On Friday 07 April 2006 03:39 pm, Kai-Uwe Behrmann wrote:
> Am 07.04.06, 22:39 +0200 schrieb Pavel Kanzelsberger:
> > Hi,
> >
> > I'm new to this list... first of all, thanks for this great CMS engine,
> > I'm using it in my application (Pixel image editor).
> >
> > Right now I'm playing with Pantone colors, they're defined as
> > double-floats (64-bit) Lab and I would like to convert them to 8-bit Lab
> > (type_Lab_8)... simple rounding and clipping doesn't work well, maybe I
> > need to multiply those values with some factor but I can't find the
> > right one... any hints please? I see that L=0..255,a/b=-128..127 :)
>
> *L 0..100
From lcms.h
#define TYPE_Lab_DBL (COLORSPACE_SH(PT_Lab)|CHANNELS_SH(3)|BYTES_SH(0))
I have not used this in a transform but I have used
#define TYPE_RGB_DBL (COLORSPACE_SH(PT_RGB)|CHANNELS_SH(3)|BYTES_SH(0))
in a transform to create TYPE_RGB_8 output. It worked just like I expected it
to when I created the transform like this:
xform = cmsCreateTransform(hIn, TYPE_RGB_DBL, hOut, TYPE_RGB_8,
INTENT_PERCEPTUAL, cmsFLAGS_WHITEBLACKCOMPENSATION);
Should work using TYPE_Lab_DBL and TYPE_Lab_8.
>
> > Another thing is that I have HDR images with single float (32-bit) per
> > channel, is there any way to define such type for lcms transform or
> > should I convert it to 16-bit RGB before I want to convert to let's say
> > Lab? I'm wondering if I'm not loosing any precision... as HDR values are
> > in range 0.0 ... 1.0, conversion to 16-bit RGB is then just multiply by
> > 65535, but in HDR there are higher values than 1.0 possible, for
> > example, paper=1.0, sun=549312.0 :)
>
> Lcms is not useful for HDR conversions. The data will be clipped.
> Nethertheless you can do the display transformation with lcms after
> tonemapping.
>
> > Thanks for any answers!
> >
> > regards,
> > --
> > Pavel Kanzelsberger
> > http://www.kanzelsberger.com
> > E-Mail: [EMAIL PROTECTED], ICQ: 209 906 33
> > Jabber: [EMAIL PROTECTED]
>
> regards
> Kai-Uwe Behrmann
> + development for color management
> + imaging / panoramas
> + email: [EMAIL PROTECTED]
> + http://www.behrmann.name
>
>
>
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