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

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MrBrightSide
MrBrightSide Contributing Member • Posts: 748
How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

Failing that, what other simple methods are there to measure noise in digital photos.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Question 3:  There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

photonut2008 Veteran Member • Posts: 4,962
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

MrBrightSide wrote:

Question 2: Once the noise is measure[d,] what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Think stops rather than percentages. I think a third of a stop wouldn't be very much because in practical terms you can open up your lens or slow down your exposure time by that much and it is rarely a dealbreaker. A stop is 50% less or 100% more, which may seem like a lot, and given what I just wrote it clearly is a lot (having to double your exposure often pushes the outer boundaries of what would be acceptable), but keep in mind that we do not see things linearly, so if the light level is doubled your eyes will simply adjust to that and you won't feel like it's twice as bright as it was before even though it is measurably twice as bright.

Working from the above logic, I would say half a stop is a significant enough difference to matter once you are in the higher ISO range, but that begs yet another question:  What constitutes higher versus medium ISO? That will depend on your output size and your format. A smaller output size with a larger format probably does reasonably well at ISO 6400, but a larger output with a smaller format probably doesn't do as well at ISO 1600. The bottom line then is that it's all relative.

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FingerPainter Veteran Member • Posts: 8,363
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?
2

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools

yes

in Photoshop

I'm not so sure about that. I am unaware of Photoshop having a facility to calculate and report the SNR of a photo, but my familiarity with PS is limited, so don't take that as a definite assertion that PS cannot do it.

to measure the noise in a photograph.

The usual measurement for noise in a photo is Signal to Noise Ratio (SNR), expressed in decibels (dB). The SNR of images taken with modern digital cameras tends to track the square root of the exposure (in lux seconds) closely.

There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

PS can recognize noise and treat it because noise is variation in pixel values. It can treat the problem locally without calculating the magnitude of the problem over the whole image.

Failing that, what other simple methods are there to measure noise in digital photos.

If it was both simple and useful, I'd expect it to be a common tool in photographic development software.

A program more likely to be able to calculate and report SNR would be RawDigger.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

A 3dB difference, which represents the change in noisiness related to a change of 1 stop of exposure, can often be detected by the human eye, but perhaps not without pixel peeping.

Question 3: There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

I'm not sure it is wise to assume everybody has your level of tolerance.

photonut2008 Veteran Member • Posts: 4,962
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

FingerPainter wrote:

MrBrightSide wrote:

to measure the noise in a photograph.

The usual measurement for noise in a photo is Signal to Noise Ratio (SNR), expressed in decibels (dB). The SNR of images taken with modern digital cameras tends to track the square root of the exposure (in lux seconds) closely.

Measurement of S/N for some part of the scene which will have a range of signal strengths that constitute the dynamic range (DR) of the scene.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

A 3dB difference, which represents the change in noisiness related to a change of 1 stop of exposure, can often be detected by the human eye, but perhaps not without pixel peeping.

It could also be expressed as a lost stop of DR. How many stops of DR that you can afford to lose before the primary subject and important shadow detail are starting to be buried in noise depends on the camera model (and or any cropping), the output size, and to some degree subjective and personal considerations.

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57even Forum Pro • Posts: 14,110
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

Failing that, what other simple methods are there to measure noise in digital photos.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Question 3: There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

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.

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D Cox Forum Pro • Posts: 24,641
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

57even wrote:

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

Failing that, what other simple methods are there to measure noise in digital photos.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Question 3: There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

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.

Monitor settings and ambient light will affect how visible the noise is.

sybersitizen Forum Pro • Posts: 14,871
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph.

I'd be interested in reading such a thing. Because the statistics count the pixel values in the image, I assume you would want an image with no features - one that theoretically should have just one perfect pixel value throughout. Then you could judge noise content by checking how far the actual pixels vary from that norm.

There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

I don't think my version of Photoshop (CS3) noise reduction identifies noise. It just identifies local differences in pixel values and makes adjustments to them based on some set rules and according to my input.

Failing that, what other simple methods are there to measure noise in digital photos.

