USAGE: matchimage [-c colormode] infile1 [infile2] outfile
USAGE: matchimage [-h or -help]

-c ... colormode ... colorspace mode of processing; options are: rgb,
.................... hsi, lab or ycbcr; default=rgb
-m ... mean ........ desired mean in place of mean from infile2;
.................... comma separated triplet; 0<=floats<=1;
.................... default is no mean provided
-s ... std ......... desired std in place of std from infile2;
.................... comma separated triplet; 0<=floats<=1;
.................... default is no mean provided
.................... infile1 will be be processed to match that of infile2

PURPOSE: To match the brightness and contrast of one image to another image.

DESCRIPTION: MATCHIMAGE matches the brightness and contrast of one image (infile1) to that of another image (infile2). This is done via a linear transformation of each RGB channel or an intensity channel from another colorspace. The matching uses the mean and standard deviations from each image according to the equation: (I2-Mean2)/Std2 = (I1-Mean1)/Std1. This equation represents an normalized intensity such that it has zero mean and approximately the same range of values due to the division by the standard deviations. We solve this equation to form a linear transformation between I1 and I2 according to I2=A*I1+B, where A=(Std2/Std1) is the slope or gain and B=(Mean2-A*Mean1) is the intercept of bias. If no infile2 is provide and a (set of) mean(s) and standard deviation(s0 are provided in stead, then infile1 will be matched to the provided mean and standard deviation.

ARGUMENTS:

-c colormode ... COLORMODE is the colorspace mode of processing. The options are: rgb, hsi, lab or ycbcr. The default=rgb.

-m mean ... MEAN is the desired mean(s) in place of mean(s) from infile2. Values are optional comma separated triplets in range 0<=floats<=1. If only one value is provided (and no commas), it will be used for all channels or the other colorspaces' intensity channel. The default is no mean provided.

-s std ... STD is the desired standard deviation(s) in place of the standard deviation(s) from infile2. Values are optional comma separated triplets in range 0<=floats<=1. If only one value is provided (and no commas), it will be used for for all channels or the other colorspaces' intensity channel. The default is no mean provided.

NOTE: This script will not change colors, only the brightness and contrast. Therefore it is primarily to normalize similar images to each other as for example video sequences and not to color match completely different images.

CAUTION: This script may not be backward compatible before IM colorspace and grayscale changes prior to IM 6.8.6.0. I have not tested it for earlier releases. Let me know if anyone tries and it fails. See http://www.imagemagick.org/discourse-server/viewtopic.php?f=4&t=21269

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.