Photoshop: Dust and scratches not taking effect when clicking OK (not viewing at 100%)

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  • Updated 5 years ago
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  • (Edited)
When I adjust the dust and scratches filter settings to something quite low (e.g. radius of 1 or 2 and threshold of 26) I see the changes on my screen. But when I click OK the changes disappear as though no alteration has been made. The radius has to be at least 3 or 4 before the changes take effect when I click OK. I am using a 64 Bit PC, Windows 7 and Photoshop CS6 (not Cloud version). I don't remember this happening before.
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William Jupe

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Posted 5 years ago

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Charles Badland

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Are you viewing at 100%?
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William Jupe

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Thanks for your help, Charles. No, I wasn't viewing at 100%, but at about 30%. At 30%, which allows me to look at the whole image, the modest adjustments mentioned above tidied the picture perfectly - until I clicked OK, and then it seemed that no changes had taken place at all. After reading your post I made the same small adjustments, but viewing at 100%. This time the modest settings appeared to make only a very tiny change to the image (not nearly enough) - but clicking OK did confirm these small changes.

So it seems that Dust and Scratches DOES work. It just doesn't preview effectively at less than 100%. Which is frustrating and unhelpful when I need to see how the changes will effect the whole image.

The thing is, I don't remember having this problem before, and I use Dust and Scratches a lot.
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Charles Badland

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Some images display at lower percent views display better than others. But anytime you view less than 100%, you will have more than one image pixel represented by just one monitor pixel. Because of this interpolation, less than Actual Pixels view can not be used to accurately see what editing is taking place. Especially when it comes to small, high contrast detail, as you can have with Dust and Scratches.
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William Jupe

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Thanks again, Charles. It does make sense - that, 'anytime you view less than 100%, you will have more than one image pixel represented by just one monitor pixel'. But why is it, do you think, that the monitor shows such a different representation of my image in Dust and Scratches Preview compared with when I click OK, when both times I am viewing the image at 30%? I would have expected the monitor to struggle similarly in both situations.
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Charles Badland

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Yep. I agree. That is the question I have had for years...
It is not just D&S preview, you can see it when you flatten an image, merge layers, merge Adjustment Layers, apply some filters...

Anything less than 100% view is not accurate by its nature, but why will a 33% preview look one way, then look different when applied (or flattened, or merged, etc).
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Chris Cox

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Think about the worst case: a 2x2 pixel checkerboard. When seen at 100% it is pure black and white. When seen at 50% it is just 50% gray.
Filters or adjustments applied to that 50% gray will show an effect that looks nothing like the same filter or adjustment applied to the pure black and white image.

As long as you're looking at downsampled previews, there is a chance that you're not seeing the full effect.
And the difference is greatest when there is a lot of noise/detail in the image.
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William Jupe

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Many thanks to you both, Charles and Chris, for trying to shed some light on this. There was indeed a lot of noise/detail in the image I was working on, and that's probably why I noticed the problem particularly today.

But I still don't understand why the D&S filter effect looks different at 30% view in preview compared with when I click OK. What has changed? I'm no technical wiz, but might it be that Photoshop is designed not to expend too much processing power generating previews? If that's the case, is there (or could there be) a setting we could change? Bridge, for example, gives the option to 'generate 100% previews'...
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Charles Badland

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Exactly. That shift has always been around. Nothing new. But why the change from a preview at 33% to the 33% image after applying the adjustment or filter. I understand neither may be very accurate, but why inconsistant between the two down-sampled views.
A quick way to see this is run a default Graphic Pen filter on a 1200 x 1200 image. Zoom down to 25%. Now run a Levels Adjustment. Its preview at 25% will not match the 25% image after applying the adjustment.
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William Jupe

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I agree - it's a problem that crops up at various different times and is infuriating. I guess we'll have to stick with trial and error! Previewing, applying the changes, reviewing, undoing, then doing it all again, and again, and again... Time to create an Action.