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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.
A binary image is a digital image that consists of pixels that can have one of exactly two colors, usually black and white. Each pixel is stored as a single bit — i.e. either a 0 or 1. A binary image can be stored in memory as a bitmap : a packed array of bits.
Like any resampling operation, changing image size and bit depth are lossy in all cases of downsampling, such as 30-bit to 24-bit or 24-bit to 8-bit palette-based images. While increasing bit depth is usually lossless, increasing image size can introduce aliasing or other undesired artifacts.
The advantage over 8-bit or 16-bit integers is that the increased dynamic range allows for more detail to be preserved in highlights and shadows for images, and avoids gamma correction. The advantage over 32-bit single-precision floating point is that it requires half the storage and bandwidth (at the expense of precision and range). [5]
JPEG XT uses an extensible file format based on JFIF. Extension layers are used to modify the JPEG 8-bit base layer and restore the high-resolution image. Existing software is forward compatible and can read the JPEG XT binary stream, though it would only decode the base 8-bit layer. [79]
The 8-bit per pixel (8bpp) format supports 256 distinct colors and stores 1 pixel per 1 byte. Each byte is an index into a table of up to 256 colors. The 16-bit per pixel (16bpp) format supports 65536 distinct colors and stores 1 pixel per 2-byte WORD. Each WORD can define the alpha, red, green and blue samples of the pixel.
For example, graphically simple images (i.e. images with large continuous regions like line art or animation sequences) may be losslessly compressed into a GIF or PNG format and result in a smaller file size than a lossy JPEG format. For example, a 640 × 480 pixel image with 24-bit color would occupy almost a megabyte of space:
The P4 binary format of the same image represents each pixel with a single bit. A row is width pixels wide packed to the length of 8 pixels or a byte. The first pixel in a row is the most significant bit. The extra bits used to make the length equal to a byte are ignored.