Anyone here using imageMagick?

Discussion in 'Digital Photography' started by Mike Henley, Oct 31, 2005.

  1. Mike Henley

    Mike Henley Guest

    Mike Henley, Oct 31, 2005
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  2. Mike Henley

    Paul Allen Guest

    I use it as an image viewer, but I don't do any editing with it any
    more. My image cataloging perl script used to use it for rotation,
    cropping, resizing, and slideshows. It's cropping and rotation are
    lossy, so I switched over to jpegtran for those functions. For
    resizing I'm now using Image::Resize, which is based on the gd library.
    The slideshow mode has turned out to be not important enough to

    For serious editing, I use the GIMP. It's not Photoshop, but it's

    Paul Allen
    Paul Allen, Oct 31, 2005
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  3. Mike Henley

    a Guest

    I use the Windows version, controlled by PHP scripts to generate the
    images and thumbnails for my site.
    a, Oct 31, 2005
  4. I use it every now and then for image viewing and simple batch
    processing. For complicated batch processing, the Gimp can be used in
    batch mode, although I don't use that all too frequently.
    =?iso-8859-1?q?M=E5ns_Rullg=E5rd?=, Oct 31, 2005
  5. Mike Henley

    Bill Tuthill Guest

    ImageMagick is better than GIMP for resampling, especially downsampling.
    You get a wider choice of algorithms and some seem to be better implemented.

    I like the "identify" program to check out file type.

    The "composite -compose difference" command is easier than trying to tell
    the difference between two images using the Photoshop difference layer.

    ImageMagick and GIMP are better than Photoshop for editing and writing JPEG.

    Maybe I could think of some more uses for ImageMagick. It's well worth
    compiling and installing if you have any interest in imaging.
    Bill Tuthill, Oct 31, 2005
  6. Mike Henley

    a Guest

    Why doesn't Photoshop offer the Lanczos downsampling filter ?
    a, Oct 31, 2005
  7. SNIP
    Yes, down-sampling is implemented as it should, with proper

    This is an example of how it works out on a real life image (a
    filmscan, so the graininess masks some of the issues that show with a

    Bart van der Wolf, Nov 1, 2005
  8. Mike Henley

    Bill Tuthill Guest

    I think you forgot to give this URL:

    Thanks for all your pioneering research in this important area, Bart.
    Thumbnail quality is absolutely critical for my website, and you have
    helped me make progress in that area.
    Bill Tuthill, Nov 1, 2005
  9. Mike Henley

    Iraxl Enb Guest

    I use ImageMagick-based executable and a script to
    generate web albums of my photos. The images are
    resized using the ImageMagick libraries, and then the
    web pages are generated...

    More info and download at

    Feel free to make changes, and if you want to pass on
    any ideas/changes, let me know...

    Iraxl Enb, Nov 1, 2005
  10. OOPS, you're right. Thanks for the correction.
    Thank you for the kind words. It has always struck me as odd that
    usually more emphasis is given to image magnification, when the vast
    and increasing majority of images needs to be down-sampled. It was the
    lack of available references that forced me to explore the topic
    myself. Sharing my findings was a minor step.

    Bart van der Wolf, Nov 2, 2005
  11. It is one seriously powerful toolset. The "convert" command can do
    some awesome stuff. Check

    original.jpg is a worst-case scenario. Part of the picture properly
    exposed, part grossly underexposed. Chapter01 is a sub-gallery with
    samples of how much I could salvage out of that picture. For a normal
    picture that is slightly underexposed, ImageMagick will straighten it
    out easily. I plan to show more examples later. I'm currently working
    on writing custom maps for even better control. The formulas that work
    best so far for boosting partially underexposed photos are...

    1) Power curve
    convert original_image -fx 'u^power' output_image
    where "power" is a number between 0 and 1. e.g....

    convert original.jpg -fx 'u^0.3' output.jpg

    The lower the value of "power" (i.e. closer to zero), the more boost you
    get in underexposed areas.

    2) Logarithmic curve
    convert original_image -fx 'ln(u*(number-1)+1)/ln(number)' output_image
    where "number" is a positive number greater than 1, e.g....
    convert original.jpg -fx ' -fx 'ln(u*(255)+1)/ln(256)' output.jpg

    The higher the value of "number", the more boost you get in underexposed

    Some notes...

    - It takes some trial and error to figure out the best coefficients.
    For more boost, use a lower "power" or higher "number".

    - The "convert" command defaults to creating tiff files with 16-bit
    colour channels. You have to explicitly tell it if you want 8-bit
    colour channels. The above examples, outputting to tiff, would have
    looked like so...
    convert -depth 8 original.tif -fx 'u^0.3' output.tif
    convert -depth 8 original.tif -fx 'ln(u*(255)+1)/ln(256)' output.tif

    - You can mix and match image file types, e.g. jpeg to tiff or visa
    versa. "convert" recognizes file extensions.
    Walter Dnes (delete the 'z' to get my real address, Nov 5, 2005
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