How to deactivate auto denoise/sharpen in Preview?

Question

Level 1

4 points

How to deactivate auto denoise/sharpen in Preview?

Hi,

"Quick preview" (pressing space bar on .jpeg file) does display the picture properly (including the true grain contain in the picture).

BUT opening it in preview automatically apply some kind of denoise/sharpen which remove that grain, resulting in not displaying the picture correctly. (as it denoise is a modification and it doesn't ask me before doing it).

Where could I deactivate that sharpen/denoise function? I do not find any settings about it.

I am working with Fujifilm pictures that do contain grain and I am expecting Preview to display this correctly without applying changes.

Easy to reproduce, open any picture containing grain/noise and see the diff in between quick preview and open in preview. For jpeg > 20MB I can even "see" the denoise process happening (take 1s but still visible)

Thanks.

Regards,

[macbook pro 14 2021, M1 Pro, Ventura 13.3.1]

MacBook Pro 14″, macOS 13.3

Posted on Apr 24, 2023 7:36 AM

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Answer 1

auzadrien Author

Level 1

4 points

Apr 25, 2023 1:33 AM in response to auzadrien

OK - I've found a workaround.

So in Preview it's clearly a zoom related issue. Something "smooth" the image while scaling it down. I can't find any documentation on this "feature". The com.apple.Preview settings aren't all clear and not documented either. I've tried changing PVImageRespectDPIForScaleMode to 1 but that doesn't fix the issue. Same with disabling the "smooth picture" options in the Accessibility settings.Strange that quickpreview doesn't do the same. (nor the tiny picture when looking at the FileInfo in Finder)

Qview has the same issue BUT it has two settings we can deactivate that fix this and allow to display the image properly. Must deactivate " Bilinear Filtering " and " Image Scaling " That'll be my workaround for now.

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Answer 2

léonie

Level 10

200,735 points

Apr 25, 2023 1:46 AM in response to auzadrien

auzadrien wrote:

...

So in Preview it's clearly a zoom related issue. Something "smooth" the image while scaling it down. I can't find any documentation on this "feature".

...

When an image is scaled down, Photos has to subsample the image, and it is state of the art to apply a low pass filter before sampling the image. Otherwise the scaled image will be showing horrible aliasing artifacts and would be useless (in violation of the Sampling Theorem ). The anti aliasing will suppress high frequencies and this would explain the noise reduction you are seeing.

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Answer 3

dialabrain

Level 10

136,379 points

Apr 24, 2023 7:45 AM in response to auzadrien

I don't believe there is such process in Preview. First try changing Preview > Settings > Images > Define 100% scale as:

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Answer 4

Apr 24, 2023 8:08 AM in response to auzadrien

To me it just looks like the quick preview is showing a lower resolution which looks pixelated. When opening in the Preview app, it is showing the full resolution which looks like smoothing, but it is just not pixellated like the lower quality version.

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Answer 5

dialabrain

Level 10

136,379 points

Apr 24, 2023 8:12 AM in response to Mac Jim ID

Mac Jim ID wrote:

To me it just looks like the quick preview is showing a lower resolution which looks pixelated. When opening in the Preview app, it is showing the full resolution which looks like smoothing, but it is just not pixellated like the lower quality version.

Do you see a difference in the screen shot I posted?

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Answer 6

Apr 24, 2023 8:24 AM in response to dialabrain

Not in the pic you posted, but definitely in the one from the original poster. Depending on the size of the original image, the quick preview will show a lower resolution version to fit in the smaller window size of the quick preview.

I have the same scale settings as you do in Preview, but this does not affect the size of the image when hitting the space bar to do a quick preview. If the original will fit in the quick preview, than no scaling is done, but if larger than scaling will be done to fit in the window completely.

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Answer 7

dialabrain

Level 10

136,379 points

Apr 24, 2023 8:30 AM in response to Mac Jim ID

Mac Jim ID wrote:

Not in the pic you posted, but definitely in the one from the original poster. Depending on the size of the original image, the quick preview will show a lower resolution version to fit in the smaller window size of the quick preview.

FWIW, the images the user posted are not pixelated. The shot on the right has grain as mine does. His Preview image is smoothed out for some reason.

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Answer 8

dialabrain

Level 10

136,379 points

Apr 24, 2023 8:30 AM in response to auzadrien

auzadrien wrote:

OF COURSE if the picture has no grain you won't see any difference. which also exclude a difference of "resolution" in between preview and quick preview.

The picture I posted has all kinds of grain.

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Answer 9

auzadrien Author

Level 1

4 points

Apr 24, 2023 9:01 AM in response to dialabrain

that "smoothed out for some reason" is what I've called auto denoise/sharpen and would like to find a way to deactivate. How do I start preview in debug mode with verbose logs to see every process/calls it's making?

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Answer 10

dialabrain

Level 10

136,379 points

Apr 24, 2023 9:08 AM in response to auzadrien

auzadrien wrote:

that "smoothed out for some reason" is what I've called auto denoise/sharpen and would like to find a way to deactivate. How do I start preview in debug mode with verbose logs to see every process/calls it's making?

Yes, I understood your post and as I said, I don't believe Preview has some built-in process. It certainly doesn't on my Macs and I have seven of them. In any case, I can't tell you how to launch Preview in debug mode.

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