diff --git a/src/test.c b/src/test.c
index 390aad7..ff6be18 100644
--- a/src/test.c
+++ b/src/test.c
@@ -108,8 +108,12 @@ static void image_copy(cammy_sram_frame *frame, uint8_t *buf) {
                     g = buf[4*CAMMY_SRAM_PHOTO_WIDTH*y+4*x+1],
                     b = buf[4*CAMMY_SRAM_PHOTO_WIDTH*y+4*x+2];
 
-            uint8_t  avg  = (uint8_t)(((float)r + (float)g + (float)b) / 3);
-            uint32_t slot = bayer_matrix[avg];
+            uint8_t gray = (uint8_t)
+                ((0.2126 * (float)r)
+               + (0.7152 * (float)g)
+               + (0.0722 * (float)b));
+
+            uint32_t slot = bayer_matrix[gray];
             uint32_t from = (slot & 0x03000000) >> 24;
             uint32_t to   = (slot & 0x00030000) >> 16;
             uint8_t  value;