gstreamer/subprojects/gst-plugins-bad/gst/dvbsubenc/libimagequant/blur.c

#include "libimagequant.h"
#include "pam.h"
#include "blur.h"

/*
 Blurs image horizontally (width 2*size+1) and writes it transposed to dst (called twice gives 2d blur)
 */
static void
transposing_1d_blur (unsigned char *restrict src, unsigned char *restrict dst,
    unsigned int width, unsigned int height, const unsigned int size)
{
  for (unsigned int j = 0; j < height; j++) {
    unsigned char *restrict row = src + j * width;

    // accumulate sum for pixels outside line
    unsigned int sum;
    sum = row[0] * size;
    for (unsigned int i = 0; i < size; i++) {
      sum += row[i];
    }

    // blur with left side outside line
    for (unsigned int i = 0; i < size; i++) {
      sum -= row[0];
      sum += row[i + size];

      dst[i * height + j] = sum / (size * 2);
    }

    for (unsigned int i = size; i < width - size; i++) {
      sum -= row[i - size];
      sum += row[i + size];

      dst[i * height + j] = sum / (size * 2);
    }

    // blur with right side outside line
    for (unsigned int i = width - size; i < width; i++) {
      sum -= row[i - size];
      sum += row[width - 1];

      dst[i * height + j] = sum / (size * 2);
    }
  }
}

/**
 * Picks maximum of neighboring pixels (blur + lighten)
 */
LIQ_PRIVATE void
liq_max3 (unsigned char *src, unsigned char *dst, unsigned int width,
    unsigned int height)
{
  unsigned int i, j;

  for (j = 0; j < height; j++) {
    const unsigned char *row = src + j * width;
    unsigned char t1, t2;
    unsigned char prev, curr, next;

    const unsigned char *prevrow = src + (j > 1 ? j - 1 : 0) * width;
    const unsigned char *nextrow = src + MIN (height - 1, j + 1) * width;

    curr = row[0];
    next = row[0];

    for (i = 0; i < width - 1; i++) {
      prev = curr;
      curr = next;
      next = row[i + 1];

      t1 = MAX (prev, next);
      t2 = MAX (nextrow[i], prevrow[i]);
      *dst++ = MAX (curr, MAX (t1, t2));
    }

    t1 = MAX (curr, next);
    t2 = MAX (nextrow[width - 1], prevrow[width - 1]);
    *dst++ = MAX (t1, t2);
  }
}

/**
 * Picks minimum of neighboring pixels (blur + darken)
 */
LIQ_PRIVATE void
liq_min3 (unsigned char *src, unsigned char *dst, unsigned int width,
    unsigned int height)
{
  unsigned int j;

  for (j = 0; j < height; j++) {
    unsigned char t1, t2;
    const unsigned char *row = src + j * width,
        *prevrow = src + (j > 1 ? j - 1 : 0) * width,
        *nextrow = src + MIN (height - 1, j + 1) * width;

    unsigned char prev, curr = row[0], next = row[0];

    for (unsigned int i = 0; i < width - 1; i++) {
      prev = curr;
      curr = next;
      next = row[i + 1];

      t1 = MIN (prev, next);
      t2 = MIN (nextrow[i], prevrow[i]);
      *dst++ = MIN (curr, MIN (t1, t2));
    }

    t1 = MIN (curr, next);
    t2 = MIN (nextrow[width - 1], prevrow[width - 1]);
    *dst++ = MIN (t1, t2);
  }
}

/*
 Filters src image and saves it to dst, overwriting tmp in the process.
 Image must be width*height pixels high. Size controls radius of box blur.
 */
LIQ_PRIVATE void
liq_blur (unsigned char *src, unsigned char *tmp, unsigned char *dst,
    unsigned int width, unsigned int height, unsigned int size)
{
  assert (size > 0);
  if (width < 2 * size + 1 || height < 2 * size + 1) {
    return;
  }
  transposing_1d_blur (src, tmp, width, height, size);
  transposing_1d_blur (tmp, dst, height, width, size);
}