Vignetting profile and falloff.

[SteveBz]

Hi Guys,

I've written a bit of code to subtract light pollution from an image.  Obviously, because of vignetting, the amount of light pollution varies across the image, being weakest at the four corners and strongest in the centre.  Am I right in thinking that the image is more or less constant brightness across a disc at the centre of the image, and then falls off linearly to the corners?

Of course the sensor may not be exactly centred, but if I could do some sort of calculation to ascertain the centre of the disk, maybe like one of the focussing algorithms like Half Flux Radius or something, maybe I could approximate the centre (or maybe I have to point and click to tell the program where it is), is there any algorithm that will tell me the size of the disk before the brightness of the image starts to fall off?  And then of course, how fast does it fall off?

Thanks,

Steve.

[michael8554]

Hi Steve,

Rather than theorise I would measure the rgb values from the middle to the corners of a flat taken with your setup.

Michael