rsstretch

From DavinciWiki

Contents: Description, Arguments, Usage, Examples, Images, Sub-Functions, Related Functions, Source

Description

Perform a running sigma stretch on every xy plane of the data (band independent).

rsstretch() performs an individual sigma stretch on every sub-section of the array defined by an x and y dimension. It then uses an overlap of half of the defined size to blend it with the next section of the data. This is done so there is no visible seam and the stretch is esentially "running" or changing over the whole data set. This process helps eliminate image wide variations and maximizes local variation producing a "harder" stretch. This is evident when looking at the sample images below.

Changing the x and y sizes will ultimately determine how local or regional features affect the stretch.

Uses thm.sstretch as the stretching function.

Arguments and Return Values

Arguments: Accepts any numeric array

Return Value: A stretched byte array

Usage

Syntax: rsstretch(data = VAR [, ignore = FLOAT] [, ysize = INT] [, xsize = INT] [, variance = FLOAT] [, verbose = BOOL])

'data' - Any numeric array

'ignore' - Ignore value of the black space. Default of -32768.

'ysize' - Any integer for beaking up the data in the y direction. Default of 1000.

'xsize' - Any integer for beaking up the data in the x direction. Default of 4000.

'variance' - variance of the stretch. Default of 40.

'verbose' - print the segment of the image that is being manipulated. Default is 0.

Examples

dv> a
829x3622x1 array of float, bsq format [12,010,552 bytes]

The two methods below are equivalent and yeild the same results, but the second can be used for more memory efficient processing.

dv> b = rsstretch(a,ysize=500,xsize=1000,ignore=-32768)
829x3622x1 array of byte, bip format [3,002,638 bytes]

dv> b=rsstretch(data=a,ysize=500,xsize=1000,ignore-=32768)
829x3622x1 array of byte, bip format [3,002,638 bytes]

Images

The stretch of the left image is dominated by the canyon's huge difference in values (visible as contrast) and consequently the plains appear washed out. The stretch on the right is more consistent throughout normalizing the plains above the canyon to have a similar stretch as the canyon itself.