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    Adjust channel offset


    Trying to adjust badly scanned images where it appears there is a misaligned color channels. Found FF channel offset filter which could apparently adjust channels separately but makes it worse.
    The offset step is too big, just changing slider by one step it moves by 3 pixels not one. Any alternatives?



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    #2
    You can do this in Photoshop. Get CS2 for free. Open the channels palette, select one channel, click the eyes to show the other channels too, select the move tool, and use the arrow keys to nudge a channel.

    But it doesn't look like there is a consistent offset on this image. Some lines have purple on the left, while others have green on the left and purple on the right.

    Scanners will always have a slight color fringe because the sensor pixels are arranged side by side and sample slightly different positions. Thin CIS suffer more from this.

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      #3
      I have done this in Photoshop it was some auto-align channels or something like that. But it makes colors lighter in other part of the image.
      Why the offset is not consistent and could it be software "recalibrated"?

      This is using Photoshop. I will post later part of scanned map to show the issue with colors.
      Click image for larger version

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        #4
        This filter. Is there such in CS2? Also looking for alternative to use in Irfanview and to not lose color vibrance.
        Click image for larger version

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ID:	93845Click image for larger version

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        Attached Files

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          #5
          Does your scanner have a calibration function?
          My system: IrfanView 4.62 64bit, Windows 10 22H2, Intel Core i5-3570, 16GB RAM, NVidia GTX 1050Ti 4GB

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            #6
            Even if it has it doesn't matter these scans are available as opendata from National Library. It seems maps were scanned by blind bats.

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              #7
              "Reduce noise" does give me a similar result to yours in Photoshop CS2. It separates the image into brightness and color, and heavily lowpasses the color, similar to JPEG subsampling. So, you have to sacrifice color resolution. A manual method with a similar result is to blur a duplicate layer and recombine it with the source using the blending mode Color, but that loses more resolution. Maybe searching for "chromatic aberration" can turn up other useful methods. If you make a simple linear shift to a color channel to correct one part of this image, other parts look worse.

              Scanning at the highest resolution and downsampling could produce a cleaner image.

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                #8
                Use Photoshop

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