42 lines
1.1 KiB
Groff
42 lines
1.1 KiB
Groff
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.TH IM_INVERTLUT 3 "June 2001"
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.SH NAME
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im_invertlut \- turn a set of greyscale measurements into a gamma-correcting
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LUT
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.SH SYNOPSIS
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#include <vips/vips.h>
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int
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.br
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im_invertlut( DOUBLEMASK *input, IMAGE *output, int lut_size )
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.SH DESCRIPTION
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Given a mask of target values and real values, generate a LUT which
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will map reals to targets. Handy for linearising images from
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measurements of a colour chart. All values in [0,1].
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Extrapolate head and tail to 0 and 1.
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Eg. input like:
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4 3
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0.1 0.2 0.3 0.1
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0.2 0.4 0.4 0.2
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0.7 0.5 0.6 0.3
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means a patch with 10% reflectance produces an image with 20% in
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channel 1, 30% in channel 2, and 10% in channel 3. A patch with 20%
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reflectance makes an image with 40% red, 40% green and 20% blue, and so on.
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Inputs don't need to be sorted (we do that). Generate any precision
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LUT ... typically ask for 256 elements.
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It won't work too well for non-monotonic camera responses (should fix this).
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Interpolation is simple piecewise linear; ought to do something better really.
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.SH RETURN VALUE
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-1 on error, otherwise 0
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.SH SEE ALSO
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im_histgr(3), im_hsp(3), im_heq(3), im_identity(3).
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.SH COPYRIGHT
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2001, National Gallery
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