3 files changed, 63 insertions, 1 deletions
diff --git a/lib/libpnm3.c b/lib/libpnm3.c
index 80ccadfa..c7951546 100644
--- a/lib/libpnm3.c
+++ b/lib/libpnm3.c
@@ -345,3 +345,45 @@ xeltopixel(xel const inputxel) {
                PNM_GET1(inputxel), PNM_GET1(inputxel), PNM_GET1(inputxel));
     return outputpixel;
 }
+
+
+
+xel
+pnm_parsecolorxel(const char * const colorName,
+                  xelval       const maxval,
+                  int          const format) {
+
+    pixel const bgColor = ppm_parsecolor(colorName, maxval);
+
+    xel retval;
+
+    switch(PNM_FORMAT_TYPE(format)) {
+    case PPM_TYPE:
+        PNM_ASSIGN(retval,
+                   PPM_GETR(bgColor), PPM_GETG(bgColor), PPM_GETB(bgColor));
+        break;
+    case PGM_TYPE:
+        if (PPM_ISGRAY(bgColor))
+            PNM_ASSIGN1(retval, PPM_GETB(bgColor));
+        else
+            pm_error("Non-gray color '%s' specified for a "
+                     "grayscale (PGM) image",
+                     colorName);
+                   break;
+    case PBM_TYPE:
+        if (PPM_EQUAL(bgColor, ppm_whitepixel(maxval)))
+            PNM_ASSIGN1(retval, maxval);
+        else if (PPM_EQUAL(bgColor, ppm_blackpixel()))
+            PNM_ASSIGN1(retval, 0);
+        else
+            pm_error ("Color '%s', which is neither black nor white, "
+                      "specified for a black and white (PBM) image",
+                      colorName);
+        break;
+    default:
+        pm_error("Invalid format code %d passed to pnm_parsecolor()",
+                 format);
+    }
+    
+    return retval;
+}
diff --git a/lib/pnm.h b/lib/pnm.h
index f4469bf5..354eacf9 100644
--- a/lib/pnm.h
+++ b/lib/pnm.h
@@ -126,6 +126,11 @@ pnm_promoteformatrow(xel* xelrow, int cols, xelval maxval, int format,
 pixel
 xeltopixel(xel const inputxel);
 
+xel
+pnm_parsecolorxel(const char * const colorName,
+                  xelval       const maxval,
+                  int          const format);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/ppm.h b/lib/ppm.h
index 622d3e09..7f7d6446 100644
--- a/lib/ppm.h
+++ b/lib/ppm.h
@@ -58,7 +58,22 @@ typedef struct {
   ((f) == PPM_FORMAT || (f) == RPPM_FORMAT ? PPM_TYPE : PGM_FORMAT_TYPE(f))
 
 
-/* Declarations of routines. */
+static __inline__ pixel
+ppm_whitepixel(pixval maxval) {
+
+    pixel retval;
+    PPM_ASSIGN(retval, maxval, maxval, maxval);
+
+    return retval;
+}
+
+static __inline__ pixel
+ppm_blackpixel(void) {
+
+    pixel const retval = {0, 0, 0};
+
+    return retval;
+}
 
 void ppm_init(int * argcP, char* argv[]);