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cgclipscl.pro
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; docformat = 'rst'
;
; NAME:
; cgClipScl
;
; PURPOSE:
; This is a utility routine to perform linear scaling (similar to BYTSCL)
; on image arrays. If differs from BYTSCL only in that a user-specified
; percentage of pixels can be clipped from the image histogram, prior to
; scaling. By default, two percent of the pixels are clipped. Clipping
; occurs at both ends of the image histogram.
;
;******************************************************************************************;
; ;
; 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 linear scaling (similar to BYTSCL)
; on image arrays. If differs from BYTSCL only in that a user-specified
; percentage of pixels can be clipped from the image histogram, prior to
; scaling. By default, two percent of the pixels are clipped. Clipping
; occurs at both ends of the image histogram.
;
; :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.
;
; clip: in, optional, type=float, default=2.0
; The percent of image clipping. Must be value between 0 and 49. Clipping
; occurs from both ends of image histogram, so a clip of 2.0 linearly scales
; approximately 96% of the image histogram. Clipping percents are approximations
; only, and depend entirely on the distribution of pixels in the image. For
; interactive scaling, see cgStretch.
;
; :Keywords:
; 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.
;
; threshold: out, optional
; A two-element array containing the image thresholds that were used for the clipping.
;
; :Examples:
; To display a clipped image::
; cgLoadCT, 0 ; Gray-scale colors.
; image = cgDemoData(22) ; Load image.
; cgImage, cgClipScl(image, 4)
;
; :Author:
; FANNING SOFTWARE CONSULTING::
; David W. Fanning
; 1645 Sheely Drive
; Fort Collins, CO 80526 USA
; Phone: 970-221-0438
; E-mail: [email protected]
; Coyote's Guide to IDL Programming: http://www.idlcoyote.com
;
; :History:
; Change History::
; Written by: David W. Fanning, 6 September 2007.
; Not sure what this program was doing, but not what I thought. I've reworked
; the algorithm to scale the data appropriately. 25 Oct 2011. DWF.
; Renamed cgClipScl from ClipScl. 27 March 2015. DWF.
;
; :Copyright:
; Copyright (c) 2007-2015, Fanning Software Consulting, Inc.
;-
FUNCTION cgClipScl, image, clip, $
NEGATIVE=negative, $
OMAX=maxOut, $
OMIN=minOut, $
THRESHOLD=threshold
; Return to caller on error.
;On_Error, 2
Catch, theError
IF theError NE 0 THEN BEGIN
Catch, /Cancel
void = cgErrorMsg()
RETURN, vector
ENDIF
; Check arguments.
IF N_Elements(image) EQ 0 THEN Message, 'Must pass IMAGE argument.'
IF N_Elements(clip) EQ 0 THEN clip = 2 ELSE clip = 0 > clip < 48
; 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 = image
; Check keywords.
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.'
; Calculate binsize.
maxr = Max(image, MIN=minr, /NAN)
range = maxr - minr
IF Size(image, /TName) EQ 'BYTE' THEN binsize = 1.0 ELSE binsize = range / 1000.
IF Size(image, /TName) NE Size(binsize, /TName) THEN image = Convert_To_Type(image, Size(binsize, /TName))
h = Histogram(image, BINSIZE=binsize, OMIN=omin, OMAX=omax, /NAN)
n = N_Elements(image)
cumTotal = Total(h, /CUMULATIVE)
minIndex = Value_Locate(cumTotal, n * (clip/100.))
IF minIndex EQ -1 THEN minIndex = 0
WHILE cumTotal[minIndex] EQ cumTotal[minIndex + 1] DO BEGIN
minIndex = minIndex + 1
ENDWHILE
minThresh = minIndex * binsize + omin
; Not all files can be clipped appropriately. If maxIndex
; is -1 or N_Elements(cumTotal), or maxIndex=minIndex then
; just byte scale the image and get out of here.
maxIndex = Value_Locate(cumTotal, n * ((100-clip)/100.))
IF (maxIndex EQ -1) || (maxIndex EQ N_Elements(cumTotal)) || (maxIndex EQ minIndex) THEN BEGIN
threshold = [minr, maxr]
Message, 'Image histogram could not be clipped successfully. Image is byte scaled.', /Informational
IF Keyword_Set(negative) THEN RETURN, 255B - BytScl(image, /NAN) ELSE RETURN, BytScl(image, /NAN)
ENDIF
; If you are still here, try to clip the histogram.
WHILE cumTotal[maxIndex] EQ cumTotal[maxIndex - 1] DO BEGIN
maxIndex = maxIndex - 1
ENDWHILE
maxThresh = maxIndex * binsize + omin
; Save the thresholds.
threshold = [minThresh, maxThresh]
; Scale the data.
output = cgScaleVector(Temporary(output), MIN=threshold[0], MAX=threshold [1], minOut, maxOut)
IF Keyword_Set(negative) THEN RETURN, 0B > (maxout - output + minOut) < 255B $
ELSE RETURN, output
END