do not convert channels

images/PNGReader.cpp

@@ -30,6 +30,7 @@ Error PNGReader::loadIntern(const char* path) {
 
     LodePNGState state;
     lodepng_state_init(&state);
+    state.decoder.color_convert = false;
     error = lodepng_decode(&data, &width, &height, &state, rawData, rawSize);
     if(error) {
         Error e = {"cannot decode file '"};