Sent: 2011-12-23 10:51:01 UTC (5 months ago)

From: Alexander Hämmerle

Babl CMYK-conversions

permalink

Hi,

there seem to be some quirks in babl.

1) ./babl/base/model-cmyk.c

In the cmyk_to_rgb-function the components are assigned from the source in an
erroneous order. Obviously in the CMYK-colorspace magenta is the second color.
Here yellow takes its place and magenta is the third one.

double cyan = ((double *) src)[0];
double yellow = ((double *) src)[1];
double magenta = ((double *) src)[2];
double key = ((double *) src)[3];

2) ./babl/extensions/naive-CMYK.c

For what reason is there a second implementation of essentially the same code
as you find it in model-cmyk.c in the file naive-CMYK.c? The only difference
seems to be that model-cmyk.c makes the conversion RGB->CMYK and naive-CMYK.c
implements RGBA->CMYK.
Wouldn't it be more comprehensive to have it all in one place? Or is RGB->CMYK
the more basic conversion? I thought in Babl the RGBA-space were something
like a reference.

3) More stunning for me: model-cmyk.c exists only in the GIT clone from
git://git.gnome.org/babl but not in the downloaded tar.bz2 from
ftp.gtk.org/pub/babl :-?

Sorry for my lack of understanding,
Alex

Sent: 2011-12-23 11:53:18 UTC (5 months ago)

From: Øyvind Kolås

Babl CMYK-conversions

permalink

On Fri, Dec 23, 2011 at 10:51 AM, Alexander H

Sent: 2011-12-28 17:19:01 UTC (5 months ago)

From: Alexander Hämmerle

Babl CMYK-conversions

permalink

On Friday 23 December 2011 12:53:18 you wrote:
> Thank you for your observation. The naive-cmyk extension is the only
> one that should be there. As CMYK conversions go it is not good enough
> either which is why it is called naive (that implementation seems to
> have the correct component ordering as well). An extension that
> implements conversions through ICC profiles and perhaps lcms would be
> a more proper way to define a CMYK based color space and pixel format.

I'm very interested in a more ambitious implementation of the CMYK-colorspace.
Also because I would like to do more experimentation with printed outputs of
processed or otherwise created images. Do you have any suggestions for a good
introductory work on the theory related to ICC-profiles and digital color
management systems?

alex

Sent: 2011-12-28 17:20:28 UTC (5 months ago)

From: Alexandre Prokoudine

Babl CMYK-conversions

permalink

On Wed, Dec 28, 2011 at 9:19 PM, Alexander H

Sent: 2011-12-28 18:27:52 UTC (5 months ago)

From: Øyvind Kolås

Babl CMYK-conversions

permalink

On Wed, Dec 28, 2011 at 5:20 PM, Alexandre Prokoudine
wrote:
> On Wed, Dec 28, 2011 at 9:19 PM, Alexander H