[gimp] plug-ins: improve loading of PSD merged images with alpha channel

[Jacob Boerema <jboerema src gnome org>]

commit f7e327ca058dfe40444409a12c448a03a07eaa0c
Author: Jacob Boerema <jgboerema gmail com>
Date:   Mon Nov 8 22:36:49 2021 -0500

    plug-ins: improve loading of PSD merged images with alpha channel
    
    Handling of PSD merged images with alpha channel but where merged
    transparency is not used is complicated.
    We check the alpha_names resource for the presence of 'Transparency'. If
    that is present, assume we have an alpha channel.
    In case of a CMYKA PSD with layers the merged image actually is RGB with
    the first three channels representing RGB and the Alpha in the fifth
    channel. In this case we move the alpha data to the forth channel so
    we can handle it as RGBA.

 plug-ins/file-psd/psd-image-res-load.c |  6 +--
 plug-ins/file-psd/psd-load.c           | 90 +++++++++++++++++++++++++---------
 2 files changed, 69 insertions(+), 27 deletions(-)
---
diff --git a/plug-ins/file-psd/psd-image-res-load.c b/plug-ins/file-psd/psd-image-res-load.c
index 8acfc8583e..86a1f0f660 100644
--- a/plug-ins/file-psd/psd-image-res-load.c
+++ b/plug-ins/file-psd/psd-image-res-load.c
@@ -341,8 +341,7 @@ load_image_resource (PSDimageres  *res_a,
             break;
 
           case PSD_ALPHA_NAMES:
-            if (! img_a->merged_image_only)
-              load_resource_1006 (res_a, image, img_a, input, error);
+            load_resource_1006 (res_a, image, img_a, input, error);
             break;
 
           case PSD_DISPLAY_INFO:
@@ -383,8 +382,7 @@ load_image_resource (PSDimageres  *res_a,
             break;
 
           case PSD_ALPHA_NAMES_UNI:
-            if (! img_a->merged_image_only)
-              load_resource_1045 (res_a, image, img_a, input, error);
+            load_resource_1045 (res_a, image, img_a, input, error);
             break;
 
           case PSD_IDX_COL_TAB_CNT:
diff --git a/plug-ins/file-psd/psd-load.c b/plug-ins/file-psd/psd-load.c
index 78b2e1c5cc..c39e1e747b 100644
--- a/plug-ins/file-psd/psd-load.c
+++ b/plug-ins/file-psd/psd-load.c
@@ -206,9 +206,6 @@ load_image (GFile        *file,
           g_warning ("No error message but loading layer failed. This should not happen!");
           goto load_error;
         }
-      else
-        /* Only a merged image present, no layers. */
-        img_a.merged_image_only = TRUE;
     }
   gimp_progress_update (0.4);
 
@@ -2142,6 +2139,7 @@ add_merged_image (GimpImage     *image,
   gint                  i;
   gboolean              alpha_visible;
   gboolean              alpha_channel = FALSE;
+  gboolean              original_mode_CMYK = FALSE;
   GeglBuffer           *buffer;
   GimpImageType         image_type;
   GimpRGB               alpha_rgb;
@@ -2152,14 +2150,6 @@ add_merged_image (GimpImage     *image,
   if (bps == 0)
     bps++;
 
-  if (img_a->num_layers > 0 && img_a->color_mode == PSD_CMYK)
-    {
-      /* In this case there is no conversion. Merged image is RGB. */
-      img_a->color_mode = PSD_RGB;
-      if (! img_a->transparency)
-        total_channels--;
-    }
-
   if ((img_a->color_mode == PSD_BITMAP ||
        img_a->color_mode == PSD_MULTICHANNEL ||
        img_a->color_mode == PSD_GRAYSCALE ||
@@ -2180,21 +2170,43 @@ add_merged_image (GimpImage     *image,
     {
       extra_channels = total_channels - 4;
     }
-  if (img_a->transparency && extra_channels > 0)
-    extra_channels--;
-  base_channels = total_channels - extra_channels;
 
-  if (img_a->merged_image_only)
+  if (img_a->merged_image_only &&
+      img_a->color_mode == PSD_CMYK &&
+      img_a->num_layers > 0)
+    {
+      /* In this case there is no conversion. Merged image is RGB. */
+      img_a->color_mode = PSD_RGB;
+      original_mode_CMYK = TRUE;
+      if (! img_a->transparency)
+        {
+          total_channels--;
+        }
+    }
+
+  if (extra_channels > 0)
     {
-      if (! img_a->transparency && extra_channels > 0)
+      if (img_a->transparency)
+        {
+          extra_channels--;
+        }
+      else if (img_a->alpha_names)
         {
-          alpha_channel = TRUE;
-          base_channels += 1;
+          gchar *alpha_name;
+
+          /* If first alpha_name is Transparency consider it the alpha channel. */
+          alpha_name = g_ptr_array_index (img_a->alpha_names, 0);
+          if (! g_strcmp0 (alpha_name, "Transparency"))
+            {
+              alpha_channel = TRUE;
+              base_channels += 1;
+              extra_channels--;
+              IFDBG(3) g_debug ("Merged image alpha channel present.");
+            }
         }
-      extra_channels = 0;
-      total_channels = base_channels;
     }
 
+  base_channels = total_channels - extra_channels;
   /* ----- Read merged image & extra channel pixel data ----- */
   if (img_a->merged_image_only ||
       img_a->num_layers == 0   ||
@@ -2325,7 +2337,7 @@ add_merged_image (GimpImage     *image,
           psd_convert_cmyk_to_srgb (img_a,
                                     dst0, pixels,
                                     img_a->columns, img_a->rows,
-                                    alpha_channel);
+                                    img_a->transparency || alpha_channel);
           g_free (pixels);
           pixels = dst0;
        }
@@ -2337,10 +2349,41 @@ add_merged_image (GimpImage     *image,
           psd_convert_lab_to_srgb (img_a,
                                    dst0, pixels,
                                    img_a->columns, img_a->rows,
-                                   img_a->transparency);
+                                   img_a->transparency || alpha_channel);
           g_free (pixels);
           pixels = dst0;
-       }
+        }
+      else if (original_mode_CMYK && img_a->transparency)
+        {
+          gint    irow;
+          guchar *dst0, *dst;
+          guchar *data;
+
+          dst0 = g_malloc (base_channels * layer_size * sizeof(guchar));
+          dst  = dst0;
+          data = pixels;
+
+          /* CMYKA layers: 5 channels but merged image is RGBA
+           * with RGB in the first 3 layers and A in 5th layer.
+           * Move A to 4th layer. */
+          for (irow = 0; irow < img_a->rows; irow++)
+            {
+              gint icol;
+
+              for (icol = 0; icol < img_a->columns; icol++)
+                {
+                  dst[0] = data[0];
+                  dst[1] = data[1];
+                  dst[2] = data[2];
+                  dst[3] = data[4];
+
+                  dst  += 4;
+                  data += 5;
+                }
+            }
+          g_free (pixels);
+          pixels = dst0;
+        }
 
       gegl_buffer_set (buffer,
                        GEGL_RECTANGLE (0, 0,
@@ -2359,6 +2402,7 @@ add_merged_image (GimpImage     *image,
         {
           GeglBufferIterator *iter;
 
+          IFDBG(4) g_debug ("Unblend merged transparency");
           iter = gegl_buffer_iterator_new (buffer, NULL, 0,
                                            babl_format ("R'G'B'A float"),
                                            GEGL_ACCESS_READWRITE,