Calculation of absolute image intensities

I believe the calculation of absolute image intensities is off.

In "ray_tracing_backend.py" "base_image_for_detector" (line 202-207) the pixel intensities without absorption are calculated as I_0 = 1/ray_length²

I think the area or solid angle of a single pixels needs to be taken into account for the base image.

Either as:

I_0= 1/ray_length² x solidAngle(pixel)

or as:

I_0= 1/(4 x pi x ray_length²) x area(pixel)

@54E81AF7EAB270E9 @2F810571D6CB9F0E : Please comment