Man Linux: Main Page and Category List


       im_histcum,  im_histeq, im_histgr, im_histnD, im_histnorm, im_histspec,
       im_identity, im_identity_ushort, im_ismonotonic - create,  display  and
       process histograms or luts


       #include <vips/vips.h>

       int im_histgr( in, out, bandno )
       IMAGE *in, *out;
       int bandno;

       int im_histnD( in, out, bins )
       IMAGE *in, *out;
       int bins;

       int im_histcum(hist, lut)
       IMAGE *hist, *lut;

       int im_histnorm(hist, lut)
       IMAGE *hist, *lut;

       int im_histeq(hist, lut)
       IMAGE *hist, *lut;

       int im_histspec(histin, histref, lut)
       IMAGE *histin, *histref, *lut;

       int im_identity(lut, bands)
       IMAGE *lut;
       int bands;

       int im_identity_ushort(lut, bands, sz)
       IMAGE *lut;
       int bands;
       int sz;

       int im_ismonotonic( IMAGE *lut, int *out )


       im_histgr(3)  writes  the histogram of image in to image out. If bandno
       is -1, then out will have the same number of bands as in, and each band
       of  out  will  have  the  histogram  of  the  corresponding band of in.
       Otherwise, bandno selects the band of the image for which the histogram
       will be found, numbering from zero.

       Image  in may be either FMTUCHAR or FMTUSHORT. If in is uchar, then out
       will have 256 elements, one for each possible pixel  value.  If  in  is
       ushort,  then  im_histgr(3)  finds  the  maximum  of  in, and outputs a
       histogram with max + 1 elements.

       For example, suppose you have an image from a 12-bit camera, where each
       pixel  is  in  the  range [0,4095]. Calling im_histgr(3) for this image
       will make a histogram with at most 4096 elements. If the  histogram  is
       smaller  than  this,  then  it  means  that  the  right hand end of the
       histogram was all zero, and has not been generated.

       Also check im_histnD(3) below for another way to make histograms.

       im_histnD(3) makes a n-dimensional histogram from an n-band image (1, 2
       and  3  bands  only).   Because  3D  histograms can get very large very
       quickly, the bins parameter sets the length of each dimension, that is,
       the  number  of bins the possible numeric range of the image is divided

       Unsigned 8 and 16 bit images only.

       Use im_histplot(3) to graph the histogram for  visualisation.  See  the
       separate manpage.

       im_histcum(3) forms a cumulative histogram.

       im_histnorm(3)  normalises  a  histogram.  The  maximum histogram value
       becomes equal to the number of pixels in the histogram. In effect,  the
       histogram becomes ’square’. Each channel is normalised separately.

       im_histeq(3)  takes  as  input a histogram held by the IMAGE descriptor
       hist and creates an unsigned char look up  table  (held  by  the  IMAGE
       descriptor  lut)  which  when  applied  on  the  original  image, (with
       histogram held by hist) histogram equalises it. Histogram  equalisation
       is carried out for each band of hist individually.

       im_histspec(3)  creates  a lut for transforming an image with histogram
       held by histin according to the pdf (probability density function) of a
       reference  image  with  histogram  held  by histref. histin and histref
       should have the same number of bands.

       im_identity(3)  creates  an  look-up-table   with  Xsize=256,  Ysize=1,
       Bands=bands, Bbits=BBBYTE, BandFmt=FMTUCHAR, Type=LUT, which is held by
       the IMAGE descriptor lut.  The created image  consist  a  bands  linear
       (ramp) lut and is the basis for building look-up tables.

       im_identity_ushort(3) creates an look-up-table  with Xsize=sz, Ysize=1,
       Bands=bands, Bbits=BBSHORT, BandFmt=FMTUSHORT, Type=LUT, which is  held
       by  the  IMAGE  descriptor  lut.  The created image consist of a linear
       (ramp) lut and is the basis for building look-up tables.

       im_ismonotonic(3) sets  out  to  non-zero  if  the  look-up  table  (or
       histogram) in lut is monotonic, that is, if it’s slope is always >0.


       All functions return 0 on success and -1 on error.


       im_hist(3),   im_hsp(3),   im_heq(3),   im_maplut(3),   im_tone_map(3),


       The National Gallery and Birkbeck College, 1991 - 1994.

                                  10 May 1991