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hist hacking

This commit is contained in:
John Cupitt 2010-03-24 22:00:39 +00:00
parent f30e7c113b
commit 81c6456b78
1 changed files with 63 additions and 16 deletions
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79
libvips/histograms_lut/im_invertlut.c
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@ -1,22 +1,12 @@
/* @(#) Given a mask of target values and real values, generate a LUT which
* @(#) will map reals to targets. Handy for linearising images from
* @(#) measurements of a colour chart. All values in [0,1]. Piecewise linear
* @(#) interpolation, extrapolate head and tail to 0 and 1.
* @(#)
* @(#) Eg. input line like:
* @(#)
* @(#) 0.1 0.2 0.3 0.1
* @(#)
* @(#) means a patch with 10% reflectance produces an image with 20% in
* @(#) channel 1, 30% in channel 2, and 10% in channel 3.
* @(#)
* @(#) Inputs don't need to be sorted (we do that). Generate any precision
* @(#) LUT ... typically ask for 256 elements.
/* invert a lut
*
* Written on: 5/6/01
* Modified on :
*
* 7/7/03 JC
* - generate image rather than doublemask (arrg)
* 23/3/10
* - gtkdoc
*/
/*
@ -236,16 +226,73 @@ invertlut( State *state )
return( 0 );
}
/**
* im_invertlut:
* @input: input mask
* @output: output LUT
* @lut_size: generate this much
*
* Given a mask of target values and real values, generate a LUT which
* will map reals to targets. Handy for linearising images from
* measurements of a colour chart. All values in [0,1]. Piecewise linear
* interpolation, extrapolate head and tail to 0 and 1.
*
* Eg. input like this:
*
* <tgroup cols='4' align='left' colsep='1' rowsep='1'>
* <tbody>
* <row>
* <entry>4</entry>
* <entry>3</entry>
* </row>
* <row>
* <entry>0.1</entry>
* <entry>0.2</entry>
* <entry>0.3</entry>
* <entry>0.1</entry>
* </row>
* <row>
* <entry>0.2</entry>
* <entry>0.4</entry>
* <entry>0.4</entry>
* <entry>0.2</entry>
* </row>
* <row>
* <entry>0.7</entry>
* <entry>0.5</entry>
* <entry>0.6</entry>
* <entry>0.3</entry>
* </row>
* </tbody>
* </tgroup>
*
* Means a patch with 10% reflectance produces an image with 20% in
* channel 1, 30% in channel 2, and 10% in channel 3, and so on.
*
* Inputs don't need to be sorted (we do that). Generate any precision
* LUT, typically you might ask for 256 elements.
*
* It won't work too well for non-monotonic camera responses
* (we should fix this). Interpolation is simple piecewise linear; we ought to
* do something better really.
*
* See also: im_buildlut(), im_invertlut()
*
* Returns: 0 on success, -1 on error
*/
int
im_invertlut( DOUBLEMASK *input, IMAGE *output, int lut_size )
{
State state;
if( !input || input->xsize < 2 || input->ysize < 1 ) {
if( !input ||
input->xsize < 2 ||
input->ysize < 1 ) {
im_error( "im_invertlut", "%s", _( "bad input matrix" ) );
return( -1 );
}
if( lut_size < 1 || lut_size > 65536 ) {
if( lut_size < 1 ||
lut_size > 65536 ) {
im_error( "im_invertlut", "%s", _( "bad lut_size" ) );
return( -1 );
}