rgb color model

 

  • RGB is a device-dependent color model: different devices detect or reproduce a given RGB value differently, since the color elements (such as phosphors or dyes) and their
    response to the individual red, green, and blue levels vary from manufacturer to manufacturer, or even in the same device over time.

  • Thus an RGB value does not define the same color across devices without some kind of color management.

  • [2] The main purpose of the RGB color model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has
    also been used in conventional photography and colored lighting.

  • For images with a modest range of brightnesses from the darkest to the lightest, eight bits per primary color provides good-quality images, but extreme images require more
    bits per primary color as well as the advanced display technology.

  • Additive colors To form a color with RGB, three light beams (one red, one green, and one blue) must be superimposed (for example by emission from a black screen or by reflection
    from a white screen).

  • Increased shading has been implemented in various ways, some formats such as .png and .tga files among others using a fourth greyscale color channel as a masking layer, often
    called RGB32.

  • RGB24 and RGB32 This indirect scheme restricts the number of available colors in an image CLUT—typically 256-cubed (8 bits in three color channels with values of 0–255)—although
    each color in the RGB24 CLUT table has only 8 bits representing 256 codes for each of the R, G, and B primaries, making 16,777,216 possible colors.

  • The Quattron released by Sharp uses RGB color and adds yellow as a sub-pixel, supposedly allowing an increase in the number of available colors.

  • The RGB color model is an additive color model[1] in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of
    colors.

  • [5][6] This is essentially opposite to the subtractive color model, particularly the CMY color model, which applies to paints, inks, dyes and other substances whose color
    depends on reflecting certain components (frequencies) of the light under which we see them.

  • Before the electronic age, the RGB color model already had a solid theory behind it, based in human perception of colors.

  • The RGB color model itself does not define what is meant by red, green, and blue colorimetrically, and so the results of mixing them are not specified as absolute, but relative
    to the primary colors.

  • It so happens that there is no color component among magenta, cyan and yellow, thus rendering a spectrum of zero intensity, black.

  • This data goes either to three digital-to-analog converters (for analog monitors), one per primary color or directly to digital monitors.

  • Image data that uses indexed color specifies addresses within the CLUT to provide the required R, G, and B values for each specific pixel, one pixel at a time.

  • The RGB color model is additive in the sense that if light beams of differing color (frequency) are superposed in space their light spectra adds up, wavelength for wavelength,
    to make up a resulting, total spectrum.

  • Similarly, the intensity of the output on TV and computer display devices is not directly proportional to the R, G, and B applied electric signals (or file data values which
    drive them through digital-to-analog converters).

  • Thus, the orange appearance of an object results from light from the object entering our eye and stimulating the different cones simultaneously but to different degrees.

  • This type of video signal is widely used in Europe since it is the best quality signal that can be carried on the standard SCART connector.

  • Use of the three primary colors is not sufficient to reproduce all colors; only colors within the color triangle defined by the chromaticities of the primaries can be reproduced
    by additive mixing of non-negative amounts of those colors of light.

  • Current typical display adapters use up to 24-bits of information for each pixel: 8-bit per component multiplied by three components (see the Numeric representations section
    below (each primary value of 8 bits with values of 0–255).

  • Each color has its own address (index)—consider it as a descriptive reference number that provides that specific color when the image needs it.

  • RGB information can be either carried directly by the pixel bits themselves or provided by a separate color look-up table (CLUT) if indexed color graphic modes are used.

  • Modern systems encode pixel color values by devoting eight bits to each of the R, G, and B components.

  • The first manufacturer of a truecolor graphics card for PCs was Truevision in 1987, but it was not until the arrival of the Video Graphics Array in 1987 that RGB became popular,
    mainly due to the analog signals in the connection between the adapter and the monitor which allowed a very wide range of RGB colors.

  • The difference in the signals received from the three kinds allows the brain to differentiate a wide gamut of different colors, while being most sensitive (overall) to yellowish-green
    light and to differences between hues in the green-to-orange region.

  • Video electronics[edit] Main article: Component_video § RGB_analog_component_video RGB is also the term referring to a type of component video signal used in the video electronics
    industry.

  • Physical principles for the choice of red, green, and blue The choice of primary colors is related to the physiology of the human eye; good primaries are stimuli that maximize
    the difference between the responses of the cone cells of the human retina to light of different wavelengths, and that thereby make a large color triangle.

  • By using an appropriate combination of red, green, and blue intensities, many colors can be displayed.

  • Images were scanned electrically, but the system still used a moving part: the transparent RGB color wheel rotating at above 1,200 rpm in synchronism with the vertical scan.

  • Each pixel on the screen is built by driving three small and very close but still separated RGB light sources.

