;+ ; 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: david@idlcoyote.com ; Coyote's Guide to IDL Programming: http://www.idlcoyote.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: ; ; cgLoadCT, 0 ; Gray-scale colors. ; image = cgDemoData(22) ; Load image. ; cgImage, image ; No contrast. ; cgImage, LogScl(image) ; Improved contrast. ; cgImage, LogScl(image, Exponent=10, Mean=0.65) ; Even more contrast. ; cgImage, LogScl(image, /Negative, Exponent=5) ; A negative image. ; ; RESTRICTIONS: ; ; Requires cgScaleVector from the Coyote Library: ; ; http://www.idlcoyote.com/programs/cgScaleVector.pro ; ; MODIFICATION 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). ;- ;******************************************************************************************; ; Copyright (c) 2008, 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. ; ;******************************************************************************************; 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 = cgErrorMsg() 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 = 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 ; Log 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