Fixes in the algorithm that detects what type of transparency an imag…

…e has. (#8425)

src/grdimage.c

@@ -983,10 +983,10 @@ GMT_LOCAL void grdimage_img_set_transparency (struct GMT_CTRL *GMT, struct GRDIM
  */
  double o, t; /* o - opacity, t = transparency */
  gmt_M_unused (GMT);
- o = pix4 / 255.0; t = 1 - o;
  if (Conf->Transp->n_transp == 2)
  gmt_M_rgb_only_copy (rgb, Conf->tr_rgb);
  else { /* Blend */
+ o = pix4 / 255.0; t = 1 - o;
  if (Conf->invert) t = o, o = 1 - t;
  rgb[0] = o * rgb[0] + t * Conf->tr_rgb[0];
  rgb[1] = o * rgb[1] + t * Conf->tr_rgb[1];
@@ -1095,26 +1095,46 @@ GMT_LOCAL bool grdimage_transparencies (struct GMT_CTRL *GMT, struct GMT_IMAGE *
  struct GMT_GRID_HEADER *H = I->header; /* Pointer to the active image header */
  unsigned char *transparency; /* Pointer to memory where transparency resides */
  int64_t row, col, node;
- unsigned int k, tr, tr_max = 0, tr_min = 255, tr_band; /* tr_band is 0 if image has alpha channel, else 1 for gray and 3 for color */
+ unsigned int k, tr, tr_max = 0; /* tr_band is 0 if image has alpha channel, else 1 for gray and 3 for color */
  unsigned int n_bands = H->n_bands;
  gmt_M_unused (GMT);
 
  if (n_bands%2 == 1 && I->alpha == NULL) return false; /* No transparencies either in band 1 or 4 nor in alpha */
 
- tr_band = (I->alpha) ? 0 : n_bands - 1;
- transparency = (tr_band) ? I->data : I->alpha; /* Points to the data array with A */
- for (row = 0; row < H->n_rows; row++) { /* March along scanlines in the output bitimage */
- node = gmt_M_ijp (H, row, 0) + tr_band; /* Start pixel with 4 bytes of this image row */
- for (col = 0; col < H->n_columns; col++, node += n_bands) { /* March along this scanline in steps of 2 (gA) or 4 (RGBA) */
- tr = (unsigned int)transparency[node]; /* Get transparency values */
+ if (I->alpha) {
+ for (node = 0; node < H->nm; node++) { /* March along scanlines in the output bitimage */
+ tr = (unsigned int)I->alpha[node]; /* Get transparency values */
  if (opacity) tr = 255 - tr; /* Must flip from opacity to transparency */
  T->alpha_count[tr]++; /* Count frequency of transparency values */
  }
  }
+ else {
+ if (n_bands == 4 && H->mem_layout[2] == 'P') { /* RGBA Pixel interleaved */
+ for (row = 0; row < H->n_rows; row++) {
+ for (col = 0; col < H->n_columns; col++) {
+ node = gmt_M_ijp (H, row, col) * 4 + 3;
+ tr = (unsigned int)I->data[node];
+ if (opacity) tr = 255 - tr;
+ T->alpha_count[tr]++;
+ }
+ }
+ }
+ else { /* Band interleaved. Tansparency is in 4th band*/
+ node = H->size * (n_bands - 1); /* Either gray or color */
+ for (row = 0; row < H->n_rows; row++) {
+ for (col = 0; col < H->n_columns; col++) {
+ node += gmt_M_ijp (H, row, col);
+ tr = (unsigned int)I->data[node];
+ if (opacity) tr = 255 - tr;
+ T->alpha_count[tr]++;
+ }
+ }
+ }
+ }
+
  for (k = 0; k < GMT_LEN256; k++) { /* Determine how many different transparencies */
  if (T->alpha_count[k]) { /* Used at least once */
  T->n_transp++;
- if (T->alpha_count[k] < tr_min) tr_min = k; /* Keep track of smallest value */
  if (T->alpha_count[k] > tr_max) tr_max = k; /* Keep track of largest value */
  }
  }
@@ -1132,13 +1152,11 @@ GMT_LOCAL bool grdimage_transparencies (struct GMT_CTRL *GMT, struct GMT_IMAGE *
  T->value = 0;
  T->mode = 3;
  T->n_dominant = T->alpha_count[0];
- //fprintf (stderr, "Min A = %d [x %d] Max A = %d [x %d]\n", tr_min, T->alpha_count[tr_min], tr_max, T->alpha_count[tr_max]);
  }
  else {
  T->value = 255; /* Case 4: Like 3 but 255 most used of two transparency values */
  T->n_dominant = T->alpha_count[255];
  T->mode = 4;
- //fprintf (stderr, "Min A = %d [x %d] Max A = %d [x %d]\n", tr_min, T->alpha_count[tr_min], tr_max, T->alpha_count[tr_max]);
  }
  return (true);
 }
@@ -1213,7 +1231,7 @@ GMT_LOCAL void grdimage_img_c2s_no_intensity (struct GMT_CTRL *GMT, struct GRDIM
 GMT_LOCAL void grdimage_img_color_no_intensity (struct GMT_CTRL *GMT, struct GRDIMAGE_CTRL *Ctrl, struct GRDIMAGE_CONF *Conf, unsigned char *image) {
  /* Function that fills out the image in the special case of 1) image, 2) color, 3) with intensity */
  struct GMT_GRID_HEADER *H_s = Conf->Image->header; /* Pointer to the active data header */
- bool transparency = (H_s->n_bands == 4);
+ bool transparency = (H_s->n_bands == 4 || (Conf->Transp != NULL && Conf->Transp->n_transp == 2));
  unsigned int k; /* Due to OPENMP on Windows requiring signed int loop variables */
  int64_t srow, scol; /* Due to OPENMP on Windows requiring signed int loop variables */
  uint64_t n_bands = H_s->n_bands;