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Subject: Re: ACR Calibration





The dcraw –m option says not to convert the camera RGB space. Thus, >unless
you know the characteristics of the camera RGB space, you >don’t know
the precise meaning of the values.




But I'm not looking for color meaning in this step but sensor exposure.

In addition, setting exposure based on the white patch is not very >reliable.
The “neutral 5” patch is photographic middle gray (18%). >This works out
to 127 for Adobe RGB or sRGB or to 110 for ProPhoto >or ColorMatch RGB.
Middle gray is the basis of photographic exposure >metering and ISO settings.
Neither black nor white is specifically >defined in terms of density on
the CC chart.




But this change the suggested process. Gretagmachbet write in Profilemaker manual: the correct exposure of the testchart should lead to RGB values 235-245 for the white patch, is wrong for you?

The camera color space (after ADC) is typically gamma 1 (a so-called >linear
space). Thus the values would have lower numbers than in a >1.8 or 2.2
gamma color space. The image is darker.




Yes my images are very dark but the white patch value is 240

Second doubt: is important the number of many lux of light drop on the chart?

I'm very confused :-(
Why Adobe don't write a FAQ on this very confused treatment?
Thanks Rags

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