16 - Device calibration

Summary

In conventional photography, from capturing an image on a color negative to getting a color print back from a photofinisher, most consumers do not have to bother with measuring light and color because the entire image chain (from film to reflection print) has been designed to reproduce good tone and color, and the uncontrolled variables left are taken care of by the automatic focus and exposure algorithms in the camera, and automatic color–density balance algorithms in the photofinishing printer. The conventional photographic system is a closed system and no user intervention is required. In electronic imaging, the situation is quite different. Digital cameras, film scanners, paper scanners, color monitors, and color printers are not manufactured to the same system specifications. Therefore, these imaging devices require careful calibration to ensure that they work together to reproduce good color images. Figure 16.1 shows a general block diagram for a color imaging application. The image data from an input device have to be calibrated so that they can be manipulated and processed according to the algorithm specifications. Similarly, the image processing algorithm outputs a digital image in a chosen color metric and that image has to be converted through an output calibration so that the desired color image can be reproduced by the output device.

Let us say, we have a nice color picture (reflection print) of our relatives and friends, and wewould like to produce more copies of the picture to send to each of them. We use a scanner to digitize the picture into a digital file which is then sent to a color printer for printing.