First and second images of a semiconductor die or portion thereof are generated. Generating each image includes performing a respective instance of time-domain integration (TDI) along a plurality of pixel columns in an imaging sensor, while illuminating the imaging sensor with light scattered from the semiconductor die or portion thereof. The plurality of pixel columns comprises pairs of pixel columns in which the pixel columns are separated by respective channel stops. While performing a first instance of TDI to generate the first image, a first bias is applied to electrically conductive contacts of the channel stops. While performing a second instance of TDI to generate the second image, a second bias is applied to the electrically conductive contacts of the channel stops. Defects in the semiconductor die or portion thereof are identified using the first and second images.