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A 2-bit indexed color image. The color of each pixel is represented by a number; each number (the index) corresponds to a color in the color table (the palette).. In computing, indexed color is a technique to manage digital images' colors in a limited fashion, in order to save computer memory and file storage, while speeding up display refresh and file transfers.
The number of channels depends on whether the image is grayscale or color and whether it has an alpha channel. PNG allows the following combinations of channels, called the color type. A demonstration of the color depth in a PNG file, in bits per channel. Left: 8 bits; Right: 16 bits. Note the artifacts, adjusted contrast for clarity.
8-bit color, with three bits of red, three bits of green, and two bits of blue. In order to turn a true color 24-bit image into an 8-bit image, the image must go through a process called color quantization. Color quantization is the process of creating a color map for a less color dense image from a more dense image. [2]
WebP is a raster graphics file format developed by Google intended as a replacement for JPEG, PNG, and GIF file formats. It supports both lossy and lossless compression, [8] as well as animation and alpha transparency.
The typical range of intensity values for each color, 0–255, is based on taking a binary number with 32 bits and breaking it up into four bytes of 8 bits each. 8 bits can hold a value from 0 to 255. The fourth byte is used to specify the "alpha", or the opacity, of the color. Opacity comes into play when layers with different colors are stacked.
Use the lowest bit depth that can handle all colours in your image, although some image editing programs cannot create 2-bit colour images. If you are converting an image with many colours (perhaps because somebody saved the original as a JPEG, avoid this ) to a PNG, you may want to reduce the number of colours at the same time; see Wikipedia ...
For example, the above 192×128 PNG (Portable Network Graphics) image has a file size of 166 bytes. When converted to a 192×128 PPM image, the file size is 73,848 bytes. Filesize reduction factor 100 or so when converting to png is typical if the image is a line drawing; if the image is a photo, it is best converted to jpeg, which yields a ...
In addition, transparency is often an "extra" for a graphics format, and some graphics programs will ignore the transparency. Animated PNG 8-bit transparency. Raster file formats that support transparency include GIF, PNG, BMP, TIFF, TGA and JPEG 2000, through either a transparent color or an alpha channel.