Hi, Yes, it works fine without const. I used const automatically because I don't write in my image but I don't think it changes something. So without seems to be better because it's not the correct way to deal with const inside gil. I don't know how we can declare a parameter to be a const view... For example a simple function that takes an image v and returns if it contains a pixel p: template<class MyGilConstView> bool f( const MyGilConstView& v, const MyGilConstView::value_type& p ); This function can't garantee that it doesn't modify the image v and the pixel p. I can create a const view at the begining of the function, to get this garantee, like this: typedef MyGilConstView::const_t MyGilReallyConstView; typedef MyGilReallyConstView::value_type MyGilReallyConstPixel; // as there is no const_t typedef in pixel type... MyGilReallyConstView cv = v; MyGilReallyConstPixel cp = p; Is it correct ? Is there a better way to do it ? Regards, Fabien PS: maybe a "typedef value_type pixel_t" inside the view class can be a good thing for readability ?