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    Image Properties, Resolution

    I notice that on the Resize dialogue (Control R), there is an option to change the DPI for the image. However, on the Image Information dialogue there are separate options for horizontal and vertical resolution.

    Can anyone tell me why one would need different horizontal and vertical resolutions in an image? Wouldn't it be better if this dialogue had a single field for DPI instead of two? It just makes unnecessary work, and increases the likelihood of errors.
    Before you post ... Edit your profile • IrfanView 4.62 • Windows 10 Home 19045.2486

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    #2
    Originally posted by Bhikkhu Pesala View Post
    Can anyone tell me why one would need different horizontal and vertical resolutions in an image?
    I suppose that there are two separated fields because the DIB specification (in particular, the BITMAPINFOHEADER structure) use two separated fields. This may be useful for some strange devices that have different horizontal and vertical resolutions: in the old times of the first versions of Windows - when the DIB standard was defined - many screen modes had a different vertical/horizontal DPI (the pixels on the screen actually were rectangular), and many printers too have different V/H resolution. Thus the different V/H resolution settings are actually useless for the user, but are sometimes used in the applications.
    IrfanPaint developer
    The latest stable IrfanPaint version is the 0.4.13.70.
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      #3
      Originally posted by Bhikkhu Pesala View Post
      Can anyone tell me why one would need different horizontal and vertical resolutions in an image? Wouldn't it be better if this dialogue had a single field for DPI instead of two? It just makes unnecessary work, and increases the likelihood of errors.
      Not all images define squared pixels. Especially images from fax machines.
      If you are opening a tiff encoded with G3 FAX (which quiet often uses different dpi values for rows and columns) then Irfanview will scale the image for you so that the image will look correct on a screen using squared pixels.

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        #4
        Thanks all. It looks like the option is necessary then.
        Before you post ... Edit your profile • IrfanView 4.62 • Windows 10 Home 19045.2486

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          #5
          Hi guys

          How do I make a picture smaller and not lose the quality - pixels?
          builders

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            #6
            You cannot, unless you just mean making it smaller on the page when placed in DTP applications, in which increasing the DPI will do that. Less pixels means less information, which inevitably means lower quality. Resampling will give a decent result as long as you dont reduce the detail (pixel count) too much.
            Before you post ... Edit your profile • IrfanView 4.62 • Windows 10 Home 19045.2486

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