Pixel size and well capacity
The electrons are held in each pixel and are converted into electrical charge which can be measured to show the amount of light that has fallen on each pixel. The maximum electrical charge possible is termed "full well capacity". The greater the full well capacity the greater the dynamic range, assuming other influencing factors such as noise and A/D converter quality are equal. As there is a limit to the depth to which pixels can be made, the full well capacity is often proportional to the frontal area of the light gathering element of the pixel.