Digital Camera Master

Now that you’ve narrowed down your price-pain threshold, let’s look at underlying technologies. The type of image sensor in your camera has great impact on the quality of the images you get. The two primary sensor types are CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor). CCD and CMOS differ in the ways they record and process light, but the basic layout and capture methods are similar.

CCD is the most common sensor in digicams and lower-pixel count dSLRs. It is also the less expensive of the two sensors. CMOS is used by many of the high-pixel count dSLRs from Canon, Nikon, and Kodak. Figure 9 compares the two types of sensors.

Figure 9. CCD and CMOS sensors differ in how the data is processed.

CCD and CMOS sensors are made up of photosites, each of which contains a photodiode to collect the light and convert it into electrons. The transfer cell collects the electrons and converts them into the digital values that make up the image. CMOS does more of the computational work at the photosite itself instead of making the transfer cell carry the load. The advantages and disadvantages to CCD and CMOS sensors are as follows:

• Image quality. In the beginning, the cameras that used CCD sensors had better noise-handling characteristics, which reduced the grain-like image degradation resulting from low light and high ISO speed ratings, than those using CMOS (see nearby “Noise” sidebar for more). When comparing sensors of the same size, the photodiodes on a CCD are larger and more sensitive to light, resulting in a cleaner image. However, the newest CMOS sensors have excellent built-in noise reduction that surpasses most CCD sensors. In fact, current CMOS-equipped cameras from Canon have some of the best noise-reducing characteristics of any camera available.