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cgcompressscl.pro
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; docformat = 'rst'
;
; NAME:
; cgCompressScl
;
; PURPOSE:
; This is a utility routine to perform a compression 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. See pages 68-70 in
; _Digital Image Processing with MATLAB_ by Gonzales, Wood, and Eddins.
; The function is used to improve contrast in images.
;
;******************************************************************************************;
; ;
; Copyright (c) 2015, by Fanning Software Consulting, Inc. All rights reserved. ;
; ;
; Redistribution and use in source and binary forms, with or without ;
; modification, are permitted provided that the following conditions are met: ;
; ;
; * Redistributions of source code must retain the above copyright ;
; notice, this list of conditions and the following disclaimer. ;
; * Redistributions in binary form must reproduce the above copyright ;
; notice, this list of conditions and the following disclaimer in the ;
; documentation and/or other materials provided with the distribution. ;
; * Neither the name of Fanning Software Consulting, Inc. nor the names of its ;
; contributors may be used to endorse or promote products derived from this ;
; software without specific prior written permission. ;
; ;
; THIS SOFTWARE IS PROVIDED BY FANNING SOFTWARE CONSULTING, INC. ''AS IS'' AND ANY ;
; EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES ;
; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT ;
; SHALL FANNING SOFTWARE CONSULTING, INC. BE LIABLE FOR ANY DIRECT, INDIRECT, ;
; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED ;
; TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; ;
; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ;
; ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ;
; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS ;
; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ;
;******************************************************************************************;
;
;+
; This is a utility routine to perform a compression 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. See pages 68-70 in
; _Digital Image Processing with MATLAB_ by Gonzales, Wood, and Eddins.
; The function is used to improve contrast in images. The equation being
; implemented before scaling between OMIN and OMAX is as follows::
;
; output = 1.0D / ((1.0D + (mean / (Temporary(input) > 1e-16))^exponent) > (1e-16))
;
; :Categories:
; Image Processing
;
; :Returns:
; A byte scaled image is returned.
;
; :Params:
; image: in, required
; The image to be scaled. Written for 2D images, but arrays of any size are treated alike.
;
; :Keywords:
; exponent: in, optional, type=float, default=4.0
; The exponent in the compression transformation. By default, 4.0.
;
; max: in, optional
; Any value in the input image greater than this value is set to this value
; before scaling.
;
; mean: in, optional, type=float, default=0.5
; 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.
;
; min: in, optional
; Any value in the input image less than this value is set to this value
; before scaling.
;
; negative, in, optional, type=boolean, default=0
; If set, the "negative" of the result is returned.
;
; omax: in, optional, type=byte, default=255
; The output image is scaled between OMIN and OMAX.
;
; omin: in, optional, type=byte, default=0
; The output image is scaled between OMIN and OMAX.
;
; :Examples:
; Examples of compression stretching::
; cgLoadCT, 0 ; Gray-scale colors.
; image = cgDemoData(22) ; Load image.
; cgImage, image ; No contrast.
; cgImage, cgCompressScl(image) ; Improved contrast.
; cgImage, cgCompressScl(image, Exponent=10, Mean=0.65) ; Even more contrast.
; cgImage, cgCompressScl(image, /Negative, Exponent=5) ; A negative image.
;
; :Author:
; FANNING SOFTWARE CONSULTING::
; David W. Fanning
; 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
;
; :History:
; Change 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).
; Renamed cgCompressScl from LogScl when I discoverd LogScl implemented the wrong scaling equation.
; See the documentation in the retired LogScl program for details. 27 March 2015. DWF.
;
; :Copyright:
; Copyright (c) 2006-2015, Fanning Software Consulting, Inc.
;-
FUNCTION cgCompressScl, image, $
EXPONENT=exponent, $
MEAN=mean, $
NEGATIVE=negative, $
MAX=maxValue, $
MIN=minValue, $
OMAX=maxOut, $
OMIN=minOut
; Return to caller on error.
On_Error, 2
; 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 = cgScaleVector(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
; Compression scaling.
output = 1.0D / ((1.0D + (mean / (Temporary(output) > 1e-16))^exponent) > (1e-16))
; Scale to image coordinates.
output = cgScaleVector(Temporary(output), minOut, maxOut, MinValue=0.0D, MaxValue=1.0D, /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