CGCOMPRESSSCL
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.