[gimp] plug-ins: fix incorrect loading of CMYK PSD images without layers.

[Jacob Boerema <jboerema src gnome org>]

commit b7518195b5d010e12aca684f60fd7002cdad5d28
Author: Jacob Boerema <jgboerema gmail com>
Date:   Wed Oct 27 19:17:05 2021 -0400

    plug-ins: fix incorrect loading of CMYK PSD images without layers.
    
    PSD images using CMYK as color mode and without layers didn't load
    correctly (wrong colors).
    When a PSD does not have any layers, CMYK color mode was not converted to
    RGB.
    Note that PSD color images that do have layers (e.g. CMYK and LAB) store
    the merged image as RGB!
    To do all this we added a conversion for CMYK PSD with 0 layers and added
    code to correctly determine whether an alpha channel exists.
    This also fixes the case where loading the merged image of a 16 bit per
    channel RGBA psd loads with the alpha channel opaque.

 plug-ins/file-psd/psd-load.c | 36 +++++++++++++++++++++++++++++++++---
 1 file changed, 33 insertions(+), 3 deletions(-)
---
diff --git a/plug-ins/file-psd/psd-load.c b/plug-ins/file-psd/psd-load.c
index 69d98dc04c..de24edcb01 100644
--- a/plug-ins/file-psd/psd-load.c
+++ b/plug-ins/file-psd/psd-load.c
@@ -2090,6 +2090,7 @@ add_merged_image (GimpImage     *image,
   gint                  offset;
   gint                  i;
   gboolean              alpha_visible;
+  gboolean              alpha_channel = FALSE;
   GeglBuffer           *buffer;
   GimpImageType         image_type;
   GimpRGB               alpha_rgb;
@@ -2100,6 +2101,14 @@ 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 ||
@@ -2126,6 +2135,11 @@ add_merged_image (GimpImage     *image,
 
   if (img_a->merged_image_only)
     {
+      if (! img_a->transparency && extra_channels > 0)
+        {
+          alpha_channel = TRUE;
+          base_channels += 1;
+        }
       extra_channels = 0;
       total_channels = base_channels;
     }
@@ -2226,7 +2240,8 @@ add_merged_image (GimpImage     *image,
   if (img_a->merged_image_only ||
       img_a->num_layers == 0)            /* Merged image - Photoshop 2 style */
     {
-      image_type = get_gimp_image_type (img_a->base_type, img_a->transparency);
+      image_type = get_gimp_image_type (img_a->base_type,
+                                        img_a->transparency || alpha_channel);
 
       layer_size = img_a->columns * img_a->rows;
       pixels = g_malloc (layer_size * base_channels * bps);
@@ -2251,15 +2266,30 @@ add_merged_image (GimpImage     *image,
 
       buffer = gimp_drawable_get_buffer (GIMP_DRAWABLE (layer));
       if (img_a->color_mode == PSD_CMYK)
-        img_a->color_mode = PSD_RGB;
+        {
+          guchar *dst0;
+
+          dst0 = g_malloc (base_channels * layer_size * sizeof(float));
+          psd_convert_cmyk_to_srgb ( img_a,
+                                     dst0, pixels,
+                                     img_a->columns, img_a->rows,
+                                     alpha_channel);
+          g_free (pixels);
+          pixels = dst0;
+       }
 
       gegl_buffer_set (buffer,
                        GEGL_RECTANGLE (0, 0,
                                        gegl_buffer_get_width (buffer),
                                        gegl_buffer_get_height (buffer)),
-                       0, get_layer_format (img_a, (base_channels % 2) == 0),
+                       0, get_layer_format (img_a,
+                                            img_a->transparency ||
+                                            alpha_channel),
                        pixels, GEGL_AUTO_ROWSTRIDE);
 
+      if (img_a->color_mode == PSD_CMYK)
+        img_a->color_mode = PSD_RGB;
+
       /* Merged image data is blended against white.  Unblend it. */
       if (img_a->transparency)
         {