Image Sensors and Color
Different image sensors register red, green, and blue (RGB) light. Each receptor senses the brightness of the light for its particular color. Three receptors in your eye correspond to each of these colors. A digital picture is actually composed of tiny dots (pixels), but when you look at it your brain processes the information to form one multicolored image.
CCD Versus CMOS
Digital cameras use image sensors to capture pictures. There are two types of image sensors: CCD (charge-coupled device) and CMOS (complementary metal oxide semiconductor). Not long ago, the only image sensors used in cameras were CCDs.
Both types capture light in essentially the same manner, but they differ in the ways they are manufactured and how they process images. CCDs are created using a special manufacturing process that enables them to transport a charge across the chip without distortion. CMOS chips are made using the same processes as microprocessors.
The human eye has about six million cone cells that are sensitive to color. They see images in a way that is similar to an RGB digital photography image sensor system. In addition, there are 90 million rod cells, which see brightness but do not see color. These work in low light and essentially produce black and white images.
Image Sensor Differences
Because of differences in manufacturing, there are several differences between CCD and CMOS sensors. But what do these technical differences mean to you in practical terms? Here's how they stack up:
CCD sensors create high-quality, low-noise images. CMOS tend to be more susceptible to noise (small defects in the image).
The light sensitivity of a CMOS chip is lower.
CMOS sensors typically consume little power, while CCDs use a special process that consumes lots of power.
CMOS chips are less expensive to make than CCDs.
CCD sensors tend to have higher-quality pixels and a greater number of them.
Images Sensor Problems and Advantages
Because of these differences, CCDs are commonly used in cameras that create high-quality images with lots of pixels and superior light sensitivity. However, CCD chips have a problem with blooming, meaning they tend to produce undesired halos around very bright highlights. Blooming can occur when there is an area of concentrated light in your frame. It can happen in very bright daylight in studio light, or if there is a bright source of glare in your scene.
While CCDs have dominated the market, CMOS technology has kept developing. Popular camera maker Canon has used CMOS technology for several years in a number of its cameras. Expect more CMOS cameras in the future, with big names like Canon and Kodak leading the way.
For instance, if you're shooting a picture of the relatives gathered at the Thanksgiving table, the glowing candles on the table can cause blooming. The camera's CCD sensors will overload, then the charge from the overexposed pixels will seep into adjacent cells, causing a colored halo to form around bright or shiny objects, or causing random flashes of light. See the color pages for two night shots where the street lights cause blooming to occur.
CMOS cameras currently offer several advantages, including lower price tags and great battery life. Also, CMOS chips are better at capturing high-lights than CCDs, making them a better choice for shooting objects such as jewelry or capturing the glint of sunlight on the ocean.
