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Hjorthmedh
Known Participant
November 16, 2023
Question

Banding when doing gaussian blur (or iris blur) in 16-bit black and white mode

  • November 16, 2023
  • 13 replies
  • 2103 views

Hej! 

 

I use the new Photoshop 25.1.0 and have a problem with gaussian blur and iris blur (it might also apply to other types of blur). I see the effect for example when editing 16-bit black and white images, and applying a blur with high amounts (say 100 pixels or 200 pixels). The blurred image has banding, the grey tones are not smooth as expected. If I instead switch to RGB 16-bit, I do not see the effect on a similar image.

 

It should be pretty easy to reproduce, take a black and white 16-bit image (in my case it had a bit of noise), add gaussian blur with 200ish in radius. You should be able to see the banding in the preview. Turn off the preview, banding is gone, turn it back on banding again. Switch to 16-bit colour, apply the blur, no banding.

 

I edit a lot of black and white images, so this is a big issue.

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    13 replies

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    D Fosse
    Community Expert
    D FosseCommunity Expert
    Community Expert
    November 16, 2023

    With 16 bit data, any banding you see is in your display system.

     

    Most monitors are 8 bit, some even 6 bit + temporal dithering. That means 256 discrete steps, and gamma encoding means that these steps will be further apart in the shadows. There is nothing you can do about that.

     

    The only way to avoid it is to use a (expensive) 10 bit capable display. To not see it, add a tiny bit of noise to break it up.

     

    Banding is cumulative. It will be exaggerated by calibration tables loaded from the video card (as opposed to in the monitor's own native processor) or a bad monitor profile.

      H
      HjorthmedhAuthor
      Known Participant
      November 16, 2023

      Hej Jeff, thanks for the quick reply. Yes the "precise previews for 16-bit document" is checked. The issue also persists if I apply the blur effect to the image and view it outside of preview mode.

        Jeff Arola
        Community Expert
        Jeff ArolaCommunity Expert
        Community Expert
        November 16, 2023

        In the Adobe Photoshop 2024>Settings (Preferences)>Technology Previews do you have Precise previews for 16- bit documents checked?

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