I dunno.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

I dunno. Neither 1% nor 10% sounds significant to me, but 100% does.

ken_in_nh Regular Member • Posts: 272
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

I think you may be thinking of the long gone scientific version of Photoshop, which had a generous set of measurement tools built in, but none for formal noise measurement IIRC.

Failing that, what other simple methods are there to measure noise in digital photos.

No simple way to measure noise. In electronic circuits, noise is typically measured (if it's measured at all these days) using standardized signals - usually from a tone generator which generates a pure sine or pure square wave, although with the latter, you don't measure true noise, but ringing and such instead.

In photography, you'd measure noise with a very uniform grey scale, and measure it at different light intensities. But why?

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

You're thinking about it the wrong way. Outside scientific imaging, and go to Edmund's Optics (https://www.edmundoptics.com/ ) if you want to learn more about that, photography is largely perceptual, artistic if you will.  This means that one's reaction to noise in an image is both highly subjective, and variable depending on the scene and artistic intent.  That's why grain, a kind of noise, is a plus in some images.

knickerhawk Veteran Member • Posts: 6,525
Here's what you can do in PS
8

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

There is no direct, objective/statistical measurement of noise in PS. However, there is an indirect objective measurement that provides some useful insight into noise. You can use the standard deviation measurement that appears in the histogram tool to compare uniform patches that don't have any detail. A good example is the gray patches in the GretagMacbeth chart in the DPR studio scene. Since we know that those patches are highly uniform with no intended detail, deviations in a spatial measurement of the patches is highly indicative of noise. Thus, a higher standard deviation score for the same patch under same exposure conditions is objectively measurable evidence of the difference in the amount of noise. For example:

The Std Dev for the selected region of the ISO 400 shot is 4.42 here. Note the steep relatively "thin" and lined up peaks in the histogram itself.

With the selection moved down to the ISO 3200 patch, the Std Dev score is significantly higher (12.67) and the shapes of the humps in the histograms are also spread out. Thus, we have an objective score and an objective visual representation of the difference in noise between the two patches.

While the Standard Deviation measurement in PS is useful, it should be used with caution, especially when comparing areas that are not known to be identical. Also, other image factors (such as detail and color) can be confounding, and even minor and difficult to detect differences in processing can significantly affect the usefulness of the standard deviation score as an objective noise measurement.

Failing that, what other simple methods are there to measure noise in digital photos.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Question 3: There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

tbcass
tbcass Forum Pro • Posts: 44,591
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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Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 14,350
Linear

The numbers from this technique would be more reliable if the image is first converted to a linear color space, otherwise the gamma correction would confuse the results.

Demosaicing, noise reduction, and conversion to JPEG changes the results as well, as does lens correction. While it may be important to know how these processes modify noise, it will make the results far harder to interpret well.

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57even Forum Pro • Posts: 14,110
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?
1

D Cox wrote:

57even wrote:

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

Failing that, what other simple methods are there to measure noise in digital photos.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Question 3: There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

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.

Monitor settings and ambient light will affect how visible the noise is.

Yes, which is why the 0.8% figure is for a typical monitor at default settings.

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57even Forum Pro • Posts: 14,110
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

tbcass wrote:

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.

It depends which raw processor you use. This is not a product of the sensor, only the software you use to demosaik it. Adobe, C1 and Silkypix have different default noise levels, and all add sharpening and NR to the data.

But the JND is the same, whatever. So, if the noise level is 0.8%, increasing it by 1dB to 0.9% should be noticeable.

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MrBrightSide
OP MrBrightSide Contributing Member • Posts: 748
Subjectivity Is The Doorway Back To The Dark Ages

D Cox wrote:

Monitor settings and ambient light will affect how visible the noise is.

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.

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

MrBrightSide
OP MrBrightSide Contributing Member • Posts: 748
Re: How Do I Measure Noise Using Photoshop? And What Is A Significant Change?

Indeed, noise can be a very useful creative tool.  But unlike most people, I believe in the liberating power of hard data.

To me knowing exactly what  a camera will do when used a certain way is no different from a blacksmith knowing optimal temperatures for various metalworking operations or a painter knowing which ratio of pigment to oil will produce the type of texture he needs to create a specific effect.

