top cgImgScl

Graphics, Utilities

result = cgImgScl(image [, xsize] [, ysize] [, BOTTOM=integer] [, BETA=float] [, CLIP=float] [, CONSTANT=float] [, EXCLUDE=numeric] [, EXPONENT=float] [, GAMMA=float] [, /INTERPOLATE] [, MAXVALUE=varies] [, MEAN=float] [, /MINUS_ONE] [, MINVALUE=varies] [, MISSING_INDEX=integer] [, MISSING_VALUE=integer] [, MULTIPLIER=float] [, NCOLORS=integer] [, /NEGATIVE] [, /SCALE] [, STRETCH=integer/string] [, SIGMA=float] [, TOP=integer])

Return value

Parameters

image in required

The input image that is to be scaled. Only 2D images can be scaled, although true-color images can be resized.

xsize in optional

The output X size of the image.

ysize in optional

The output Y size of the image.

Keywords

BOTTOM in optional type=integer default=0

If the SCALE keyword is set, the image is scaled before display so that all displayed pixels have values greater than or equal to BOTTOM and less than or equal to TOP.

BETA in optional type=float default=3.0

The beta factor in a Hyperpolic Sine stretch.

CLIP in optional type=float default=2

A number between 0 and 50 that indicates the percentage of pixels to clip off either end of the image histogram before performing a linear stretch.

CONSTANT in optional type=float default=1.0

A constant value applied in a logarithmic stretch.

EXCLUDE in optional type=numeric

The value to exclude in a standard deviation stretch.

EXPONENT in optional type=float default=4.0

The logarithm exponent in a compression stretch.

GAMMA in optional type=float default=1.5

The gamma factor in a gamma stretch.

INTERPOLATE in optional type=boolean default=0

Set this keyword to interpolate with bilinear interpolation the display image as it is sized to its final position in the display window. Interpolation will potentially create image values that do not exist in the original image. The default is to do no interpolation, so that image values to not change upon resizing. Interpolation can result in smoother looking final images.

MAXVALUE in optional type=varies

If this value is defined, the data is linearly scaled between MINVALUE and MAXVALUE. MAXVALUE is set to MAX(image) by default. Setting this keyword to a value automatically sets SCALE to 1. If the maximum value of the image is greater than 255, this keyword is defined and SCALE=1.

MEAN in optional type=float default=0.5

The mean factor in a compression stretch.

MINUS_ONE in optional type=boolean default=0

The value of this keyword is passed along to the cgResizeImage command. It prevents cgResizeImage from adding an extra row and column to the resulting array, which can be a problem with small image arrays.

MINVALUE in optional type=varies

If this value is defined, the data is linearly scaled between MINVALUE and MAXVALUE. MINVALUE is set to MIN(image) by default. Setting this keyword to a value automatically sets SCALE=1. If the minimum value of the image is less than 0, this keyword is defined and SCALE=1.

MISSING_INDEX in optional type=integer default=255

The index of the missing color in the final byte scaled image.

MISSING_VALUE in optional type=integer

The number that represents the missing value in the image.

MULTIPLIER in optional type=float

The multiplication factor in a standard deviation stretch. The standard deviation is multiplied by this factor to produce the thresholds for a linear stretch.

NCOLORS in optional type=integer default=256

If this keyword is supplied, the TOP keyword is ignored and the TOP keyword is set equal to NCOLORS-1. This keyword is provided to make cgImgScl easier to use with the color-loading programs such as cgLOADCT:

cgLoadCT, 5, NColors=100, Bottom=100 scaled = cgImgScl(image, NColors=100, Bottom=100)

Setting this keyword to a value automatically sets SCALE=1 and STRETCH='LINEAR', if not defined otherwise. Available only with 2D images.

NEGATIVE in optional type=boolean default=0

Set this keyword if you want to display the image with a negative or reverse stretch.

SCALE in optional type=boolean default=0

Set this keyword to byte scale the image before display. If this keyword is not set, the image is not scaled before display. This keyword will be set automatically by using any of the keywords normally associated with byte scaling an image.

STRETCH in optional type=integer/string default=0

The type of scaling performed prior to display. May be specified as a number or as a string (e.g, 3 or "Log"). Available only with 2D images. If Min(image) is less than zero or Max(image) is greater than 255, then the default value for stretch is 1.

Number Type of Stretch:

0 None No scaling whatsoever is done. 1 Linear scaled = BytScl(image, MIN=minValue, MAX=maxValue) 2 Linear 2% A histogram stretch, with a percentage of pixels clipped at both the top and bottom 3 Gamma scaled = cgGmaScl(image, MIN=minValue, MAX=maxValue, Gamma=gamma) 4 Log scaled = cgLogScl(image, MIN=minValue, MAX=maxValue, Mean=mean, Exponent=exponent) 5 Asinh scaled = cgAsinhScl(image, MIN=minValue, MAX=maxValue, Beta=beta) 6 SquareRoot A linear stretch of the square root histogram of the image values. 7 Equalization A linear stretch of the histogram equalized image histogram. 8 Gaussian A Gaussian normal function is applied to the image histogram. 9 MODIS Scaling done in the differential manner of the MODIS Rapid Response Team and implemented in the Coyote Library routine ScaleModis. 10 StdDev Standard deviation stretch. scaled = cgSDevScl(image, MULTIPLIER=2). 11 Compression Compress mid-tones in image with cgCompressScl.

SIGMA in optional type=float default=1.0

The sigma scale factor in a Gaussian stretch.

TOP in optional type=integer default=255

If the SCALE keyword is set, the image is scaled before display so that all displayed pixels have values greater than or equal to BOTTOM and less than or equal to TOP.

Examples

Author information

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

Copyright:

Copyright (c) 2012-2015, Fanning Software Consulting, Inc.

History:

Change History:

Written by David W. Fanning, 21 September 2012. Only define MISSING_INDEX value if needed. Change to support TRANSPARENT keyword in cgImage. 18 October 2012. DWF. Only 2D images can be scaled. 18 October 2012. DWF. Made LOG stretch a real log stretch and add a compression stretch. 27 March 2015. DWF.