A raster image is a digital image represented by pixels, with formats including .gif, .jpg, and .bmp. The resolution determines the number of pixels per inch, affecting color gradation and image size. Vector images use mathematical formulas and are best for typography and line art.
A raster image, also called a bitmap, is a way to represent digital images. It can be created in a variety of formats, including the familiar .gif, .jpg, and .bmp. The image is represented in a series of bits of information which translate into pixels on the screen. These pixels form dots of color which create a finished overall image.
When a raster image is created, the screen image is converted to pixels. Each pixel is assigned a specific value that determines its color. This format uses the red, green, blue (RGB) color system. An RGB value of 0,0,0 would be black, and values go up to 256 for each color, allowing for the expression of a wide range of values. In photographs with subtle nuances, this can be extremely valuable.
When the image is viewed, the pixels usually dim visually for the user, who sees a photograph or drawing. When zoomed in, however, individual points of color become apparent. While this effect is sometimes a deliberate choice on the part of an artist, it is usually not desired. Depending on the resolution, some images can be enlarged to very large sizes, while others quickly become difficult to see. The smaller the resolution, the smaller the digital image file, so people who work with computer graphics need to strike a balance between resolution and image size.
Resolution refers to the number of pixels per inch (PPI) or dots per inch (DPI) in the image. The higher the resolution, the higher the number of pixels, allowing for greater color gradation that will translate better as the image is zoomed in. Of course, the more pixels there are, the more individual data points need to be stored. For high-quality photography, a high DPI is preferable because the images will appear more appealing to the viewer. For small images that don’t need to be enlarged, or when quality isn’t important, a low DPI can be used.
The alternative type is the vector image, which uses a mathematical formula to draw an image. A vector image defines the points and the paths that connect them to form a digital representation of the image. Because math can be easily scaled, this type can be scaled up but still have smooth edges. However, their use is limited and they are best suited for typography, line art and illustrations. A raster image usually remains the best choice for a shaded photograph or drawing.
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