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

Started 2 months ago | Discussions thread
drj3 Veteran Member • Posts: 9,423
Re: The Dark Ages got some things right

MrBrightSide wrote:

That's why statistics were invented—so that humans could have some way of determining whether the difference we think we see is real and is the result of something we did rather than just chance.

If you can measure a difference in noise, it is real.  That has nothing to do with whether you are able to see that difference.  I am quite certain that we can measure much smaller differences in noise than what we can see in a photograph.

Statistics could be used to determine how much noise change made a statistically significant visible difference to a specific individual for a specific image of a specific size for a specific kind of noise.  Of course the amount would almost certainly depend on the image content and the specific individual.  It may be relatively easy to see relatively small differences in noise for something like a blue sky, but far more difficult to see differences in noise for an image of a landscape with lots of detail variation inherent in the image.

Statistics—when not being used for evil—are the only defense we have against social, political, environmental, and personal chaos. To get through this world with your sanity and soul intact all you really need are two things: an intro to stats textbook and the Bible. Oh, and a camera.

Mark Scott Abeln wrote:

MrBrightSide wrote:

Which is the exact reason I want to find a way to actually measure noise—the human eye is so easily tricked. I can't afford a program like Imatest though so I'm praying for a solution that already exists in a program to which I have access.

“Statistically significant” doesn’t mean “practically significant”. In photography, lots of folks look at the numbers but slight differences won’t make any difference in the final photograph. For example, you might evaluate strobes, and one model may produce 5% more light than another: that’s measurable, but not photographically significant.

Rather, don’t confuse the means (the camera, software, lenses, etc.) with the ends, that is, producing a good image.

One of my kids has MatLab on his laptop, does that have a noise-measurement component?

Thats what imaging scientists use: or, you can download the free GNU Octave package, which aims to be functionally equivalent to Matlab.

Unfortunately, you have to write the code yourself. It does have the ability to read image files and manipulate them, but it does require serious programming.

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