Screen Coordinates to UI Texture Coordinates

Hi, I'm having trouble from taking the screen coordinates of a UI element and using them to find the equivalent texture coordinates of an image behind.

I have the screen coordinates of a UI Rect Transform by just doing RectTransform.Position, and I have a RawImage below, which is showing a WebCamTexture, which is captured from my device camera.

In order to run GetPixel on the texture to get the colour underneath the UI element, I need the UV/Texture coords, but I have tried everything to convert between Screen to Texture but I've had no luck. Just wondering the best way to do so.

Thanks - let me know if you need to see any code.