![]() For a comparison of 24 bit vs 8 bit color, view the following page (in 24 bit PNG and 8 bit GIF formats respectively) The color lookup table then specifies colors in the full 24 bit true-color representation but it is so small relative to a normal sized image that the space it takes up is negligible. Thus, each pixel only requires 8 bits (1/3 of the space) to represent it. Instead, each pixel is represented by a single number (for 8 bit images, a value from 0-255) which is an index into a color lookup table. Image formats such as GIF also, generally, do not directly specify colors in the manner shown above. Additionally, some image formats allow for a much smaller range of colors (example: GIF is an 8 bit format and allows for only 256 different colors to be present in any image). Most image formats, therefore, are compressed to shrink the size of the image. This, however, is a very simple way of representing an image and takes a very large amount of disk space. ![]() It is also shown as an enlarged image (in the GIF format since the PPM format shown can not be displayed by most web browsers) where each pixel is replicated as a 50×50 solid colored square. The following is a super-simple image definition (3×3 image in ascii PPM format- from upper left, black, medium red, full red, medium grey, medium green, full green, white, medium blue, full blue). In the right proportions, red, green, and blue can be combined to form black, white, 254 shades of grey, and a vast array of colors (16,777,216 colors total). ![]() The simplest representation of an image has each pixel specified by three 8 bit (24 bits total) color values (ranging from 0-255) defining the amount of red, green, and blue respectively in each pixel. Each pixel (picture element) has one or more numbers associated with it, specifying a color which the pixel should be displayed in. ![]() For example, a large bitmap image saved in the lossy JPEG format will have a smaller file size than the same bitmap image saved as a losslessly-compressed PNG file, which in turn will be smaller than that image saved as an uncompressed BMP file.A raster image file is a rectangular array of regularly sampled values, known as pixels. NOTE: There are many file formats used for raster graphics, some of which include image compression to reduce file size. Scaling one up requires creating new data between the existing pixels, which can result in an image that's either blurry or blocky. Shrinking one down requires the data from multiple pixels to be combined, causing fine details to be lost. Since raster graphics consist of a grid of pixels, resizing one to change its resolution will necessarily change the contents of those pixels. An image with 24 bits of color depth uses three times as much data but can use more than 16 million colors. An image with 8 bits of color depth can only display 256 colors. A raster graphic's file size also depends on its color depth - how many bits of data each pixel requires. For example, an image 640 pixels wide by 480 pixels tall consists of 307,200 pixels total, while a larger 3072 x 2048 image requires 6,291,456 pixels. A higher-resolution image has more pixels and thus requires more disk space to store. The first is a raster graphic's image size, also known as its resolution - the number of pixels it is wide by the number of pixels it is tall. The file size of a raster graphic depends on several variables. They are one of the two primary image types for computer graphics with vector graphics. Most images on the Internet and your computer are raster graphics. Raster graphics are computer graphics that consist of a grid of pixels, also known as a bitmap.
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