The difference between elements in a photograph. Contrast can include the difference between light and dark areas, or a marked difference in colors.
Compression
The compression of digital files in a format that requires less storage space. Compression techniques are distinguished from each other by whether they remove detail and color from the image. Lossless techniques compress image data without removing detail; lossy techniques compress images by removing some detail. Joint Photographic Experts Group (JPEG) is a lossy compression technique supported by JPEG, PDF, and PostScript language file formats. PowerShot digital cameras store their images in JPEG format, which provides the best results with continuous-tone images, such as photographs, when the size of the file is an important factor.
Complimentary color
If two colors, combined in the proper proportion form white light, then they are complimentary colors.
Compact Flash Card
A digital image storing mechanism that is increasing in popularity and thus functionality. Flash memory is a safe, highly reliable form of storage that doesn't need power to hold the images after they are saved. It won't erase the images unless the user chooses to do so.
CMYK
a.k.a. Cyan, Magenta, Yellow, BlacK. The color model in which all colors are described as combinations of these four colors. Most color printers, ink-jet, laser, dye-sublimation, thermal, and crayon printers use these as their printer colors. One of the biggest challenges of desktop publishing is color matching because the conversion from RGB to CMYK can cause color shifts - making it difficult to match the print with what is on your monitor.
CMY
Cyan, Magenta and Yellow. The three colors used to make all other colors. Like CMYK, CMY is used in printing to create the colors seen in a print.
CMOS
Complementary Metal Oxide Semiconductor. A type of semiconductor that has been, until the EOS D30, widely unavailable for digital cameras. CMOS semiconductors use two circuits, negative and positive polarity circuits. Because only one of the circuits can be on at once, CMOS chips are less energy consuming than other chips that utilize simply one type of transistor. This is a clear advantage of the CMOS sensor over the standard CCDs in use today.
Center-Weighted
A method of determining the correct exposure for a photograph which gives more importance to the light meter reading at the center of the frame than to the peripheral areas. This method is often criticized for being too limiting to the photographer. The PowerShot S10, S20 and S100 all utilize a 3-point focal system that frees you from having to keep your subject centered at all times.
Linear CCD
a.k.a. scanner-type CCD, these sensors are long and thin, and capture an image by recording a vast number of individual "exposures" while scanning across the picture frame. These are best suited for still subjects and continuous illumination.
Area CCD
A square or rectangular CCD that can capture an entire image at once, which is essential for dynamic subjects and flash photography.
CCD
Charge-coupled device. The image sensor that separates the spectrum of color into red, green and blue for digital processing by the camera. In digital cameras both Area and Linear CCDs are used. A CCD captures only black-and-white images. The image is passed through red, green and blue filters in order to capture color.
