How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

Started 2 months ago | Discussions thread
Currantos Regular Member • Posts: 306
Correct way

The way you described it is entirely correct and is how we measure noise on a daily basis on our optical machines.

We scan a uniform flat field plastic block without variations and calculate the SD (standard deviation) for the image precisely how you described. If the SD is above a certain value the image is too noisy and machine needs to be recalibrated.

It is NOT possible to get that value on a 'real' image so to speak, that is image with variations in texture, color, brightness, etc. You need to do it on a uniform calibrated value that is known to be a priori and then you can calculate SNR and similar.

So I think that is what the OP should do, shoot gray paper images and compare them.

As to what constitutes significant change in noise, I believe it is logarithmic and not linear so steps of increase get wider as you go up.

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