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Grayscale image is designated as color by the Paint tool

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    #16
    I can confirm, that sometimes 8bit grayscale images are converted to 24bit grayscale. But I don't think it's IrfanPaint, but Irfanview itself.
    Since it doesn't bother me much I never tried to find the reason for this behaviour. I don't consider this a bug, but a feature or technically necessary.
    Ineuw, you might want to ask the developer for the reason. Goto 'Help > About IrfanView' for his mail address and let us know his answer.
    Win 10/64 Home 22H2 IrfanView 4.66/64
    Hate has caused a lot of problems in this world, but it has not solved one yet. (Maya Angelou)

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      #17
      Originally posted by Kuki Dent View Post
      I can confirm, that sometimes 8bit grayscale images are converted to 24bit grayscale. But I don't think it's IrfanPaint, but Irfanview itself.
      That's true. Some features of IrfanView work only in truecolor (24 bits), so the picture is converted automatically when some of those features is used. These are mostly various filters.

      Grayscale pictures are internally handled as pictures with 256 color palette. You can view the palette, it consists of 256 shades of gray. However IrfanView will detect, if the palette contains only shades of gray, and will treat the picture accordingly.
      Last edited by JendaLinda; 15.10.2020, 06:10 PM.
      My system: IrfanView 4.62 64bit, Windows 10 22H2, Intel Core i5-3570, 16GB RAM, NVidia GTX 1050Ti 4GB

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        #18
        Originally posted by JendaLinda View Post
        That's true. Some features of IrfanView work only in truecolor (24 bits), so the picture is converted automatically when some of those features is used. These are mostly various filters.

        Grayscale pictures are internally handled as pictures with 256 color palette. You can view the palette, it consists of 256 shades of gray. However IrfanView will detect, if the palette contains only shades of gray, and will treat the picture accordingly.
        I also thought that it's caused by my Option selections, but wouldn't know where to look. Aside from that, I still think that when Grayscale is selected, the color depth and dithering be disabled.

        I took screenshots of the change and will post them at https://imagesharing.com/uploads/202...b6cc926b53.jpg and https://imagesharing.com/uploads/202...aced36c763.jpg
        Irfanview 4.54, Win 10 Pro 64bit 16gb RAM, Intel UHD graphics

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          #19
          Originally posted by ineuw View Post
          The picture was saved as 24 bpp (truecolor) before, see the "original colors".

          Could you post your batch conversion settings?
          My system: IrfanView 4.62 64bit, Windows 10 22H2, Intel Core i5-3570, 16GB RAM, NVidia GTX 1050Ti 4GB

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            #20
            Attached is the requested batch advanced options page.

            I also have questions about the .jpg options appearing when saving. You'll notice that I switched from .png back to .jpg. The issue of colour exists with both formats, and colour loss is of no importance. But makes a difference when uploading ~900 images.
            Attached Files
            Irfanview 4.54, Win 10 Pro 64bit 16gb RAM, Intel UHD graphics

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              #21
              This looks correct. This setting should produce 8bpp grayscale images.

              In any case, I recommend to use a different format for editing. I would use PNG or BMP. Saving a picture in JPEG multiple times may degrade the picture quality. I recommend to use JPEG as the last step before upload.

              JPEG is quite special and doesn't internally use 24 bpp or 8 bpp encoding. However in the JPEG options, you may enable the grayscale mode too. This will force all JPEGs to be saved in grayscale.
              My system: IrfanView 4.62 64bit, Windows 10 22H2, Intel Core i5-3570, 16GB RAM, NVidia GTX 1050Ti 4GB

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                #22
                Originally posted by JendaLinda View Post
                This looks correct. This setting should produce 8bpp grayscale images.

                In any case, I recommend to use a different format for editing. I would use PNG or BMP. Saving a picture in JPEG multiple times may degrade the picture quality. I recommend to use JPEG as the last step before upload.

                JPEG is quite special and doesn't internally use 24 bpp or 8 bpp encoding. However in the JPEG options, you may enable the grayscale mode too. This will force all JPEGs to be saved in grayscale.
                You are absolutely right!! And thanks for your patience. .jpg is uncontrollable. Even though I set both the load as and save as grayscale, it still gave me the 16mill palette. Therefore, the reliable solution is .jp2 -> .png and upload it as such. So, I close this issue and thanks again.
                Irfanview 4.54, Win 10 Pro 64bit 16gb RAM, Intel UHD graphics

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