diff --git a/include/libopencm3/stm32/f4/ltdc.h b/include/libopencm3/stm32/f4/ltdc.h
index 5e49e28b..2a1812b6 100644
--- a/include/libopencm3/stm32/f4/ltdc.h
+++ b/include/libopencm3/stm32/f4/ltdc.h
@@ -168,6 +168,16 @@ void ltdc_setup_windowing(
 		uint16_t active_width,  uint16_t active_height
 );
 
+/**
+ * color conversion helper function
+ * (simulate the ltdc color conversion)
+ */
+
+#define ltdc_get_rgb888_from_rgb565(rgb888) ( \
+	((((rgb888) & 0xF800) >> (11-8))/31)<<16    \
+  | ((((rgb888) & 0x07E0) << ( 8-5))/63)<<8     \
+  | ((((rgb888) & 0x001F) << ( 8-0))/31)<<0     \
+)
 
 
 #endif /* LIBOPENCM3_STM32_F4_LTDC_H_ */