Isophotal photometry
= Isophotal photometry
<isophotal photometry> measures an extended source's <radiative flux> inside a contour of fixed <surface brightness>. It misses light outside that contour. The fraction lost depends on the intrinsic brightness profile, convolution with the <point spread function>, <sky background> estimation and the chosen threshold. A per-pixel threshold is not a fundamental limit on fitting or averaging many faint pixels together.