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      This is a utility routine to perform a log intensity transformation
      on an image. For exponent values greater than 1.0, the upper and
      lower values of the image are compressed and centered on the mean.
      Larger exponent values provide steeper compression. For exponent values
      less than 1.0, the compression is similar to gamma compression. (See
      IMGSCL.) See pages 68-70 in _Digital Image Processing with MATLAB_
      by Gonzales, Wood, and Eddins. The function is used to improve contrast
      in images.


      David Fanning, Ph.D.
      1645 Sheely Drive
      Fort Collins, CO 80526 USA
      Phone: 970-221-0438
      E-mail: david@idlcoyote.com
      Coyote's Guide to IDL Programming: http://www.idlcoyote.com



Calling Sequence

      outputImage = LOGSCL(image)


      image: The image to be scaled. Written for 2D images, but arrays
                      of any size are treated alike.


      EXPONENT: The exponent in a log transformation. By default, 4.0.
      MEAN: Values on either side of the mean will be compressed by the log.
                      The value is a normalized value between 0.0 and 1.0. By default, 0.5.
      NEGATIVE: If set, the "negative" of the result is returned.
      MAX: Any value in the input image greater than this value is
                      set to this value before scaling.
      MIN: Any value in the input image less than this value is
                      set to this value before scaling.
      OMAX: The output image is scaled between OMIN and OMAX. The
                      default value is 255.
      OMIN: The output image is scaled between OMIN and OMAX. The
                      default value is 0.

Return Value

      outputImage: The output, scaled into the range OMIN to OMAX. A byte array.

Common Blocks



      cgLoadCT, 0 ; Gray-scale colors.
      image = cgDemoData(22) ; Load image.
      cgImage, image ; No contrast.
      cgImage, LogScl(image) ; Improved contrast.
      cgImage, LogScl(image, Exponent=10, Mean=0.65) ; Even more contrast.
      cgImage, LogScl(image, /Negative, Exponent=5) ; A negative image.


    Requires cgScaleVector from the Coyote Library:

Modification History

      Written by: David W. Fanning, 20 February 2006.
      Fixed a problem with output scaling. 1 July 2009. DWF (with input from Bo Milvang-Jensen).

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