Raster images are usually the result of the digitizing of continuous-tone images, such as photographs or original painted or drawn artwork. Raster images are comprised of a grid of squares, which are called pixels. Pixel is short for PICture Element and is the smallest component of a digital image. If you’ve ever looked at a bathroom wall made up of those small square tiles reminiscent of the ’40s, you’re familiar with what a grid of pixels looks like: Each pixel lives in a specific location on that grid and contains a single color. When you edit a bitmap image, you are editing one or more pixels rather than an object-oriented shape.
Although it doesn’t seem like it when you’re viewing an image that fits inside your computer screen, your entire image can be broken down into a grid of square pixels. That means the elliptical shapes of my beanie also have to fit within this system of squares. But how do you fit a round peg in a square hole? By faking it. Unlike the true mathematical curve possible when drawing vector shapes, raster images must try to approximate a curve by mimicking the overall shape with square pixels.
Fortunately, the mimicry the pixels have to do is indecipherable with high-resolution images viewed at a reasonable distance. But when you zoom in, you can see that a curve in an image (like the curve of my beanie) is indeed comprised of square pixels. Raster graphics work great for photorealistic or painterly images where subtle gradations of color are necessary. On the downside, because they contain a fixed number of pixels, raster graphics can suffer a degradation of quality when they’re enlarged or otherwise transformed. They are also large in file size.
Although it doesn’t seem like it when you’re viewing an image that fits inside your computer screen, your entire image can be broken down into a grid of square pixels. That means the elliptical shapes of my beanie also have to fit within this system of squares. But how do you fit a round peg in a square hole? By faking it. Unlike the true mathematical curve possible when drawing vector shapes, raster images must try to approximate a curve by mimicking the overall shape with square pixels.
Fortunately, the mimicry the pixels have to do is indecipherable with high-resolution images viewed at a reasonable distance. But when you zoom in, you can see that a curve in an image (like the curve of my beanie) is indeed comprised of square pixels. Raster graphics work great for photorealistic or painterly images where subtle gradations of color are necessary. On the downside, because they contain a fixed number of pixels, raster graphics can suffer a degradation of quality when they’re enlarged or otherwise transformed. They are also large in file size.
Bitmap images are resolution dependent. Because they contain a fixed number of pixels, the resolution of the device they are being printed to is only one of two factors that influence the quality of the image. The quality of the output also depends heavily on the resolution of the image. For example, an image with 72 dots per inch (dpi) doesn’t look any better printed on a 600 dpi printer than it does on a 1200 dpi printer. Likewise, a 300 dpi image doesn’t look as good printed on an old 72 dpi dot matrix printer as it does on a 1200 dpi printer.
Raster images in Photoshop
![Raster images in Photoshop]()
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