[argyllcms] Re: colprof problem
- From: Marwan Daar <marwan.daar@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 21 Jun 2015 12:21:25 -0400
On 21/06/2015 10:20 AM, Ben Goren wrote:
If you want to know how linear (or not) your camera's sensor's
response is, the way to test is to photograph a subject of known
brightness / reflectivity and compare the values recorded to those of
the scene. The typical way is with a standardized chart, with the
Kodak Q-10 and Sekonic's meter calibration targets being favorites for
this task. I had hoped to finish yesterday and likely will finish
today building a device that I can shine a light into one end, insert
various apertures in the middle, and get precisely-defined
brightnesses out of the other end.
Another way would be to measure the luminance of a display at multiple
gray levels, using a luminance meter/photometer/colorimeter, and then
compare those luminances to the pixel values of RAW images of the same
display.
Advantage is that you can measure at hundreds of different brightness
levels. Disadvantage is that you have the noise level of the reference
meter and potential display spatiotemporal nonuniformities.
With your proposed method, it would be useful to get a very stable light
source. Perhaps a simple tungsten bulb fed with a 5 V battery and a
voltage regulator that keeps the voltage at 3 volts or so. That way, the
light should be very stable until the battery loses almost half its
power (I'm really not savvy when it comes to electronics/electricity
theory, but this method was proposed to me by people who have good
knowledge).
Marwan
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