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I have a grayscale image and I am measuring the luminosity with Photoshop luminosity histograms. However, I would like to know which measurement unit Photoshop uses (e.g. candela per meter square, lux, etc.). I'm new to Photoshop and I did have a look online, but I cannot find this information.

Also, if Photoshop doesn't use candela per meter square, lux, etc., is there a way to calculate candela per meter square from Photoshop values?

Any help will be very much appreciated.

dede
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  • I don't believe they are calibrated to any physical units at all. I think it is just a weighted average of 59% red and 30% green and 11% blue. – Mark Setchell Mar 23 '16 at 20:02
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    Digital images doesn't work that way. Any pixel on an image has a luminosity between 0 and 255 (for 8-bit images), so an average luminosity may have sense, but the effective luminosity (flow of photons) depends merely on the display that shows the image (monitor, TV, etc). In Photoshop one can find the average luminosity of an image by Filter > Blur > Average, but again, this represents the 0...255 intensity level of the pixels. To measure physical luminosity, physical measurement devices are needed. An image (or a picture) doesn't has luminosity, only the device that displays the image. – icefront Feb 08 '21 at 02:49

1 Answers1

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Photoshop doesn't use an actual unit of measurement. It uses percent values that impact on the result.

Marbles
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