Re: [Gimp-developer] GIMP's future internal image data format

[Bogdan Szczurek <thebodzio gmail com>]

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 gmail com 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