Photometric measurements
	• Isophotal magnitudes: pixel values are integrated within a given isophote § Fast and simple § Consistent with the idea that sources are uniquely defined by a list of pixels § Reasonably robust to contamination by close neighbours § Fairly efficient in terms of signal-to-noise § Strongly biased against faint and low-surface brightness sources § Unless the limiting isophote is very low, or a Monte-Carlo model is available for comparison, should be used for rough magnitude estimates only