diff --git a/main/lib/image/gb.image.h b/main/lib/image/gb.image.h
index 7fe1735bc..caf2095af 100644
--- a/main/lib/image/gb.image.h
+++ b/main/lib/image/gb.image.h
@@ -158,6 +158,8 @@ typedef
 		const char *(*FormatToString)(int format);
 		// Return the luminance of a color
 		int (*GetLuminance)(GB_COLOR col);
+		// Invert an image, eventually preserving the color hue.
+		void (*Invert)(GB_IMG *img, bool keep_hue);
 		}
 	IMAGE_INTERFACE;
 
diff --git a/main/lib/image/main.c b/main/lib/image/main.c
index 597924514..6074a4a11 100644
--- a/main/lib/image/main.c
+++ b/main/lib/image/main.c
@@ -70,6 +70,7 @@ void *GB_IMAGE_1[] EXPORT =
 	(void *)COLOR_darker,
 	(void *)IMAGE_format_to_string,
 	(void *)COLOR_get_luminance,
+	(void *)IMAGE_invert,
   NULL
 };