SCALEMODIS Name
SCALEMODIS Purpose
MODIS corrected reflectance images often appear drab when initially processed
and displayed on a computer using BYTSCL. In fact, the resulting true-color
images look nothing like the images you can find on the MODIS Rapid Response
web page (http://rapidfire.sci.gsfc.nasa.gov/gallery/). After poking around on
the Internet for awhile, I discovered that the Rapid Response Team doesn't use
BYTSCL to prepare the images. Rather, they selectively scale portions of the
reflectance image, using a piecewise scaling with different slopes. This program
implements this Rapid Response Team algorithm.
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
Graphics
Calling Sequence
scaledBand = ScaleModis(red, green, blue)
Arguments
red: A two-dimensional array representing the corrected reflectance
values of a MODIS image. This is a required parameter. If the
green and blue parameters are also used, this parameter will
represent the red band of a RGB 24-bit scaled image that is returned.
green: If the three parameters--red, green, and blue--are present, the returned
array is a 24-bit true-color image, scaled appropriately. This parameter
is used as the green band in such an image. The parameter is a two-dimensional
array of corrected reflectance values.
blue: If the three parameters--red, green, and blue--are present, the returned
array is a 24-bit true-color image, scaled appropriately. This parameter
is used as the blue band in such an image. The parameter is a two-dimensional
array of corrected reflectance values.
Keyword Parameters
RANGE: A two-dimensional array that the input bands are first scaled into, prior to
the differential scaling using the MODIS Rapid Response algorithm. The default
input range is [-0.01, 1.10]. These values will be used to set the MIN and MAX
keywords for the BYTSCL command in the initial scaling of the input bands.
CLOUD: The MODIS Rapid Response team uses a slightly different scaling algorithm when
the idea is to emphasize clouds in a MODIS scene. Set this keyword to use the
alternate cloud scaling algorithm.
Outputs
scaledBand: If a single 2D array is passed as the argument, then scaledBand is the scaled
2D output array. If all three arguments are passed to the program, then scaledBand
is a scaled 24-bit image that represents a true-color or false color representation
of the three input bands.
Modification History
Written by: David W. Fanning, July 2009, using the IDL programs MODIS_FALSE_COLOR and
and SCALE_IMAGE for inspiration. I found these programs on the Internet when poking
around MODIS web pages. I suspect, but I am not sure, these programs were originally
written by Liam Gumley.
Minor changes to the ScaleIt function to be sure partitioning is done correctly. 5 Aug 2009. DWF.