USAGE: kneemap [-a amount] [-c channels] [-l lutlength] [-g] infile outfile
USAGE: kneemap [-h or -help]

-a .... amount ....... amount of curvature for knee curve mapping
...................... transformation; -1<float<1; positive values
...................... non-linearly brighten the image and negative values
...................... non-linearly darken the image; default=0 for no change
-c .... channels ..... any valid IM combination of channels corresponding to
...................... the image's colorspace to which to apply the
...................... transformation: r,g,b,a, or c,m,y,k,a;
...................... default=all non-alpha channels
-l .... lutlength .... length of 1D lut; integer>0; default=1000
-g ................... enables the creation of a graph of the knee curve
...................... mapping transformation, which is then displayed
...................... automatically. There is a default setting below that
...................... can be changed to enable this to be save to a file
...................... named outfile_kneegraph.gif rather than just viewed.

PURPOSE: To create a symmetric soft knee-shaped curved mapping look up table and applies it to an image.

DESCRIPTION: KNEEMAP creates a symmetric soft knee-shaped curved mapping transformation similar to -evaluate log or -evaluate pow (-gamma), but which is symmetric. This transformation is generated as 1D lut and applied to the image using -clut to affect the intensity/color transformation. The transformation is sensitive to the desired channels specified.

ARGUMENTS:

-a amount ... AMOUNT is the amount of curvature for knee curve mapping transformation. Values are in the range 1<float<1. Positive values non-linearly brighten the image and negative values non-linearly darken the image. The default=0 for no change.

-c channels ... CHANNELS are any valid IM combination of channels corresponding to the image's colorspace to which to apply the transformation. Combinations include: r,g,b,a, or c,m,y,k,a (with no commas). The

-l lutlength ... LUTLENGTH is the length of 1D lut. Values are integer>0. The default=1000

-g ... enables the creation of a graph of the knee curve mapping transformation, which is then displayed automatically. There is a default setting below that can be changed to enable this to be save to a file named outfile_kneegraph.gif. The graph will be scaled to size 100x100.

My thanks to Max Usatov for bringing the dynamic range compressor or soft knee compressor to my attention. See http://www.scribd.com/doc/14599153/Fast-Dynamic-Range-Compression-for-Grayscale-Images

REQUIREMENTS: IM 6.3.5-7 is required to support the use of -clut

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.