Pursuing a creative life means you have to accumulate a mental inventory of thousands of facts, strategies, work-arounds, shortcuts, and parameters that you can call on when you are in the act of creation. If you get caught up in the "subjectivity=good/objectivity=bad" paradigm you'll waste your life trying to reinvent wheels that were perfected long ago

ken_in_nh wrote:

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

I think you may be thinking of the long gone scientific version of Photoshop, which had a generous set of measurement tools built in, but none for formal noise measurement IIRC.

Failing that, what other simple methods are there to measure noise in digital photos.

No simple way to measure noise. In electronic circuits, noise is typically measured (if it's measured at all these days) using standardized signals - usually from a tone generator which generates a pure sine or pure square wave, although with the latter, you don't measure true noise, but ringing and such instead.

In photography, you'd measure noise with a very uniform grey scale, and measure it at different light intensities. But why?

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

You're thinking about it the wrong way. Outside scientific imaging, and go to Edmund's Optics (https://www.edmundoptics.com/ ) if you want to learn more about that, photography is largely perceptual, artistic if you will. This means that one's reaction to noise in an image is both highly subjective, and variable depending on the scene and artistic intent. That's why grain, a kind of noise, is a plus in some images.

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Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 14,350
The Dark Ages got some things right

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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MrBrightSide
OP MrBrightSide Contributing Member • Posts: 748
Science To The Rescue Again

You are a lifesaver. I shoot in problematic light quite a bit and the hard part for me is  figuring out whether I'm making intelligent tradeoffs in shutter/aperture/light temp/ISO/gear. Being able to shoot a ColorChecker and compare the deviation between squares will go a long way to answering the questions I run into.

Then the question turns back to how many standard deviations is significant? Seems like we humans use 1 as the yardstick and that will do until experience proves otherwise.

knickerhawk wrote:

MrBrightSide wrote:

Question 1: Long ago I remember reading that you could use the statistics tools in Photoshop to measure the noise in a photograph. There must be something in the program because it has noise reduction so it must be able to identify noise. How does it work?

There is no direct, objective/statistical measurement of noise in PS. However, there is an indirect objective measurement that provides some useful insight into noise. You can use the standard deviation measurement that appears in the histogram tool to compare uniform patches that don't have any detail. A good example is the gray patches in the GretagMacbeth chart in the DPR studio scene. Since we know that those patches are highly uniform with no intended detail, deviations in a spatial measurement of the patches is highly indicative of noise. Thus, a higher standard deviation score for the same patch under same exposure conditions is objectively measurable evidence of the difference in the amount of noise. For example:

The Std Dev for the selected region of the ISO 400 shot is 4.42 here. Note the steep relatively "thin" and lined up peaks in the histogram itself.

With the selection moved down to the ISO 3200 patch, the Std Dev score is significantly higher (12.67) and the shapes of the humps in the histograms are also spread out. Thus, we have an objective score and an objective visual representation of the difference in noise between the two patches.

While the Standard Deviation measurement in PS is useful, it should be used with caution, especially when comparing areas that are not known to be identical. Also, other image factors (such as detail and color) can be confounding, and even minor and difficult to detect differences in processing can significantly affect the usefulness of the standard deviation score as an objective noise measurement.

Failing that, what other simple methods are there to measure noise in digital photos.

Question 2: Once the noise is measure what constitutes a significant difference in the noise level? Does it fall at 1 percent noisier? 10 percent? 100 percent?

Question 3: There is no question 3. This is a reminder that no one has the patience for your thoughts about subjectivity and how everyone has a different pain threshold when it comes to noise.

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MrBrightSide
OP MrBrightSide Contributing Member • Posts: 748
Re: The Dark Ages got some things right

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.

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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photonut2008 Veteran Member • Posts: 4,962
Re: The Dark Ages got some things right

MrBrightSide wrote:

To get through this world with your sanity and soul intact all you really need are two things: an intro to stats textbook

"There are three kinds of lies: lies, damned lies, and statistics." -- (likely) Mark Twain.

and the Bible.

I've seen a lot of debates where both sides quoted The Bible extensively.

Oh, and a camera.

There is no "truth" here either, but I do endorse photography as a means for attaining greater sanity and as a soulful activity.

drj3 Veteran Member • Posts: 9,438
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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drj3

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