[argyllcms] Re: Capture One Profiles
- From: Nikolay Pokhilchenko <nikolay_po@xxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 09 Jul 2013 20:47:08 +0400
9 Jule 2013, 11:36 -04:00 Elle Stone wrote:
>I haven't examined the source code for other raw processors. But the
>dcraw command line raw processor requires white balance information
>before interpolating a raw file. ...
>So you see, the white balancing is done before the interpolation.
Yes. I agree, but I discriminate true white balancing by chromatic adaptation
matrices versus simple balancing of device channel data.
Balancing of raw channels is necessary for succsessfull demosaicing the image
(as I've red about usage of DCRAW). This is interesting problem: the raw
converter needs channel balance for better interpolation. So the channel
multipliers may be changed from picture to picture. On other hand, multipliers
should be constatnt for correct profile operation and correct white balance
correction in CM-software. IMO the best approach is to perform both multipier
balancing for interpolation and the next color conversion and white point
correction in one piece of software - in the color managed RAW converter.
Correct sequence in my opinion:
1. Balancing the channel multipliers for better interpolation, i.e. "white
balancing" the raw data.
2. Spacial computations, including interpolation.
3. Backward application of channel multipliers from the first stage to recover
illumination-depended channel values of interpolated image.
4. Applying the camera profile to interpolated image. At this stage image is
"absolute colorimetric".
5. Correcting the white balance using chromatic adaptation based on mulitpliers
from first point or based on human visual evaluation.
As a result we may get an image with both best interpolation and correct
chromatic adaptation. I suppose this approach is performed in modern DSLRs and
commercial RAW-converters.
>
>On 7/9/13, Nikolay Pokhilchenko < nikolay_po@xxxxxxx > wrote:
>> IMHO about white balancing while RAW to RGB conversion: I think there is no
>> white balancing during RAW conversion if the result is not color managed by
>> the converter. It's just normalization. The normalization to some "standard"
>> image state when typical white in RGB-image is about R=G=B. This
>> normalization is not necessary in general.
>> In color managed workflow the RAW conversion should be done all the same way
>> as while shooting the target. I.e. without "balancing". White balancing
>> should be done after application of camera profile, in color space not in
>> device space. But I didn't know at the moment how to change WB of image with
>> camera profile by means of ArgyllCMS? How to apply certain chromatic
>> adaptation to the image in known color space?
>
>
>--
>http://ninedegreesbelow.com - articles on open source digital photography
>
--
Николай Похильченко
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