;+
; 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: davidf@dfanning.com
;       Coyote's Guide to IDL Programming: http://www.dfanning.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 = LoadData(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.dfanning.com/programs/scale_vector.pro
;
; MODIFICATION HISTORY:
;
;       Written by:  David W. Fanning, 17 February 2006.
;-
;###########################################################################
;
; LICENSE
;
; This software is OSI Certified Open Source Software.
; OSI Certified is a certification mark of the Open Source Initiative.
;
; Copyright © 2006 Fanning Software Consulting
;
; This software is provided "as-is", without any express or
; implied warranty. In no event will the authors be held liable
; for any damages arising from the use of this software.
;
; Permission is granted to anyone to use this software for any
; purpose, including commercial applications, and to alter it and
; redistribute it freely, subject to the following restrictions:
;
; 1. The origin of this software must not be misrepresented; you must
;    not claim you wrote the original software. If you use this software
;    in a product, an acknowledgment in the product documentation
;    would be appreciated, but is not required.
;
; 2. Altered source versions must be plainly marked as such, and must
;    not be misrepresented as being the original software.
;
; 3. This notice may not be removed or altered from any source distribution.
;
; For more information on Open Source Software, visit the Open Source
; web site: http://www.opensource.org.
;
;###########################################################################
FUNCTION GmaScl, image, $
   GAMMA=gamma, $
   MAX=imageMax, $
   MIN=imageMin, $
   NEGATIVE=negative, $
   OMAX=maxOut, $
   OMIN=minOut

   ; Return to caller on error.
   ;On_Error, 2
   Catch, theError
   IF theError NE 0 THEN BEGIN
      Catch, /Cancel
      void = Error_Message()
      RETURN, vector
   ENDIF

   ; Check arguments.
   IF N_Elements(image) EQ 0 THEN Message, 'Must pass IMAGE argument.'

   ; Check for underflow of values near 0. Yuck!
   curExcept = !Except
   !Except = 0
   i = Where(image GT -1e-35 AND image LT 1e-35, count)
   IF count GT 0 THEN image[i] = 0.0
   void = Check_Math()
   !Except = curExcept

   output = Double(image)

   ; Check keywords.
   IF N_Elements(imageMax) EQ 0 THEN imageMax = Max(output)
   IF N_Elements(imageMin) EQ 0 THEN imageMin = Min(output)
   IF N_Elements(maxOut) EQ 0 THEN maxOut = 255B ELSE maxout = 0 > Byte(maxOut) < 255
   IF N_Elements(minOut) EQ 0 THEN minOut = 0B ELSE minOut = 0 > Byte(minOut) < 255
   IF minOut GE maxout THEN Message, 'OMIN must be less than OMAX.'

   ; Gamma must be greater than 0.
   IF N_Elements(gamma) EQ 0 THEN gamma = 1.0D ELSE gamma = 1.0e-6 > Double(gamma)

   ; Perform initial scaling of the image.
   output = Scale_Vector(Temporary(output), 0.0D, 1.0D, MinValue=imageMin, MaxValue=imageMax, /NAN, Double=1)

   ; For gamma, we need positive values. Make sure we have them
   IF Min(output) LT 0.0D THEN output = output + Abs(Min(output))
   output = Scale_Vector(output^gamma, minOut, maxOut, /NAN, Double=1)

   ; Does the user want the negative result?
   IF Keyword_Set(negative) THEN RETURN, BYTE(0B > (maxout - Round(output) + minOut) < 255B) $
      ELSE RETURN, BYTE(0B > Round(output) < 255B)

END