Amplifier gain correction diagram. We label each one of the four 507 × 507 pixel sections of the WFC3 IR detector as A, B, C, D (see figure). We represent with a blue transparent gradient the weights (bluer represents higher weights) applied to the corresponding pixels of each region, labelled accordingly. The white regions in the background are masked pixels, either because they are part of a light source or are affected by persistence. We do not include those pixels in the amplifier gain correction estimation.