--- a/src/libgfx.h	Fri Aug 18 14:08:08 2017 +0300
+++ b/src/libgfx.h	Fri Aug 18 15:20:44 2017 +0300
@@ -46,13 +46,19 @@
 };
 
 
-// Bitmapped image struct (can be one of types specified by DM_IFMT_*)
+// Bitmapped image struct 
 typedef struct
 {
-    int width, height, pitch;
-    BOOL constpal;
-    int ncolors, ctransp;
-    DMColor *pal;
+    int format;     // one of types specified by DM_IFMT_*
+    int width, height;
+    int pitch;      // bytes per scanline
+    int bpp;        // bits per pixel
+
+    int ncolors;    // number of colors in palette, if any
+    int ctransp;    // transparency color index
+    BOOL constpal;  // is the palette a const?
+    DMColor *pal;   // pointer to palette struct, NULL if no palette
+
     size_t size;
     Uint8 *data;
 } DMImage;
@@ -89,9 +95,9 @@
 extern int dmGFXErrorMode;
 
 
-DMImage * dmImageAlloc(int width, int height);
+DMImage * dmImageAlloc(const int width, const int height, const int format, const int bpp);
 void      dmImageFree(DMImage *img);
-int       dmImageGetBytesPerPixel(int format);
+int       dmImageGetBytesPerPixel(const int format);
 int       dmImageProbeGeneric(const Uint8 *buf, const size_t len, DMImageFormat **fmt, int *index);
 
 BOOL dmCompareColor(const DMColor *c1, const DMColor *c2, BOOL alpha);