A typical grayscale image.

In computing, a grayscale or greyscale digital image is an image in which the value of each pixel is a single sample, that is, it carries the full (and only) information about its intensity. Images of this sort are composed exclusively of shades of neutral gray, varying from black at the weakest intensity to white at the strongest. For the formal concept of computation, see computation. ... A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. ... This article is about the picture element. ... A sample refers to a value or set of values at a point in time and/or space. ... In physics, intensity is a measure of the time-averaged energy flux. ... Gray (Gy) is the derived SI unit for absorbed dose, specific energy and kerma (kinetic energy in matter). ...

Grayscale images are distinct from black-and-white images, which in the context of computer imaging are images with only two colors, black and white (also called bilevel, binary images or more commonly bitmapped images); grayscale images have many shades of gray in between. In most contexts other than digital imaging, however, the term "black and white" is used in place of "grayscale"; for example, photography in shades of gray is typically called "black-and-white photography". The term monochromatic in some digital imaging contexts is synonymous with grayscale (as it denotes absence of any concrete hue), and in some contexts synonymous with black-and-white. Black-and-white or black and white) can refer to a general term used in photography, film, and other media (see black-and-white). ... Color is an important part of the visual arts. ... This article is about the color. ... This article is about the color. ... A binary image is a digital image that has only two possible values for each pixel. ... Something which is monochromatic has a single color. ... An image with the hues cyclically shifted The hues in the image of this Painted Bunting are cyclically rotated with time. ...

Grayscale images are often the result of measuring the intensity of light at each pixel in a single band of the electromagnetic spectrum (e.g. infrared, visible light, ultraviolet, etc.), and in such cases they are monochromatic proper when only a given frequency is captured. But also they can be synthesized from a full color image; see the section about converting to grayscale. Legend γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... For other uses, see Infrared (disambiguation). ... Visible light redirects here. ... For other uses, see Ultraviolet (disambiguation). ... For other uses, see Frequency (disambiguation). ...

Numerical representations

4096 gray levels

The intensity of a pixel is expressed within a given range between a minimum and a maximum, inclusive. This range is represented in an abstract way as a range from 0 (total absence, black) and 1 (total presence, white), with any fractional values in between. This notation is used in academic papers, but it must be noted that this does not define what "black" or "white" is in terms of colorimetry. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... This article or section is not written in the formal tone expected of an encyclopedia article. ...

Another convention is to employ percentages, so the scale is then from 0% to 100%. This is used for a more intuitive approach, but if only integer values are used, the range encompasses a total of only 101 intensities, which are insufficient to represent a broad gradient of grays. Also, the percentile notation is used in printing to denote how much ink is employed in halftoning, but then the scale is reversed, with 0% pure white (no ink) and 100% a solid black (full ink). The percent sign. ... The integers are commonly denoted by the above symbol. ... For other uses, see Print. ... Left: Halftone dots. ...

In computing, although the grayscale can be computed through rational numbers, image pixels are stored in binary, quantized form. Some early grayscale monitors had a mere 4 bits of resolution, allowing for only 16 shades of gray, but today, grayscale images (as photographs) intended for visual display (both on screen and printed) are commonly stored with 8 bits per sampled pixel, which allows 256 different intensities (i.e., shades of gray) to be recorded, typically on a non-linear scale. The accuracy provided by this format is barely sufficient to avoid visible banding artifacts, but very convenient for programming as a single pixel occupies a single byte. In mathematics, a rational number (or informally fraction) is a ratio of two integers, usually written as the vulgar fraction a/b, where b is not zero. ... Look up binary in Wiktionary, the free dictionary. ... Quantized signal Digital signal In digital signal processing, quantization is the process of approximating a continuous range of values (or a very large set of possible discrete values) by a relatively-small set of discrete symbols or integer values. ... This article is about the unit of information. ... Example of CRT gamma correction Plot of the sRGB standard gamma-expansion nonlinearity (red), and its local gamma value, slope in log–log space (blue). ... A compression artifact (or artefact) is the result of an aggressive data compression scheme applied to an image, audio, or video that discards some data which is determined by an algorithm to be of lesser importance to the overall content but which is nonetheless discernible and objectionable to the user. ... For the computer industry magazine, see Byte (magazine). ...

Technical uses (e.g. in medical imaging or remote sensing applications) often require more levels, to make full use of the sensor accuracy (typically 10 or 12 bits per sample) and to guard against roundoff errors in computations. Sixteen bits per sample (65,536 levels) is a convenient choice for such uses, as computers manage 16-bit words efficiently. The TIFF and the PNG (among other) image file formats supports 16-bit grayscale natively, although browsers and many imaging programs tend to ignore the low order 8 bits of each pixel. Medical imaging designates the ensemble of techniques and processes used to create images of the human body (or parts thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and function). ... For the purported psychic ability to sense remotely, see Remote viewing right Synthetic aperture radar image of Death Valley colored using polarimetry In the broadest sense, remote sensing is the short or large-scale acquisition of information of an object or phenomenon, by the use of either recording or real... Not to be confused with censure, censer, or censor. ... In computing, word is a term for the natural unit of data used by a particular computer design. ... “TIFF” redirects here. ... PNG (Portable Network Graphics), sometimes pronounced as ping, is a relatively new bitmap image format that is becoming popular on the World Wide Web and elsewhere. ... Image file formats provide a standardized method of organizing and storing image data. ...

