Lossless rotation in Irfanview

Discussion in 'Digital Photography' started by Terry Orchard, Nov 11, 2003.

  1. Irfanview has a lossless rotation option that lets you rotate a jpg
    image 90 or 180 degrees, without recompressing the data. On the
    lossless rotation dialog, there is a checkbox for "Optimize Jpg File".
    Does anyone know what that does?

    I ran a test on a file, that was originally 907,010 bytes in size.
    When I did a lossless rotation with this checkbox un-checked, the
    result was 906,430 bytes. When I did a lossless rotation with this
    checkbox checked, the result was 895,116 bytes.

    When I opened the two files and saved them as bmp's, and compared
    them, they were identical, so the "optimize" is not converting
    lossless to lossy. And they both appear to have preserved the EXIF

    Any clues? TIA,

    Terry Orchard, Nov 11, 2003
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  2. Terry Orchard

    Mike S. Guest

    The code is derived from JPEGTRAN, a utility from the JPEG Group which
    offers an "-optimize" option in the command list. From the original
    description I think it optimizes the structure of the Huffman tables to
    provide more efficient coding and smaller file size. The actual content of
    the bitmap image is not changed.

    From the docs:

    Perform optimization of entropy encoding parameters. Without
    this, default encoding parameters are used. -optimize usually
    makes the JPEG file a little smaller, but at the price of
    slower compression. Note that -progressive implies -optimize.
    Mike S., Nov 11, 2003
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  3. Thanks!
    Terry Orchard, Nov 11, 2003
  4. See also http://jpegclub.org/jpegcrop/

    Guido Vollbeding, Nov 12, 2003
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