Legacy ImageMagick Discussions Archive

Well, now somewhat more psychedelic:

Original (some dots with pixel text of varying contrast):

http://s30.postimg.org/lf271rr1t/ori.png

Target size: 23040 bytes (1/40).

Lurawave JP2 Irfanview:
http://s13.postimg.org/3k6hmx4cn/lura.png

Kakadu 7.4 with -precise:
http://s24.postimg.org ...

Dear Reader,

Here I'm trying to find out some charactaristics of jpeg2000 en/decoder: Lurawave JP2 Plugin for Irfanview, Kakadu (current version), Openjpeg 2.1.0.

Here my test image (somewhat synthetic, with small @ with different contrasts):

http://s23.postimg.org/51brt8y6j/patch.png

Target ...

top left triangle: my (jpeg) quantization tables,
stripe below: kakadu jpeg2000
stripe below: openjpeg(2000)
stripe below: jasper
and then the same sequence down again.

I've made some tests with irfanview jp2-Plugin (luratech) export (max. 640x480): kakadu is better - but luratech is still far ...

For the interested:

I've compared the original with
1. my quant. tables with
2. kakadu jpeg2000 (commercial)
3. openjpeg 2000 2.1.0
4. jasper (ubuntu 14.04)

Here the result (the less colourful stripes: myquant + kakadu)

Mea culpa... the "my quantization tables" was using (x^2+y^2+10) as base formula ...
here now the right one with (x+y+1) (slightly better than above formula)

http://s29.postimg.org/q4ol835pj/myq.jpg

Difference between original vs cjpeg -q 28, my quantization tables
, optically enhanced:

http ...

Well, here an example, to illustrate "what I'm talking about".



Original image from Petr Kratochvil, http://www.publicdomainpictures.net/ sized down using
convert kratochvil.jpg -resize 535x800 ori.ppm

Original (cjpeg -quality 100):
http://i59.tinypic.com/20svpqt.jpg

Target size: 26809 bytes ...

Dear reader,

I've often read something like "use 16 bit depth with ProPhotoRGB to avoid color banding".

Well, my question was "how more worse than sRGB is ProPhotoRGB at 8 bit"?

here the short answer:
AdobeRGB1998.icc: max CIEΔE2000 1.644989 at <29.882812 29.882812 31.875000>, direction <0 1 0 ...

Still comparing with "state of the art" (?) dctune2.0 and my opinion is still that dctune2.0 - even with correct dpi and viewing distance - produces, using the previous mentioned http://www.dpreview.com/PrinterReviews/1107allinoneprinters/images/Kodak-sRGB.jpg scaled down to 1600x... at 250 KB ...

Subsampling: Tried ciecam02, forget about it, you would have to create rgb values, that after the "wrong" RGB -> YPbPr and back - would still be "fitting".

For the interested:
DCtune2.0 produces some interesting results, but still has problems with skin colors (reddish spots etc.) in my opinion ...

Yes, this way seems to work:

Do LinearRGB->YPbPr, subsampling chroma manually, ubsampling, reconstruction of sRGB,
Feed this into convert/cjpeg.

EDIT: perhaps chroma subsampling should be done in the C,h of the ciecam02 (think polar coordinates -> cartesian, this to subsample) insted of YPbPr ...

According to "YPbPr conversion should be done from linear RGB-Space instead of sRGB":

I've compared this manually this way (if someone else wants to try):

#!/bin/bash

# JPEG: Still Image Data Compression Standard
# von William B. Pennebaker,Joan L. Mitchell
# Sec. J.1.1.2: Bi-linear ...

Dear Reader,

I've found some very interesting aspect due to RGB => YPbPr here:

http://sas-origin.onstreammedia.com/origin/smpte0109/New%20Folder%201/Chan.pdf

sRGB should have been linearized (think photons) first before matrix conversion to YPbPr.

EDIT: this can't be done with jpeg, as far as I ...

Same filesize as your quality75 - Table:

with sqrt(1+x²+y²)-Kernel (the (1+x+y) kernel is not much a visual difference):
5 7 11 15 20 25 30 34
7 9 12 16 21 26 31 35
11 12 15 18 23 27 31 36
15 16 18 22 25 29 33 37
21 21 22 25 28 31 36 40
25 26 27 29 32 35 38 43
30 31 31 33 35 39 42 46
34 35 ...

Dear Juce,

after taking a first look at your f(x) using gnuplot my first tought was: -cos(pi*x).
But it has a lower f'(x) near 0 and 1

What do you think about different tables for Y, Pb and Pr ?

Kind regards,
Jochen

Dear Mr. Robidoux,

I've tested your first table of this thread, 2012-02-21T21:46:52+00:00

Your qtable results in somewhat more sharpness at expense of color reproduction.
(spatial resolution vs color granularity)

(as expected)