diff --git a/src/image.c b/src/image.c
index 683e922..342a355 100644
--- a/src/image.c
+++ b/src/image.c
@@ -104,22 +104,37 @@ static uint8_t rgb_to_2bpp(uint8_t r, uint8_t g, uint8_t b, size_t x, size_t y)
     return (slot & (0x8000 >> ((y & 3) << 2) >> (x & 3)))? to: from;
 }
 
+static inline uint8_t bitmap_read_channel(uint8_t *buf,
+                                          size_t x, size_t y, size_t stride,
+                                          int channels,
+                                          int channel) {
+    return buf[channels*stride*y + channels*x + channel];
+}
+
 static inline void bitmap_read(uint8_t *buf,
                                size_t x, size_t y, size_t stride,
                                uint8_t *r, uint8_t *g, uint8_t *b,
                                int channels) {
-    *r = buf[channels*stride*y + channels*x];
-    *g = buf[channels*stride*y + channels*x + 1];
-    *b = buf[channels*stride*y + channels*x + 2];
+    *r = bitmap_read_channel(buf, x, y, stride, channels, 0);
+    *r = bitmap_read_channel(buf, x, y, stride, channels, 1);
+    *r = bitmap_read_channel(buf, x, y, stride, channels, 2);
+}
+
+static inline void bitmap_write_channel(uint8_t *buf,
+                                        size_t x, size_t y, size_t stride,
+                                        int channels,
+                                        int channel,
+                                        uint8_t v) {
+    buf[channels*stride*y + channels*x + channel] = v;
 }
 
 static inline void bitmap_write(uint8_t *buf,
                                 size_t x, size_t y, size_t stride,
-                                uint8_t r, uint8_t g, uint8_t b,
-                                int channels) {
-    buf[channels*stride*y + channels*x]     = r;
-    buf[channels*stride*y + channels*x + 1] = g;
-    buf[channels*stride*y + channels*x + 2] = b;
+                                int channels,
+                                uint8_t r, uint8_t g, uint8_t b) {
+    bitmap_write_channel(buf, x, y, stride, channels, 0, r);
+    bitmap_write_channel(buf, x, y, stride, channels, 1, g);
+    bitmap_write_channel(buf, x, y, stride, channels, 2, b);
 }
 
 static inline size_t size_2bpp_tile(size_t width, size_t height) {
@@ -547,7 +562,8 @@ static void bitmap_copy(cammy_image *dest,
                          to->x + x,
                          to->y + y,
                          dest->width,
-                         r, g, b, channels_dest);
+                         channels_dest,
+                         r, g, b);
         }
     }
 }
@@ -614,10 +630,10 @@ static void tile_copy_to_bitmap(cammy_image *dest,
                          x,
                          y,
                          from->width,
+                         channels,
                          src->palette[c].r,
                          src->palette[c].g,
-                         src->palette[c].b,
-                         channels);
+                         src->palette[c].b);
         }
     }
 }