53 lines
1.9 KiB
Groff
53 lines
1.9 KiB
Groff
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.TH IM_LITECOR 3 "5 December 1991"
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.SH NAME
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im_litecor \- perform light correction
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.SH SYNOPSIS
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.B #include <vips/vips.h>
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.B int im_litecor(in, white, out, clip, factor)
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.br
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.B IMAGE *in, *out;
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.br
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.B int clip;
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.br
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.B double factor;
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.SH DESCRIPTION
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.B im_litecor(3)
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performs light correction on the image held by the IMAGE descriptor in,
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with respect to a reference white image held by the IMAGE descriptor white.
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The result is written onto the IMAGE descriptor out. The function works
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on byte one channel images only.
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The flag clip can take two values 0 and 1. If clip is 1 then the input is
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corrected with reference to the maximum value of white (maxw) as follows.
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pel_out = factor * pel_in * maxw / pel_white.
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If clip is 0 then the output is scaled with the maximum possible output set
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to 255. In this case factor is not used but it must be set to a dummy value.
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The basic reason for lighting correction is that the input frame does not
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have a uniform distribution of white light due to the optical response of
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the lens. The function accepts a white image which is a simple multiple
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of the input image in size; for example it is possible that the white
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is a subsampled version of in; however the sizes of in must be an exact
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multiple of the white. If clip is set to 0, lighting correction is
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carried out and the result is scaled between 0 and 255. This can be used
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to correct individual frames.
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If multiband images are grabbed, then flag should be set to 1, since
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no scaling must be done. In this case the factor can reduce the number of
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clipped pels if overshooting occurs in the brightest band. The program
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prints the number of clipped pels with im_warning(3).
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.SH RETURN VALUE
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The function returns 0 on success and -1 on error.
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.SH BUGS
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clip==0 case not working too well.
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.SH SEE\ ALSO
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im_add(3), im_lintra(3), im_multiply(3).
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.SH COPYRIGHT
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.br
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N. Dessipris
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.SH AUTHOR
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N. Dessipris \- 05/12/1991
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