;+
; NAME:
;       LOGSCL
;
; PURPOSE:
;
;       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.
;
; 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:
;
;       outputImage = LOGSCL(image)
;
; ARGUMENTS:
;
;       image:         The image to be scaled. Written for 2D images, but arrays
;                      of any size are treated alike.
;
; KEYWORDS:
;
;       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:
;       None.
;
; EXAMPLES:
;
;       LoadCT, 0                                    ; Gray-scale colors.
;       image = LoadData(22)                         ; Load image.
;       TV, image                                    ; No contrast.
;       TV, LogScl(image)                            ; Improved contrast.
;       TV, LogScl(image, Exponent=10, Mean=0.65)    ; Even more contrast.
;       TV, LogScl(image, /Negative, Exponent=5)     ; A negative image.
;
; RESTRICTIONS:
;
;     Requires SCALE_VECTOR from the Coyote Library:
;
;        http://www.dfanning.com/programs/scale_vector.pro
;
; MODIFICATION HISTORY:
;
;       Written by:  David W. Fanning, 20 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 LogScl, image, $
   EXPONENT=exponent, $
   MEAN=mean, $
   NEGATIVE=negative, $
   MAX=maxValue, $
   MIN=minValue, $
   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(exponent) EQ 0 THEN exponent = 4.0
   IF N_Elements(mean) EQ 0 THEN mean = 0.5 ELSE mean = 0.0 > mean < 1.0
   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.'

   ; Exponent must be greater than 0.
   exponent = 1.0e-6 > exponent

   ; Perform initial scaling of the image into 0 to 1.
   output = Scale_Vector(Temporary(output), 0.0D, 1.0D, MaxValue=maxValue, $
      MinValue=minValue, /NAN, Double=1)

   ; Too damn many floating underflow warnings, no matter WHAT I do! :-(
   thisExcept = !Except
   !Except = 0

   ; Log scaling.
   output = 1.0D / ((1.0D + (mean / (Temporary(output) > 1e-16))^exponent) > (1e-16))

   ; Scale to image coordinates.
   output = Scale_Vector(Temporary(output), minOut, maxOut, /NAN, Double=1)

   ; Clear math errors.
   void = Check_Math()
   !Except = thisExcept

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

END