143 lines
3.9 KiB
Groff
143 lines
3.9 KiB
Groff
.TH IM_HISTGR 3 "10 May 1991"
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.SH NAME
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im_histcum,
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im_histeq,
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im_histgr,
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im_histnD,
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im_histnorm,
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im_histspec,
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im_identity,
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im_identity_ushort,
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im_ismonotonic
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\- create, display and process histograms or luts
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.SH SYNOPSIS
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#include <vips/vips.h>
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int im_histgr( in, out, bandno )
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.br
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IMAGE *in, *out;
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.br
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int bandno;
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int im_histnD( in, out, bins )
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.br
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IMAGE *in, *out;
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.br
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int bins;
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int im_histcum(hist, lut)
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.br
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IMAGE *hist, *lut;
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int im_histnorm(hist, lut)
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.br
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IMAGE *hist, *lut;
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int im_histeq(hist, lut)
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.br
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IMAGE *hist, *lut;
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int im_histspec(histin, histref, lut)
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.br
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IMAGE *histin, *histref, *lut;
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int im_identity(lut, bands)
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.br
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IMAGE *lut;
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.br
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int bands;
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int im_identity_ushort(lut, bands, sz)
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.br
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IMAGE *lut;
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.br
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int bands;
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.br
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int sz;
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int im_ismonotonic( IMAGE *lut, int *out )
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.SH DESCRIPTION
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.B im_histgr(3)
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writes the histogram of image in to image out. If bandno is -1,
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then out will have the same number of bands as in, and each band of out will
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have the histogram of the corresponding band of in. Otherwise, bandno selects
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the band of the image for which the histogram will be found, numbering from
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zero.
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Image in may be either FMTUCHAR or FMTUSHORT. If in is uchar, then out will
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have 256 elements, one for each possible pixel value. If in is ushort, then
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.B im_histgr(3)
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finds the maximum of in, and outputs a histogram with max + 1
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elements.
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For example, suppose you have an image from a 12-bit camera, where
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each pixel is in the range [0,4095]. Calling
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.B im_histgr(3)
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for this image will
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make a histogram with at most 4096 elements. If the histogram is smaller than
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this, then it means that the right hand end of the histogram was all zero, and
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has not been generated.
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Also check
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.B im_histnD(3)
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below for another way to make histograms.
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.B im_histnD(3)
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makes a n-dimensional histogram from an n-band image (1, 2 and 3 bands only).
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Because 3D histograms can get very large very quickly, the
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.B bins
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parameter sets the length of each dimension, that is, the number of bins the
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possible numeric range of the image is divided into.
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Unsigned 8 and 16 bit images only.
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Use
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.B im_histplot(3)
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to graph the histogram for visualisation. See the separate manpage.
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.B im_histcum(3)
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forms a cumulative histogram.
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.B im_histnorm(3)
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normalises a histogram. The maximum histogram value becomes equal to the
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number of pixels in the histogram. In effect, the histogram
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becomes 'square'. Each channel is normalised separately.
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.B im_histeq(3)
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takes as input a histogram held by the IMAGE descriptor hist and creates an
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unsigned char look up table (held by the IMAGE descriptor lut) which when
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applied on the original image, (with histogram held by hist) histogram
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equalises it. Histogram equalisation is carried out for each band of hist
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individually.
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.B im_histspec(3)
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creates a lut for transforming an image with histogram held by histin
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according to the pdf (probability density function) of a reference image with
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histogram held by histref. histin and histref should have the same number
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of bands.
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.B im_identity(3)
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creates an look-up-table with Xsize=256, Ysize=1, Bands=bands, Bbits=BBBYTE,
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BandFmt=FMTUCHAR, Type=LUT, which is held by the IMAGE descriptor lut. The
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created image consist a bands linear (ramp) lut and is the basis for building
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look-up tables.
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.B im_identity_ushort(3)
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creates an look-up-table with Xsize=sz, Ysize=1, Bands=bands, Bbits=BBSHORT,
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BandFmt=FMTUSHORT, Type=LUT, which is held by the IMAGE descriptor lut. The
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created image consist of a linear (ramp) lut and is the basis for building
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look-up tables.
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.B im_ismonotonic(3)
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sets out to non-zero if the look-up table (or histogram) in lut is monotonic,
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that is, if it's slope is always >0.
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.SH RETURN VALUE
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All functions return 0 on success and -1 on error.
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.SH SEE ALSO
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im_hist(3), im_hsp(3), im_heq(3), im_maplut(3), im_tone_map(3),
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im_histplot(3).
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.SH COPYRIGHT
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The National Gallery and Birkbeck College, 1991 \- 1994.
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