Merge branch 'fix-18187'

* fix-18187:
  Treat data with 2 samples per pixel as monochrome
  Actually we can read TIFF files with arbitrary number of samples per pixel

src/imageio/imageio_tiff.c

@@ -99,7 +99,7 @@ static inline int _read_chunky_8(tiff_t *t)
       /* set rgb to first sample from scanline */
       out[0] = ((float)in[0]) * (1.0f / 255.0f);
 
-      if(t->spp == 1)
+      if(t->spp < 3)  // mono, maybe plus alpha channel
       {
         out[1] = out[2] = out[0];
       }
@@ -130,7 +130,7 @@ static inline int _read_chunky_16(tiff_t *t)
     {
       out[0] = ((float)in[0]) * (1.0f / 65535.0f);
 
-      if(t->spp == 1)
+      if(t->spp < 3)  // mono, maybe plus alpha channel
       {
         out[1] = out[2] = out[0];
       }
@@ -165,7 +165,7 @@ static inline int _read_chunky_h(tiff_t *t)
       out[0] = _half_to_float(in[0]);
 #endif
 
-      if(t->spp == 1)
+      if(t->spp < 3)  // mono, maybe plus alpha channel
       {
         out[1] = out[2] = out[0];
       }
@@ -201,7 +201,7 @@ static inline int _read_chunky_f(tiff_t *t)
     {
       out[0] = in[0];
 
-      if(t->spp == 1)
+      if(t->spp < 3)  // mono, maybe plus alpha channel
       {
         out[1] = out[2] = out[0];
       }
@@ -237,7 +237,7 @@ static inline int _read_chunky_8_Lab(tiff_t *t, uint16_t photometric)
     {
       out[0] = ((float)in[0]) * (100.0f/255.0f);
 
-      if(t->spp == 1)
+      if(t->spp < 3)  // mono, maybe plus alpha channel
       {
         out[1] = out[2] = 0;
       }
@@ -293,7 +293,7 @@ static inline int _read_chunky_16_Lab(tiff_t *t, uint16_t photometric)
     {
       out[0] = ((float)in[0]) * (100.0f/range);
 
-      if(t->spp == 1)
+      if(t->spp < 3)  // mono, maybe plus alpha channel
       {
         out[1] = out[2] = 0;
       }
@@ -411,13 +411,6 @@ dt_imageio_retval_t dt_imageio_open_tiff(dt_image_t *img, const char *filename,
     return DT_IMAGEIO_UNSUPPORTED_FEATURE;
   }
 
-  /* we only support 1, 3 or 4 samples per pixel */
-  if(t.spp != 1 && t.spp != 3 && t.spp != 4)
-  {
-    TIFFClose(t.tiff);
-    return DT_IMAGEIO_UNSUPPORTED_FEATURE;
-  }
-
   /* don't depend on planar config if spp == 1 */
   if(t.spp > 1 && config != PLANARCONFIG_CONTIG)
   {