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rgbtohsv.c

Go to the documentation of this file.

#include        "sadie.h"

/*-Copyright Information------------------------------------------------------*/
/* Copyright (c) 1988 by the University of Arizona Digital Image Analysis Lab */
/*----------------------------------------------------------------------------*/
/*-General Information--------------------------------------------------------*/
/*                                                                            */
/*   This function transforms a red-green-blue image                          */
/*   to a hue-saturation-value image.                                         */
/*                                                                            */
/*----------------------------------------------------------------------------*/
/*-Background Information-----------------------------------------------------*/
/*                                                                            */
/*   Smith, A.R.:                                                             */
/*   "Color Gamut Transform Pairs"                                            */
/*   Computer Graphics, Vol. 12, No. 3 (August 1978), pp. 12-19.              */
/*                                                                            */
/*----------------------------------------------------------------------------*/
/*-Interface Information------------------------------------------------------*/
void
RGBTOHSV (IMAGE * in,           /*  I   Pointer to the input image.                           */
          IMAGE ** out          /*  O   Address of a pointer to the output image.             */
          /*      The input image may be overwritten (out = &in).       */
/*----------------------------------------------------------------------------*/
  )
{
  register short j, k;
  char msg[SLEN];
  double r, g, b, h, s, v, pinc, psum;

  if (TIMES)
    TIMING (T_RGBTOHSV);
  if (NAMES)
    {
      MESSAGE ('I', "");
      MESSAGE ('I', "RGBTOHSV");
      MESSAGE ('I', "");
      sprintf (msg, " Input image:   %s", in->text);
      MESSAGE ('I', msg);
      MESSAGE ('I', " ...............");
    }

  /* check input */
  if (!CHECKIMG (in))
    {
      MESSAGE ('E', " Can't identify image.");
      goto the_end;
    }
  else if (in->nbnd != 3)
    {
      MESSAGE ('E', " Input image must be a three-band image.");
      goto the_end;
    }
  else if ((RANGE (in), in->gmin) < (PIXEL) 0)
    {
      MESSAGE ('E', " RGB components must be equal to or greater than zero.");
      goto the_end;
    }

  /* create image of appropriate size */
  if (!CHECKIMG (*out))
    GETMEM (in->nbnd, in->nlin, in->npix, out);
  if (!*out)
    goto the_end;

  /* initialize progress indicator */
  if (LINES && !PROGRESS (psum = 0.0))
    goto the_end;
  pinc = 1.0 / (double) in->nlin;

  /* transform RGB to HSV */
  for (j = 0; j < in->nlin; j++)
    {
      for (k = 0; k < in->npix; k++)
        {
          r = (double) in->data[0][j][k];
          g = (double) in->data[1][j][k];
          b = (double) in->data[2][j][k];
          v = (r > g ? r : g) > b ? (r > g ? r : g) : b;
          s = (r < g ? r : g) < b ? (r < g ? r : g) : b;
          (*out)->data[2][j][k] = (PIXEL) v;
          if (v == s)
            {
              (*out)->data[0][j][k] =
                j == 0 ? (PIXEL) SMIN : (*out)->data[0][j][k - 1];
              (*out)->data[1][j][k] = (PIXEL) SMIN;
            }
          else
            {
              if (r == v)
                {
                  h =
                    g ==
                    s ? 5.0 + (v - b) / (v - s) : 1.0 - (v - g) / (v - s);
                }
              else if (g == v)
                {
                  h =
                    b ==
                    s ? 1.0 + (v - r) / (v - s) : 3.0 - (v - b) / (v - s);
                }
              else              /* (b == s) */
                {
                  h =
                    r ==
                    s ? 3.0 + (v - g) / (v - s) : 5.0 - (v - r) / (v - s);
                }
              (*out)->data[0][j][k] = (PIXEL) (h / 6.0 * (double) SMAX);
              (*out)->data[1][j][k] = (PIXEL) ((v - s) / v * (double) SMAX);
            }
        }
      if (LINES && !PROGRESS (psum += pinc))
        goto the_end;
    }

the_end:
  if (TIMES)
    TIMING (T_EXIT);
}

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