Visual Inspection of CCD Images

Charge Transfer Inefficiency (CTI)

https://www.stsci.edu/hst/instrumentation/stis/data-analysis-and-software-tools/pixel-based-cti

Dark Current

when it is low, it's a poisson (the first peak corresponding to zero electron, n_th peak correspond to (n-1) electron)

but when it is high, it's possion with high expectation value -> like an gaussian

(so if you see something doesn't look like a gaussian, e.g. very high first peak, something is not going right -> we are losing charge in some pixels)

Crosstalk

when a high energy event happens in one CCD, on the CCD paired with it (A-D; B-C), at the same location there will also be some signal of the shape (usually lower than pur noise)