[argyllcms] Re: Misc questions about color management

Frédéric wrote:

1) Is it possible to measure the white level of a monitor, in cd/m2 (is it what is calles IRE ?) with argyllcms tools ? 

Yes, spotread will return the XYZ in absolute (cd/m2) by default for
emissive measurements. The Y value is what you're after.

> Is it also possible to have a
direct read of the white color temperature ? 

No. Calculating the correlated color temperature is a somewhat involved
procedure. You basically need to convert the XYZ into u'v' co-ordinates,
and then locate the closest point on the Planckian locus to the u'v' of your
white, when plotted in 2v'/3 space. Some of the details are in the
CIE colorimetry standards. Perhaps a search in Google groups may turn
up some pointers on how to go about this.

2) Does it exist a tool like iccexamin, but which is able to show several ICC profils (2D or 3D) at the same time ? 

Depends on what you mean by "show". If you mean "compare gamuts", then
Argyll has "viewgam", which will convert multiple gamuts (.gam files
from iccgamut or tiffgamut) into a single VRML file.

3) How do I "tag" a jpeg or tiff file with a specified colorspace ? Where is this information stored ? EXIF "colorspace" field for jpeg ? 

Not sure what tools will let you do this (There are none in Argyll, and
details are basically image file format specific.) The details of how ICC 
profiles
are embedded in various image formats is in the ICC specification in Annex B.

4) My Canon 20D camera is able to use AdobeRGB98 or sRGB colorspace when converting to jpeg. This can also be done outside when shooting in Raw. In both cases, what does it mean ? I suppose that 20D colorspace is neither AdobeRGB98 nor sRGB. 

I can't give you any specific information about your Canon 20D, only
general observations. Presumably the camera converts the sensor color
values (which it will have some idea of the colormetric response of),
into the nominated colorspaces. It will (also presumably) apply
whatever processing it sees as "good" to the image data before
it does so (ie. renders the captured data into an output referred
state by setting white points, contrast range etc.)

> So, how is converted the Raw file, say to AdobeRGB98 ?

Using the same steps as above.

> Do prgrams (inside or outside) consider that sensor values *are* in
> AdobeRGB98/sRGB colorspace ?

They should not. The only normal access to the sensor values is the Raw file.

Graeme Gill.



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