Name

---

      GMASCL

Purpose

---

      This is a utility routine to perform basic gray-level pixel
      transformations of images. I think of it as BYTSCL on steroids.
      It is similar to IMADJUST in _Digital Image Processing with MATLAB_
      by Gonzales, Wood, and Eddins. It performs a log scaling of the
      image array.

Author

---

      FANNING SOFTWARE CONSULTING
      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

Category

---

      Utilities

Calling Sequence

---

      scaledImage = GMASCL(image)

Arguments

---

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

Keywords

---

      GAMMA: The exponent in a power-law transformation (image^gamma). A gamma
                      value of 1 results in a linear distribution of values between
                      OMIN and OMAX. Gamma values less than 1 map darker image values
                      into a wider range of output values, and Gamma values
                      greater than 1 maps lighter image values into a wider
                      range of output values. The gamma value is constrained to
                      be greater than 1.0e-6.
      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.
      NEGATIVE: If set, the "negative" of the result is returned.
      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

---

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

Common Blocks

---

      None.

Examples

---

      LoadCT, 0 ; Gray-scale colors.
      image = cgDemoData(11) ; Load image.
      TV, GmaScl(image, Min=30, Max=100) ; Similar to BytScl.
      TV, GmaScl(image, /Negative) ; Produce negative image.
      power = Shift(ALog(Abs(FFT(image,-1))), 124, 124) ; Create power spectrum.
      TV, GmaScl(power, Gamma=2.5) ; View power specturm with gamma correction.
      TV, GmaScl(power, Gamma=2.5, /Negative) ; Reverse power spectrum.

Restrictions

---

    Requires SCALE_VECTOR from the Coyote Library:
        http://www.idlcoyote.com/programs/scale_vector.pro

Modification History

---

      Written by: David W. Fanning, 17 February 2006.
      Fixed a problem with output scaling. 1 July 2009. DWF (with input from Bo Milvang-Jensen).
      Now setting NAN keyword on all MIN and MAX functions. 2 Dec 2011. DWF.