This can be a real troublemaker, since it can cause image artifacts. In some instances, a pixel drop out looks like black spots on the screen, either stationary or moving around. Several things can cause pixel drop out, such as the ADC not digitizing the video correctly. Also, the timing between the ADC and the frame buffer might not be correct, causing the wrong number to be stored in the buffer. For that matter, the timing anywhere in the video stream might cause a pixel drop out.