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A color image is a picture displayed in color by a computerized device on an attached or separate display screen. By contrast, black-and-white images and gray-scale images are pictures displayed only in black and white or in gray tones. A color image can exist in a variety of different file formats that determine how it is presented and stored. For color images to be displayed properly, the computerized device must possess or be attached to a display apparatus, such as a monitor, that is capable of showing the required colors. Changes in the file format and in the device used to display the image can cause subtle differences in the appearance of the image's colors.
Color image files contain information about the color of each of the image's pixels. The manner in which color information for each pixel is stored can be compared to coordinates in three or more dimensions. One common method of indicating a given color, for instance, involves stating a value for the "intensity" of red, green, and blue in a color image. The combination of these colors can be used to generate a broad spectrum of different colors, so specifying the particular combination of the three is often sufficient for indicating the exact color of a pixel. Another common coordinate-based color system is "HSL," or hue-saturation-lightness, in which different values for hue, saturation, and lightness are used to generate the necessary colors.
The quality of different color image formats can vary dramatically based on size, compression, and a variety of other factors. A certain amount of disk space is necessary for storing the color information of each pixel. A high-quality color image, then, usually has a large file size, as each pixel contains a substantial amount of color information. Small, low-quality images are sufficient for most purposes, but they might contain small irregularities and imperfections that suggest a small file size and limited image quality.
People use color images in many different settings. Most computer user interfaces are displayed in color and constantly require the generation of color images. It is almost impossible to browse the Internet without encountering a color image somewhere, whether in the form of advertisements or actual web content. Some jobs and research projects involve the development, processing, and study of high-quality color images. Such images often have very large file sizes, as subtle differences in the arrangements and densities of pixels of different colors can be quite important.