail in the right (compared with cjpeg), deep red flowers (those with the white tips). But the skin ...
by Rumpelstielzchen
2014-03-30T05:47:52-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Hello, Just experimenting around cjpeg -quality 10 "just for fun". Where cjpeg with its qtables generates something like "mosaic pop-art" (pop-art because pink hue shifts on the white wall in the background, the brown chocolate cat gets some more reddish brown, yellow cup gets greenish etc.), with m...
by Rumpelstielzchen
2014-03-30T05:18:04-07:00
Forum: Digital Image Processing
Topic: Better JPEG quantization tables?
Replies: 84
Views: 210861

Re: Better JPEG quantization tables?

Dear Mr. Robidoux, for my portrait shootings with wide aperture I've always wondered about banding in the soft background using strong jpeg compression, and noticed quite often slight hue shifts in skin tones and background. Trying around with dctune2.0 does not give me a adequate result (sorry for ...