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

Started 2 months ago | Discussions thread
tbcass
tbcass Forum Pro • Posts: 44,595
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

57even wrote:

The human JND for differences in luminance at the level we might typically associate with the mid-tones on a display is about 0.8%.

As we zoom out, the noise level drops because we are no longer seeing single pixels but combinations of pixels with lower average deviation.

Try this - create your own grey patch in PS, then progressively add gaussian noise until you can just see it. Then downsize the image by 50% which will reduce it to half.

A noise level of 0.8% in terms of SNR is about 42dB. Reducing it by half would be 45dB.

A third stop increase in noise, or -1dB, would be noticeable, but 'significant' will depend on your tolerance of course. One stop, or -3dB would be roughly equivalent to doubling the ISO level.

Simply knowing the amount of noise is only half the story. The nature of the noise makes a difference in how effective noise reduction will be on that noise. The more fine grained the noise the easier it is to reduce without smearing detail. I think chroma noise is also more difficult to reduce.

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Tom

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