Geografic-Information-System/lib/gis/color_hist.c

/**********************************************************************
 *
 *  G_make_histogram_eq_colors (colors, statf)
 *
 *   struct Colors *colors      struct to hold colors
 *   struct Cell_stats *statf   cell stats info
 *
 *  Generates histogram equalized grey scale from
 *  cell stats structure info.
 *  Color range is 0-255.
 *
 **********************************************************************
 *
 *  G_make_histogram_log_colors (colors, statf, min, max)
 *
 *   struct Colors *colors      struct to hold colors
 *   struct Cell_stats *statf   cell stats info
 *
 *  Generates histogram with normalized log transformed grey scale from
 *  cell stats structure info.
 *  Color range is 0-255.
 *
 **********************************************************************/
#include <grass/gis.h>
#include <math.h>


/*!
 * \brief make histogram-stretched grey colors
 *
 * Generates a histogram
 * contrast-stretched grey scale color table that goes from the ,histogram
 * information in the Cell_stats structure <b>s.</b>  (See
 * Raster_Histograms).
 *
 *  \param colors
 *  \param s
 *  \return
 */

void G_make_histogram_eq_colors(struct Colors *colors,
				struct Cell_stats *statf)
{
    long count, total;
    CELL prev = 0, cat;
    double span, sum;
    int first;
    int x, grey;
    int R, G, B;

    G_init_colors(colors);

    G_str_to_color(DEFAULT_BG_COLOR, &R, &G, &B);
    G_set_null_value_color(R, G, B, colors);

    total = 0;

    G_rewind_cell_stats(statf);
    while (G_next_cell_stat(&cat, &count, statf))
	if (count > 0)
	    total += count;
    if (total <= 0)
	return;

    span = total / 256.0;
    first = 1;
    grey = 0;
    sum = 0.0;

    G_rewind_cell_stats(statf);
    while (G_next_cell_stat(&cat, &count, statf)) {
	if (count <= 0)
	    continue;
	x = (sum + (count / 2.0)) / span;
	if (x < 0)
	    x = 0;
	else if (x > 255)
	    x = 255;
	sum += count;
	if (first) {
	    prev = cat;
	    grey = x;
	    first = 0;
	}
	else if (grey != x) {
	    G_add_color_rule(prev, grey, grey, grey, cat - 1, grey, grey,
			     grey, colors);
	    grey = x;
	    prev = cat;
	}
    }
    if (!first) {
	G_add_color_rule(prev, grey, grey, grey, cat, grey, grey, grey,
			 colors);
    }
}

void G_make_histogram_log_colors(struct Colors *colors,
				 struct Cell_stats *statf, int min, int max)
{
    long count, total;
    double lmin, lmax;
    CELL prev = 0, cat;
    int first;
    int x, grey;
    int R, G, B;

    G_init_colors(colors);

    G_str_to_color(DEFAULT_BG_COLOR, &R, &G, &B);
    G_set_null_value_color(R, G, B, colors);

    total = 0;

    G_rewind_cell_stats(statf);
    while (G_next_cell_stat(&cat, &count, statf))
	if (count > 0)
	    total += count;
    if (total <= 0)
	return;

    first = 1;
    grey = 0;

    lmin = log(min);
    lmax = log(max);

    G_rewind_cell_stats(statf);
    while (G_next_cell_stat(&cat, &count, statf)) {
	if (count <= 0)
	    continue;

	/* log transform normalized */
	x = (int)(255 * (log(cat) - lmin) / (lmax - lmin));

	if (x < 0)
	    x = 0;
	else if (x > 255)
	    x = 255;
	if (first) {
	    prev = cat;
	    grey = x;
	    first = 0;
	}
	else if (grey != x) {
	    G_add_color_rule(prev, grey, grey, grey, cat - 1, grey, grey,
			     grey, colors);
	    grey = x;
	    prev = cat;
	}
    }
    if (!first) {
	G_add_color_rule(prev, grey, grey, grey, cat, grey, grey, grey,
			 colors);
    }
}