/**
* im_buildlut:
* @input: input mask
* @output: output image
*
* This operation builds a lookup table from a set of points. Intermediate
* values are generated by piecewise linear interpolation.
*
* For example, consider this 2 x 2 matrix of (x, y) coordinates:
*
* <tgroup cols='2' align='left' colsep='1' rowsep='1'>
* <tbody>
* <row>
* <entry>0</entry>
* <entry>0</entry>
* </row>
* <row>
* <entry>255</entry>
* <entry>100</entry>
* </row>
* </tbody>
* </tgroup>
*
* We then generate:
*
* <tgroup cols='2' align='left' colsep='1' rowsep='1'>
* <thead>
* <row>
* <entry>Index</entry>
* <entry>Value</entry>
* </row>
* </thead>
* <tbody>
* <row>
* <entry>0</entry>
* <entry>0</entry>
* </row>
* <row>
* <entry>1</entry>
* <entry>0.4</entry>
* </row>
* <row>
* <entry>...</entry>
* <entry>etc. by linear interpolation</entry>
* </row>
* <row>
* <entry>255</entry>
* <entry>100</entry>
* </row>
* </tbody>
* </tgroup>
*
* This is then written as the output image, with the left column giving the
* index in the image to place the value.
*
* The (x, y) points don't need to be sorted: we do that. You can have
* several Ys, each becomes a band in the output LUT. You don't need to
* start at zero, any integer will do, including negatives.
*
* See also: im_identity(), im_invertlut().
*
* Returns: 0 on success, -1 on error
*/
int
im_buildlut( DOUBLEMASK *input, IMAGE *output )
{
State state;
if( !input || input->xsize < 2 || input->ysize < 1 ) {
im_error( "im_buildlut", "%s", _( "bad input matrix size" ) );
return( -1 );
}
if( build_state( &state, input ) ||
buildlut( &state ) ) {
free_state( &state );
return( -1 );
}
im_initdesc( output,
state.lut_size, 1, input->xsize - 1,
IM_BBITS_DOUBLE, IM_BANDFMT_DOUBLE,
IM_CODING_NONE, IM_TYPE_HISTOGRAM, 1.0, 1.0, 0, 0 );
if( im_setupout( output ) ||
im_writeline( 0, output, (PEL *) state.buf ) ) {
free_state( &state );
return( -1 );
}
free_state( &state );
return( 0 );
}
void fconfig_setgamma(FakerConfig &fc, double gamma)
{
fc.gamma = gamma;
buildlut(fc);
}
