Re: GIMP's future internal image data format

Bogdan Szczurek <thebodzio@xxxxxxxxx> · Wed, 08 Feb 2012 02:06:51 +0100

W dniu 12-02-07 21:43, Martin Renold pisze:

On Tue, Jan 31, 2012 at 06:25:14PM +0100, Bogdan Szczurek wrote:

W dniu 12-01-31 15:48, gespertino@xxxxxxxxx pisze:

Here I have to quote my friend Troy Sobotka who's usually a jerk towards
GIMP :-p but makes a point:
http://troy-sobotka.blogspot.com/2011/01/bit-depth-and-confusion.html

As much as I agree with general idea I want to point out two things
about image comparing 8 bit dithered and 15 bit outputs (the square
regions).

My point was to show the dithering noise that I got rid of by switching from
8bpc to 15bpc.  It wasn't really meant for scientific analysis ;-)

I got your point :). I just expected something "stricter" :). As said 

earlier, I'm not trying to invalidate the reasoning behind 15 bits in 

this case.

First: they're not of the same dynamic range. The upper one is "brighter",
"wider"

Well, I just opened both MyPaint versions and painted roughly the same
(large) number of circles with a faint brush.  The right box is a
magnification of the left box (which is a section of the full circle).

I thought so.

and "not grayscale" like the bottom one.  It makes its "ugliness" more
apparent.

Both images were made with a pure black brush painting over pure white.  The
color that you see comes from the dithering.  I used a different random
number to dither each color channel.  This actually improves the perceived
smoothness of the result.

I'm OK with that, however in this case I've got the impression that 

colors "sticking out" of neutral gray are actually "emphasizing" 

visibility of the dithering (I've did a comparison myself).

Second: why to use dithering anyway since internally you're using sRGB,
monitor "should be" at least sRGB?… Do you have any other examples maybe?

Dithering was done per dab. When you stamp a dab, 8bpc over 8bpc, you get a
16bpc intermediate result.  When scaling this back to 8bpc I used dithering
instead of simple rounding.  If I had done rounding, I would have gotten
banding instead of noise.  Same problem, different manifestation.

Got it :)!

My best!
thebodzio
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