From e6ad3ad0cd0406702ca7acba528bc6a414183d70 Mon Sep 17 00:00:00 2001
From: Alx Sa <cmyk.student@gmail.com>
Date: Sun, 1 Dec 2024 16:18:20 +0000
Subject: [PATCH] plug-ins: Add support for importing CMYK PAM files

While not an "official" tupl type for PAM files, software such as
mutools can export CMYK PAM files. This patch adds support
for loading such images.
Note that PAM files do not include color profile information. In
the future, we might add an option to convert using a pre-defined
color profile for this and other formats like EPS.
---
 plug-ins/common/file-pnm.c | 40 ++++++++++++++++++++++++++------------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/plug-ins/common/file-pnm.c b/plug-ins/common/file-pnm.c
index 397eee5b32..32a33a4f35 100644
--- a/plug-ins/common/file-pnm.c
+++ b/plug-ins/common/file-pnm.c
@@ -93,6 +93,7 @@ struct _PNMInfo
   gboolean      float_format;   /* Whether it is a floating point format */
   gint          maxval;         /* For integer format image files, the max value
                                  * which we need to normalize to */
+  gchar        *tupltype;       /* Pixel color model */
   gfloat        scale_factor;   /* PFM files have a scale factor */
   gint          np;             /* Number of image planes (0 for pbm) */
   gboolean      asciibody;      /* 1 if ascii body, 0 if raw body */
@@ -694,6 +695,8 @@ load_image (GFile   *file,
   /* allocate the necessary structures */
   pnminfo = g_new (PNMInfo, 1);
 
+  pnminfo->tupltype = NULL;
+
   scan = NULL;
   /* set error handling */
   if (setjmp (pnminfo->jmpbuf))
@@ -852,6 +855,8 @@ load_image (GFile   *file,
   pnmscanner_destroy (scan);
 
   g_object_unref (buffer);
+  if (pnminfo->tupltype)
+    g_free (pnminfo->tupltype);
   g_free (pnminfo);
   g_object_unref (input);
 
@@ -895,16 +900,22 @@ process_pam_header (PNMScanner *scan,
 
           /* PAM files may have custom tupltypes;
            * however, these are the only 'officially' defined
-           * ones */
+           * ones (plus CMYK since this tupltype exists in the
+           * wild. */
           if (strcmp (buf, "BLACKANDWHITE")       &&
               strcmp (buf, "BLACKANDWHITE_ALPHA") &&
               strcmp (buf, "GRAYSCALE")           &&
               strcmp (buf, "GRAYSCALE_ALPHA")     &&
               strcmp (buf, "RGB")                 &&
-              strcmp (buf, "RGB_ALPHA"))
+              strcmp (buf, "RGB_ALPHA")           &&
+              strcmp (buf, "CMYK"))
             {
               is_unsupported_tupltype = TRUE;
             }
+
+          if (! strcmp (buf, "CMYK"))
+            pnminfo->tupltype = g_strdup ("CMYK");
+
         }
       else if (! strcmp (buf, "ENDHDR"))
         {
@@ -1046,6 +1057,7 @@ pnm_load_raw (PNMScanner *scan,
               GeglBuffer *buffer)
 {
   GInputStream *input;
+  const Babl   *format = NULL;
   gint          bpc;
   guchar       *data, *d;
   gushort      *s;
@@ -1117,9 +1129,13 @@ pnm_load_raw (PNMScanner *scan,
             }
         }
 
+      if (info->tupltype != NULL && ! strcmp (info->tupltype, "CMYK"))
+        format = (bpc == 1) ? babl_format ("CMYK u8") :
+                              babl_format ("CMYK u16");
+
       gegl_buffer_set (buffer,
                        GEGL_RECTANGLE (0, y, info->xres, scanlines), 0,
-                       NULL, data, GEGL_AUTO_ROWSTRIDE);
+                       format, data, GEGL_AUTO_ROWSTRIDE);
 
       gimp_progress_update ((double) y / (double) info->yres);
     }
@@ -1280,15 +1296,15 @@ output_write (GOutputStream *output,
 }
 
 static void
-create_pam_header (const gchar   **header_string,
-                   PNMRowInfo     *rowinfo,
-                   PNMExportrowFunc *saverow,
-                   GimpImageType   drawable_type,
-                   GeglBuffer     *buffer,
-                   const Babl    **format,
-                   gint           *rowbufsize,
-                   gint           *np,
-                   gchar          *comment)
+create_pam_header (const gchar      **header_string,
+                   PNMRowInfo        *rowinfo,
+                   PNMExportrowFunc  *saverow,
+                   GimpImageType      drawable_type,
+                   GeglBuffer        *buffer,
+                   const Babl       **format,
+                   gint              *rowbufsize,
+                   gint              *np,
+                   gchar             *comment)
 {
   gint   maxval   = 255;
   gint   xres     = gegl_buffer_get_width (buffer);