[argyllcms] Re: 1st post (improved estimation of blackpoint using a digital camera)
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 09 Dec 2010 18:44:24 +1100
Knut Inge wrote:
I have this nice camera that measure photons quite lineary over a large
dynamic range (3000:1 or so) presented in a raw file. Exposure can even be
shifted to cover different ranges with better SNR, and spatial samples can
be averaged to improve SNR with regards to random noise. Can I use it to
estimate (at least) the luminance-gamma at the bottom of the scale and/or
estimate the error of my calibrator in this respect?
In principle you can. It sounds like a big, expensive project through.
First you would have to characterise the cameras spectral sensitivities -
that takes a monochrometer to do well, or a lot of fancy software
and a ColorCheckerDC/SG to do approximately. Then you have to spectrally
characterize the display (needing a spectrometer), and compute a camera
RGB to CIE XYZ calibration matrix. Then you have to write software to
control the camera and process the resulting RAW file. Then you have
to interface it to the calibration software.
In all, it is probably cheaper and faster to buy a better instrument,
such as the spectrometer you would need to spectrally characterise the
display.
[People have tried some hacky ways of using a camera as a colorimeter,
and even used it on displays - Argyll will let you do that - but
the results are never very good due to the spectral issues, and
it won't work with Argyll's display calibration code, because the
calibration code is interactive - unlike profiling it creates test
values on the fly.]
Graeme Gill.
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