No matter what pixel depth is used, the binary representations assume that 0 is black and the maximum value (255 at 8 bpp, 65,535 at 16 bpp, etc.) is white, if not otherwise noted. Color depth is a computer graphics term describing the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. ...

Converting color to grayscale

The same picture in three different color modes. The picture on the left is the original photograph, in full color. The picture in the center is in grayscale; all the colors contained in it are black, white, or any shade of gray. The picture on the right is in black and white, or bitmap; the only colors used in the picture are black and white, with no intermediary grays.

To convert any color to its most approximate level of gray, first one must obtain the values of its red, green and blue (RGB) primaries. A Neighborhood Watch notice sign in color File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... A Neighborhood Watch notice sign in grayscale File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Size of this preview: 200 × 140 pixelsFull resolution (200 × 140 pixel, file size: 3 KB, MIME type: image/png) A Neighborhood Watch notice sign in monochrome black and white Permission is granted to copy, distribute and/or modify this document under the terms of the... REDIRECT RGB color model ...

Then, add 30% of the red value, 59% of the green value, and 11% of the blue value, together. Regardless of the scale employed (0.0 to 1.0, 0 to 255, 0% to 100%, etc.), the resultant number is the desired gray value. These percentages are chosen due to the different relative sensitivity of the normal human eye to each of the primary colors (less sensitive to green, more to blue). This article refers to the sight organ. ...

This is the method used to obtain the luminance in the YUV and related color models, used in standard color TV and video systems as PAL and NTSC, as well as in the L*a*b color model. Visit these articles for a rationale of the above formula. Relative luminance follows the photometric definition of luminance, but with the values normalized to 1 or 100 for a reference white[1]. Like the photometric definition, it is related to the luminous flux density in a particular direction, which is radiant flux density weighted by the luminosity function of the... This article or section is in need of attention from an expert on the subject. ... For other uses, see PAL (disambiguation). ... NTSC is the analog television system in use in Canada, Japan, Mexico, the Philippines, South Korea, Taiwan, the United States, and some other countries, mostly in the Americas (see map). ... Without further qualification, Lab color space refers to that of Hunter (Richard S Hunter, JOSA, 38, p 661 (1948)), which is an Adams Chromatic Valance Space. ...

To convert a gray intensity value to RGB, simply set all the three primary color components red, green and blue to the gray value, scaling if necessary (that is, when the gray and RGB component ranges are not the same).

Grayscale as single channels of multichannel color images

Color images are often built of several stacked color channels, each of them representing value levels of the given channel. For example, RGB images are composed of three independent channels for red, green and blue primary color components; CMYK images have four channels for cyan, magenta, yellow and black ink plates, etc. Being every single channel also a single sample, they can be managed easily as independent grayscale images. This article is actively undergoing a major edit. ... REDIRECT RGB color model ... This article is about colors. ... Cyan, magenta, yellow, and key (black) CMYK (or sometimes YMCK) is a subtractive color model used in color printing. ... Color printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome printing). ...

Here is an example of color channel splitting of a full RGB color image. The column at left shows the isolated color channels in natural colors, while at right there are their grayscale equivalences:

The reverse is also possible: to build a full color image from their separate grayscale channels. By mangling channels, offseting, rotating and other manipulations, artistic effects can be achieved instead to make the mere accurate original image.

Colorized grayscale

By clever use of color palettes, grayscale images can be easily colorized to both achieve artistic effects (as the sepia tone) and to map the pixels' intensities through a false color palette to study false color images in scientific fields. A palette, in computer graphics, is a designated subset of the total range of colors supported by a computer graphics system. ... Sepia tone is a type of digital photo in which the picture appears similar to a traditional black-and-white print toned with sepia. ... A false color image showing the Chesapeake Bay and the city of Baltimore. ...

At right is the previous parrot image seen using an arbitrary false color palette, which reveals additional details of the dark background areas.

See also

• Binary image
• Halftone
• False-color
• Morphological image processing
• Channel (digital image)
• Sepia tone
• Duotone
• Cyanotype
• List of monochrome and RGB palettes - Monochrome palettes section
• List of software palettes - Color gradient palettes and false color palettes sections

A binary image is a digital image that has only two possible values for each pixel. ... Left: halftone spots. ... A false color image showing the Chesapeake Bay and the city of Baltimore. ... A collection of techniques for digital image processing based on mathematical morphology. ... This article is actively undergoing a major edit. ... Sepia tone is a type of digital photo in which the picture appears similar to a traditional black-and-white print toned with sepia. ... Duotone is a form of printing halftones with two colors of ink, one usually black. ... Cyanotype is an old monochrome photographic printing process that gives a cyan-blue print. ...

External links

• Converting a Digital Color Photo Into Black and White, includes a background on color filter use in traditional film photography, how black and white conversion works, and a comparison of digital conversion techniques
• My Design Primer article
• http://www.stusharp.co.uk/GrayScaleOnline.aspx An online grayscale converter.