; docformat = 'rst' ; ; NAME: ; cgLogScl ; ; PURPOSE: ; This is a utility routine to perform a logarithmic transformation ; on an image. The shape of the transformation is similar to the gamma ; curve (see cgGmaScl), except that the shape of the gamma curve is ; variable, while the log curve is fixed. 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 logarithmic transformation ; on an image. The shape of the transformation is similar to the gamma ; curve (see cgGmaScl), except that the shape of the gamma curve is ; variable, while the log curve is fixed. The function is used to improve ; contrast in images. The equation being implemented before scaling between ; OMIN and OMAX is as follows:: ; ; output = constant * Log(1 + double(input)) ; ; :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: ; constant: in, optional, type=float, default=1.0 ; A contant value by which the log result is multiplied. ; ; max: in, optional ; Any value in the input image greater than this value is set to this value ; before scaling. ; ; 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, cgLogScl(image) ; Improved contrast. ; ; :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, 27 March 2015. DWF. ; ; :Copyright: ; Copyright (c) 2015, Fanning Software Consulting, Inc. ;- FUNCTION cgLogScl, image, $ CONSTANT=constant, $ 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(constant) EQ 0 THEN constant = 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.' ; 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 = constant * ALog(1 + output) ; 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