  • When one of the components has the strongest intensity, the color is a hue near this primary color (red-ish, green-ish, or blue-ish), and when two components have the same
    strongest intensity, then the color is a hue of a secondary color (a shade of cyan, magenta or yellow).

  • Zero intensity for each component gives the darkest color (no light, considered the black), and full intensity of each gives a white; the quality of this white depends on
    the nature of the primary light sources, but if they are properly balanced, the result is a neutral white matching the system’s white point.

  • Nonlinearity[edit] Main article: Gamma correction In classic CRT devices, the brightness of a given point over the fluorescent screen due to the impact of accelerated electrons
    is not proportional to the voltages applied to the electron gun control grids, but to an expansive function of that voltage.

  • [3][4] Typical RGB input devices are color TV and video cameras, image scanners, and digital cameras.

  • When the exact chromaticities of the red, green, and blue primaries are defined, the color model then becomes an absolute color space, such as sRGB or Adobe RGB; see RGB color
    space for more details.

  • [19] To obtain the correct response, a gamma correction is used in encoding the image data, and possibly further corrections as part of the color calibration process of the
    device.

  • RGB signal formats are often based on modified versions of the RS-170 and RS-343 standards for monochrome video.

  • Typical RGB output devices are TV sets of various technologies, computer and mobile phone displays, video projectors, multicolor LED displays and large screens such as the
    Jumbotron.

  • For example, brightest saturated red is written in the different RGB notations as: In many environments, the component values within the ranges are not managed as linear (that
    is, the numbers are nonlinearly related to the intensities that they represent), as in digital cameras and TV broadcasting and receiving due to gamma correction, for example.

  • Color depth[edit] Main article: Color depth The RGB color model is one of the most common ways to encode color in computing, and several different digital representations
    are in use.

  • • High-end digital image equipment are often able to deal with larger integer ranges for each primary color, such as 0..1023 (10 bits), 0..65535 (16 bits) or even larger,
    by extending the 24-bits (three 8-bit values) to 32-bit, 48-bit, or 64-bit units (more or less independent from the particular computer’s word size).

  • This approach allows computations of the color similarity of two given RGB colors by simply calculating the distance between them: the shorter the distance, the higher the
    similarity.

  • Encodings of 1, 2, 4, 5, 8 and 16 bits per color are commonly found; the total number of bits used for an RGB color is typically called the color depth.

  • [33] RGB model and luminance–chrominance formats relationship All luminance–chrominance formats used in the different TV and video standards such as for component video use
    color difference signals, by which RGB color images can be encoded for broadcasting/recording and later decoded into RGB again to display them.

  • Also, other processes used to be applied in order to map the camera RGB measurements into a standard RGB color space as sRGB.

  • All images and colors are interpreted as being sRGB (unless another color space is specified) and all modern displays can display this color space (with color management being
    built in into browsers[26][27] or operating systems[28]).

  • The main characteristic of all of them is the quantization of the possible values per component (technically a sample ) by using only integer numbers within some range, usually
    from 0 to some power of two minus one to fit them into some bit groupings.

  • Also, those color difference signals need lower data bandwidth compared to full RGB signals.

  • ICC profile compliant applications, such as Adobe Photoshop, use either the Lab color space or the CIE 1931 color space as a Profile Connection Space when translating between
    color spaces.

  • Geometric representation Since colors are usually defined by three components, not only in the RGB model, but also in other color models such as CIELAB and Y’UV, among others,
    then a three-dimensional volume is described by treating the component values as ordinary Cartesian coordinates in a Euclidean space.

  • Color management results in several transparent conversions between device-independent[23] and device-dependent color spaces (RGB and others, as CMYK for color printing) during
    a typical production cycle, in order to ensure color consistency throughout the process.

  • • Each color component value can also be written as a percentage, from 0% to 100%.

  • See the actual web safe color palette for a visual confirmation that the majority of the colors produced are very dark.

  • RGB and cameras[edit] The Bayer filter arrangement of color filters on the pixel array of a digital image sensor In color television and video cameras manufactured before
    the 1990s, the incoming light was separated by prisms and filters into the three RGB primary colors feeding each color into a separate video camera tube (or pickup tube).

  • They can be considered the successors of early telephotography input devices, which were able to send consecutive scan lines as analog amplitude modulation signals through
    standard telephonic lines to appropriate receivers; such systems were in use in press since the 1920s to the mid-1990s.

  • Colors in web-page design Initially, the limited color depth of most video hardware led to a limited color palette of 216 RGB colors, defined by the Netscape Color Cube.

  • The sRGB color space (a device-independent color space[23]) for HTML was formally adopted as an Internet standard in HTML 3.2, though it had been in use for some time before
    that.

