Hi David,

David Gómez wrote:
> I've scanned some jpeg images with a 24bit depth. Some of them are old
> photographies in black&white that show 'bands' when are displayed on
> a 16 bit depth display.

This is a normal phenomenon when moving to higher bitdepths.
Unless you're talking about 16 bits in total, and not 16 bits per
channel, in which case I'd be a bit mystified...

> After digging in the menus i noticed that the
> image could be transformed to a indexed pallete, with a Floyd-Steinberg
> dithering, but that did not solve nothing, the maximum number of colors
> cannot be set to more that 256 :-/.

Floyd-Steinberg dithering is basically a way to approximate more 
colors with a smaller palette... it does not actually do anything
like what you are expecting (as you have noticed).

> Is there another way to dither an image in gimp?

Have you tried blurring the image with a radius of 0.5 or 1.5
pixels? This sometimes works quite well.

> Programs like gqview, an image viewer, use the dither
> algorithms bundled with gdx_pixbuf in gtk2, and they work perfectly with
> the same images. Why cannot the gimp do the same quality dithering if
> it's using the same library?

Oh, I see what you mean, I think - you're talking about the
rendering of the data, you don't actually want to change the
underlying data, you want it to look better. Is that right?

If that's the case, then I'm afraid the answer is that I don't
know. I thought we used a GdkPixbuf, so if we don't I'm stumped


       David Neary,
       Lyon, France
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