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CGIMGSCL

CGIMGSCL
  This function scales an image using the same keywords and scaling available in
  cgImage and cgStretch. Set the `Stretch` keyword for the types of image scaling
  or stretching available.
 

Categories


    Graphics, Utilities
   

Returns


    Returns a scaled image.
 

Params


    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


    Used to for image display::
      IDL> scaledImage = cgImgScl(image, Stretch=4, Exponent=2)
      IDL> cgImage, scaledImage[0:100, 200:400], /Keep_Aspect
   

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, 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.

Copyright


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



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