Hi,
I'm afraid you have to measure the illuminant using a colorimeter or spectrophotometer anyway... Also note not all illuminants have chromaticity on blackbody locus. Having the xy coordinates, the function _cmsIdentifyWhitePoint() would give you an approximate temperature. Then the origin temperature would be that one used in the original input profile and dest would be the temperature of new illuminant.
Regards, Marti.
----- Original Message ----- From: "Dirk Str�ker" <[EMAIL PROTECTED]>
To: "Marti" <[EMAIL PROTECTED]>
Cc: <[email protected]>
Sent: Tuesday, March 01, 2005 9:29 PM
Subject: Re: [Lcms-user] White balance
Hi,
first of all thank you both for the quick and informative answers.
It is clear, that I get the best results with individual profiles for every
illuminant, but I fear, I have to deal with the common behavior of the people
working with microscopes and CCD-cameras doing this "white balance" on the
illuminant. I got to find the best realizable solution and accept the lower
precission. It will still be a great enhancement of the color quality!
I think, we will try Marti's "quick and dirty"-solution, but how do I estimate
the value for the TempSrc in �K? What I have are RGB-values, which are
normally not equal. They should be my input white point, which I want to be
mapped to R=G=B at the end. Additionally I can't be sure, that they lie
exactly on the line of temperature dependent white points (I do not know, how
this line is called). And what are my TempDest-values, how can I calculate
them?
Regards Dirk Str�ker
Hi,
I fully agree the good solution is to have a different profile for each illuminant, as that would be the *only* way to get decent results.
However, there is a quick hack to do if you really don't care about
precission.
Again, Hal has suggested what is the "good" way, and what I am here stating
is
just quick and dirty, but anyway here we go:
There is a specialized, virtual device link profile for doing some specific
tweaks.
One of those tweaks is white point translation.
cmsCreateBCHSWabstractProfile(int nLUTPoints, double Bright, double Contrast, double Hue, double Saturation, int TempSrc, int TempDest);
Keep Bright, Hue and Saturation to zero. Keep Contrast to 1, and set TempSrc and TempDest as the temperatures in �K of input and output white points. That function would give you a abstract devicelink handle. Do a multiprofile transform joining input (microscope) profile, that one and finally sRGB (or whatever output).
Regards, Marti Maria.
----- Original Message ----- From: "Hal V Engel" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, March 01, 2005 2:23 AM Subject: Re: [Lcms-user] White balance
Dirk,
As you have found out when doing color profiles for a device everything in
the color processing chain matters and has an impact on the resulting
profile. A different light source or a light source adjusted differently
will change the profile. As a photographer I do not expect my day light
camera profiles to work with photos that were shot using tungsten light.
So I have profiles for my camera for each type of light that I might shot
with as well as for each film type. On some occasions I may shot a custom
color target for a specific shoot because I am not sure of the lighting.
So there is no easy answer as you can not reasonably expect a profile that
is created using one device to work perfectly for another similar device.
Let alone for
a similar device with the light adjusted differently.
This all boils down to having a consistant workflow so that you can
reproduce
the same results consistently. Since my situation is such that I only
have to deal with my personal workflow this is not a big issue. I
understand how important this is and I always follow a consistant routine
so that my results
are reproducible. It sounds like you are dealing with others that may need
training to understand how this works and how their workflow influences the
results they get. In addition it may require that you have a number of
profiles that are correct for different devices and conditions.
Hal
On Monday 28 February 2005 01:22 pm, Dirk Str�ker wrote:
> Am Montag, 28. Februar 2005 22:18 schrieb Dirk Str�ker:
> > Hi everybody,
> >
> > I have a problem, which might is simple to solve, but in the moment
> > I'm a bit confused and can't find a simple answer.
> > Before I explain my problem I will give a short description of my
> > setup. I'm working with a CCD-camera on a microscope. The color > > quality
> > of the system was very bad, so I did some research, found > > ICC-profiles,
> > color management...and so on (I learned a lot in the past weeks ;-)
> > ). We bought software from Gretag MacBeth to create profiles for the
> > cameras
> > and we were pretty impressed over the results. After that we found
> > "littleCMS" and tried to use it to achieve the improved color quality
> > directly, which worked fine.
> > The problem is, that it is a common technique, to make a so called
> > "white
> > balance" on the "illumination", the yellowish ligth of the tungsten
> > halogen lamp should be white or gray (R=G=B). I understood the ICC
> > color-management-technique in that way, that this is normally done by
> > the
> > chromatic adaption tag (often the "Bradford matrix"). This is matrix > > is
> > calculated while creating the profile.
> > But not every individual microscope lamp is the same. Some people dim
> > the
> > lamp, or the lamp is older... but everyone wants to make the pure > > lamp
> > light gray.
> > How can I do this
>
> Oops, I wasn't ready.
>
> Should I use "cmsCreateRGBProfile" and make a "transform" with the
> "normal"
> camera profile + the new RGBProfile?
>
> Maybe there is a simple solution and I'm just to blind to see...
>
> I hope my explanations weren't to confusing ;-)
>
>
>
> Dirk Str�ker
>
>
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