5 Replies Latest reply: Jul 16, 2014 11:19 AM by avpromedia RSS

    Gaussian blur results in banding

    avpromedia Community Member

      Here's a piece of wall I try to gaussian blur (> 60 radius) and always results in bandings. I tried adding noise but it doesn't help, unless I add so much noise the image becomes unrecognizable.

       

      gray.png

      Here's the same image in case the one above is re-compressed

      blur

       

      In case you wonder why blur this image, there is an electrical outlet near this wall (not shown) that I edited out and need to blur the edited area, and realize the resulting banding is caused by the wall and photoshop.

       

      Are there other solutions?

       

      I'm using photoshop CS4 in 16 bit mode.

        • 1. Re: Gaussian blur results in banding
          Noel Carboni Community Member

          You may be using Photoshop in 16 bits/channel mode, but you're displaying the image on your monitor in 8 bits/channel mode (x 3 channels = 24 bit color).  Additionally, even though the PNG you saved is in 16 bits/channel mode, our browsers are displaying it on our monitors in 8 bits as well.

           

          You're just seeing the limitations of the display medium.  The question is, what medium do you need to prepare this image for?  Print?

           

          You can prove this by radically enhancing the image with extreme curves operations, which, if the banding really was in the image would be made obvious.  But it stays smooth.

           

          It's also possible your monitor is not set up optimally, and you're getting adjacent 2 luminance level jumps.  On the best 24 bit color setups every level is discretely displayed and banding is all but invisible.  What is your hardware and calibration setup?

           

          -Noel

          • 2. Re: Gaussian blur results in banding
            Noel Carboni Community Member

            Further, note that with exactly the right combination of hardware, software, and magic incantations it's sometimes possible to get Photoshop to display things in 30 bit color (10 bits/channel), which is precisely to deal with cases where images need to be viewed with such accuracy that 24 bit color isn't quite good enough.

             

            I haven't personally achieved 30 bit operation, but I know some who have.

             

            -Noel

            • 3. Re: Gaussian blur results in banding
              avpromedia Community Member

              I need to display it on a web album or web page without the banding showing.

              The photo in the post is the pre-blur photo. If you copy that into photoshop and blur it yourself you will see the banding.

              The photos in the link contain both a pre-blur and a post-blur photo.

               

              It doesn't matter to me where the limitation is, I want the banding not visible after I perform blur.

              Is higher precision arithmatic the only answer?

              • 4. Re: Gaussian blur results in banding
                Noel Carboni Community Member

                Yes, I know what you're talking about.  It's as though you don't want to accept the explanation.

                 

                With 24 bit color you will see the divisions between regions of identical RGB values in the 24 bit color space where they change by one level.  It's most easily seen in gray or near gray gradients of dim luminosity (which is what you have here).

                 

                There is no uneven banding in the data in the image you posted.  It's a 16 bit PNG file and the data is perfectly clean and smooth, which is what you'd expect from a large radius Gaussian Blur.

                 

                If you're seeing uneven or more severe banding on your display only, it's possible something in your system setup is amiss (e.g. a poorly constructed monitor profile, or a malfunctioning display driver), causing you to see multi-level jumps between adjacent regions of color.

                 

                On my very well tuned 24 bit color setup I can see the even (but very subtle) banding of your 16 bit image.  Doing the following hides it completely:

                 

                NoMoreBanding.png

                 

                If your display setup is functioning optimally you won't sense any banding in the above image (after having clicked it to make it show at full size of course).

                 

                -Noel

                • 5. Re: Gaussian blur results in banding
                  avpromedia Community Member

                  You're very right!

                  I displayed the image with banding on an ipad and the banding looks less visible. I also did the curve adjustment and the banding did not become any more obvious.

                  I must have been asleep when I read your reply.

                   

                  I tried it on a more expensive monitor (dell U3011) and the banding is less obvious, but still couldn't get rid of them after adding noise before blurring.

                   

                  Both monitors (with banding displayed) have been calibrated with color eyes display pro. It didn't report banding issues; maybe it doesn't detect it.

                  I don't suppose there is a fix for banding on monitors.