What do the numbers returned by

Question

Hi,

I have a script that is using

m = img << Get Pixels;

on a greyscale jpg image. The values returned range from about 0 to -13 million. It seems the 0s correspond to "black" and the high minuses to "white". I have been able to successfully use negative values of large magnitude to identify "white" areas of the image. However, I have been asked to document this script including what Get Pixels does. How does it determine these numbers? The scripting index says "If no color designator is specified, a matrix of JSL colors representing the pixel values is returned". What does 'JSL colors' mean exactly? Google has not been useful for this... :(

Craige_Hales · Accepted Answer

The negative numbers are the RGB values. Try this to see the pattern; run just the hex(...) line to see the following line in the log:

hex( -rgbcolor(0.0,0.0,0.0), "integer")
"00000000" black
//:*/
hex( -rgbcolor(0.0,0.0,1.0), "integer")
"000000FF" blue
//:*/
hex( -rgbcolor(0.0,1.0,0.0), "integer")
"0000FF00" green
//:*/
hex( -rgbcolor(1.0,0.0,0.0), "integer")
"00FF0000" red
//:*/
hex( -rgbcolor(1.0,1.0,1.0), "integer")
"00FFFFFF" white
//:*/
hex( -rgbcolor(0.5,0.0,0.0), "integer")
"00800000" dark red
//:*/
hex( -rgbcolor(0.0,0.25,0.0), "integer")
"00004000" darker green
//:*/
hex( -rgbcolor(0.0,0.0,0.01), "integer")
"00000003" really dark blue

rgbcolor(...) takes a red,green,blue argument and returns one of those negative JSL color values. Make it positive before passing to hex() to make everything clear. The bottom three bytes, represented by two hex digits each, represent the 256 possible levels of r,g,b.