high speed film to digital conversion the remainder of this description will involve 2 dimensional arrays each cell of a 2 dimensional ccd array can be modeled as shown in fig3 a photosensitive diode generates a current when light energy impinges on it this current is stored on a capacitor as charge the voltage on the capacitor is approximately proportional to the intensity of the light hitting it 0018 fig4 shows how the rectangular array of ccd cells shown in fig3 is multiplexed onto a single video line consider a logical 1 in the leftmost storage element of the horizontal shift register and in the top storage element of the vertical shift register transistor a is turned on and the voltage on the capacitor in the upper left corner becomes the output on the video line at the end of a pixel period the logical 1 is moved to the second position in the horizontal shift register with the first position being set to logical zero at this point the voltage on the second capacitor in the first row of the array becomes the output on the video line this process continues until the last cell in the first row is selected at the end of this pixel the logical 1 in the vertical shift register is moved down one position and the logical 1 in the horizontal shift register moves back to the left most storage element this process.