Binary image

A photograph of a Neighborhood Watch sign in black and white (binary)

A binary image is a digital image that has only two possible values for each pixel. ^[1] Typically the two colors used for a binary image are black and white though any two colors can be used. ^[1] The color used for the object(s) in the image is the foreground color while the rest of the image is the background color. ^[1]

Binary images are also called bi-level or two-level. This means that each pixel is stored as a single bit (0 or 1). The names black-and-white, B&W, monochrome or monochromatic are often used for this concept, but may also designate any images that have only one sample per pixel, such as grayscale images. In Photoshop parlance, a binary image is the same as an image in "Bitmap" mode.

Binary images often arise in digital image processing as masks or as the result of certain operations such as segmentation, thresholding, and dithering. Some input/output devices, such as laser printers, fax machines, and bilevel computer displays, can only handle bilevel images.

A binary image is usually stored in memory as a bitmap, a packed array of bits. A 640×480 image requires 37.5 KiB of storage.

Binary images can be interpreted as subsets of the two-dimensional integer lattice Z²; the field of morphological image processing was largely inspired by this view.

Interpretation

The interpretation of the pixel's binary value is also device-dependent. Some systems interprets the bit value of 0 as black and 1 as white, while others reversed the meaning of the values. These are known as vanilla and chocolate flavors in the TWAIN standard PC interface for scanners and digital cameras.

Dithering is often used for displaying halftone images.

See also

• Black-and-white
• Connected Component Labeling
• Netpbm format
• JBIG/JBIG2
• X BitMap

References