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Thread: Decrease color depth - Save file

  1. #1
    IV Newbie
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    Default Decrease color depth - Save file

    Hy!
    I decreased a png color depth to 256 (8bit), because the number of unique colors was 164. The size of the file was reduced by 75%, so everything looks good:
    Click image for larger version. 

Name:	02-13-IrfanView.png 
Views:	8 
Size:	40.8 KB 
ID:	5508

    now I save it but new file jump back to 24 BPP so file size don't changed?

    What's wrong, please help!

  2. #2
    Professional User Mij's Avatar
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    There is no reason why the file you show the information for should not save at a 256(8 bit) color depth. There are some Irfanview features that only work at 24bit color depth though. If you apply one of them before saving then your file will revert to 24 bit. The most common one that catches people out is the Resize/Resample function but there are others. Keep an eye on the information on the status bar below the image and make sure that you have not changed it back to 24 bit before you save. If possible make the decrease color depth function the last thing you do before saving.

  3. #3
    Power User j7n's Avatar
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    Check the Save Options for PNG. You might have enabled Save Transparency as Alpha Channel which will upconvert the image to truecolor, or you may have selected a RGB color type for PNGOUT. I see that the original colors for this image is 32 BitsPerPixel, which means that it has an alpha channel.

  4. #4
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    Quote Originally Posted by j7n View Post
    Check the Save Options for PNG. You might have enabled Save Transparency as Alpha Channel which will upconvert the image to truecolor.
    solved, thank You!

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