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    Gamma correction won't take

    I have a B/W CAD type drawing in TIFF format that I am trying to adjust because the lines and text are not dark enough to print clearly. I use the Enhance Colors adjustment and tweek the Gamma to get a nice picture when I press the Adjust Original Image button. When I press OK, the image goes back to it's original look, just as if no adjustment has been made.

    WTF?

    Rick

    #2
    If it is B/W - that is, truly 1 bit per pixel two-color black and white, no adjustment is possible. If you increase the color depth first, you should be able to adjust gamma.
    Its: Belongs to "It"
    It's: Shortened form of "It is"
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    Lose: Fail to keep
    Loose: Not tight

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    Plurals do not require apostrophes

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      #3
      Hi Rick,

      If your image is "truly 1 bit per pixel two-color black and white" as matera understood, no need to increase the contrast: it is already maximum. So I supposed you was meaning greyscale image and I tried on a (256) greayscale image but I couldn't reproduce what you described.

      Laurent
      Before you post ... fill in your OS and IV version in your profile.

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        #4
        I increased the color depth from 4 BPP to 8BPP, tried the same adjustment of gamma and had the same thing happen. The image shows a change when I do "apply to original", but the changes disappear when I then press OK (doing Enhance Colors). I tried a simple brightness and contrast adjustment with the same result. I then converted the image to greyscale -- still didn't work. I'm running out of ideas.

        Rick

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          #5
          There are a number of different "sub-formats" in tiff. You might have to re-save it (with the options dialog on). Then raise the color depth and try again.

          I tried a couple of variations and the results were interesting. Some compression formats revert and some don't. Better take notes (and back up the original!)
          Its: Belongs to "It"
          It's: Shortened form of "It is"
          ---------------------
          Lose: Fail to keep
          Loose: Not tight

          ---------------------
          Plurals do not require apostrophes

          Comment


            #6
            I tried doing the same adjustments after converting the file to BMP format (4 BPP) -- same results. It's strange that I can convert the file in Irfanview to any format (destructive editing), but can't do any image enhancements (non-destructive). Is there some "switch" in the program that could be causing the problem? I can't find any obvious control that would cause this behavior.

            Rick

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              #7
              I wouldn't call all image enhancements "non-destructive," not after some of the wild experiments I've done...but anyway... By "same results" you mean that you couldn't adjust the 4bpp BMP? Ack, that is strange. I don't know of any switch that could affect it that way. I have no problem adjusting anything with more than two colors. I'm beginning to wonder if it could be some mysterious system screwup completely outside of I-V.
              Its: Belongs to "It"
              It's: Shortened form of "It is"
              ---------------------
              Lose: Fail to keep
              Loose: Not tight

              ---------------------
              Plurals do not require apostrophes

              Comment


                #8
                I took the file to my home computer to see if it was a system problem, and had similar bad results. But because my home system is an order of magnitude better than the dinosaur I have at work, I was able to try of bunch of other things without having to wait forever for the computer to respond. I finally came up with a method for pulling the text and lines from the drawing out to the point where they would be readable when printed. I ran the original B/W (4 BPP actually) file through he edge detection filter, then took the negative image of that. This gave me a fairly decent result and a 24 BPP image. I could then do some fine adjustment of brightness, contrast and gamma and have the results "take". Oh, I also decimated (resampled) the file from its original 13200 x 10200 pixels down to 1600 x 1200. This provided much quicker computer response at work, and significantly decreased the file size.

                Thanks for your help matera. The problem with the adjustments not taking seemed to be related to the image size. Once I resampled the image, I was able to do all the adjustments without a problem.

                Rick

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