  • This representation is used in theoretical analyses, and in systems that use floating point representations.

  • Numeric representations A color in the RGB color model is described by indicating how much of each of the red, green, and blue is included.

 

Works Cited

[‘Robert Hirsch (2004). Exploring Colour Photography: A Complete Guide. Laurence King Publishing. ISBN 1-85669-420-8.
2. ^ Fairman, Hugh S.; Brill, Michael H.; Hemmendinger, Henry (February 1997). “How the CIE 1931 color-matching functions were derived
from Wright-Guild data”. Color Research & Application. 22 (1): 11–23. doi:10.1002/(SICI)1520-6378(199702)22:1
<11::AID-COL4>3.0.CO;2-7. The first of the resolutions offered to the 1931 meeting defined the color-matching functions of the soon-to-be-adopted standard observer in terms of Guild’s spectral primaries centered on wavelengths 435.8, 546.1, and 700nm. Guild approached
the problem from the viewpoint of a standardization engineer. In his mind, the adopted primaries had to be producible with national-standardizing-laboratory accuracy. The first two wavelengths were mercury excitation lines, and the last named
wavelength occurred at a location in the human vision system where the hue of spectral lights was unchanging with wavelength. Slight inaccuracy in production of the wavelength of this spectral primary in a visual colorimeter, it was reasoned,
would introduce no error at all.
3. ^ GrantMeStrength (30 December 2021). “Device-Dependent Color Spaces – Win32 apps”. learn.microsoft.com. Retrieved 2022-10-24.
4. ^ Crean, Buckley. “Device Independent Color—Who Wants It?” (PDF). SPIE. 2171:
267.
5. ^ Charles A. Poynton (2003). Digital Video and HDTV: Algorithms and Interfaces. Morgan Kaufmann. ISBN 1-55860-792-7.
6. ^ Nicholas Boughen (2003). Lightwave 3d 7.5 Lighting. Wordware Publishing, Inc. ISBN 1-55622-354-4.
7. ^ Jump
up to:a b c R. W. G. Hunt (2004). The Reproduction of Colour (6th ed.). Chichester UK: Wiley–IS&T Series in Imaging Science and Technology. ISBN 0-470-02425-9.
8. ^ Photographer to the Tsar: Sergei Mikhailovich Prokudin-Gorskii Library of Congress.
9. ^
“The Evolution of Color Pigment Printing”. Artfacts.org. Retrieved 2013-04-29.
10. ^ John Logie Baird, Television Apparatus and the Like, U.S. patent, filed in U.K. in 1928.
11. ^ Baird Television: Crystal Palace Television Studios. Previous
color television demonstrations in the U.K. and U.S. had been via closed circuit.
12. ^ “Color Television Success in Test”. NY Times. 1940-08-30. p. 21. Retrieved 2008-05-12.
13. ^ “CBS Demonstrates Full Color Television,” Wall Street Journal,
Sept. 5, 1940, p. 1.
14. ^ “Television Hearing Set”. NY Times. 1940-11-13. p. 26. Retrieved 2008-05-12.
15. ^ Morton, David L. (1999). “Television Broadcasting”. A History of Electronic Entertainment Since 1945 (PDF). IEEE. ISBN 0-7803-9936-6.
Archived from the original (PDF) on March 6, 2009.
16. ^ Domestic and similar electronic equipment interconnection requirements: Peritelevision connector (PDF). British Standards Institution. 15 June 1998. ISBN 0580298604.
17. ^ “Composite
video vs composite sync and Demystifying RGB video”. www.retrogamingcables.co.uk. Retrieved 2022-10-24.
18. ^ By directory search
19. ^ Steve Wright (2006). Digital Compositing for Film and Video. Focal Press. ISBN 0-240-80760-X.
20. ^ Edwin
Paul J. Tozer (2004). Broadcast Engineer’s Reference Book. Elsevier. ISBN 0-240-51908-6.
21. ^ John Watkinson (2008). The art of digital video. Focal Press. p. 272. ISBN 978-0-240-52005-6.
22. ^ For a side-by-side comparison of proper colors
next to their equivalent lacking proper gamma correction, see Doucette, Matthew (15 March 2006). “Color List”. Xona Games.
23. ^ Jump up to:a b “Device-Independent Color Spaces – MATLAB & Simulink”. www.mathworks.com.
24. ^ “HTML 3.2 Reference
Specification”. 14 January 1997.
25. ^ “A Standard Default Color Space for the Internet – sRGB”. W3C.
26. ^ “Color management in Internet”. www.color-management-guide.com.
27. ^ “How to setup proper color management in your web browser –
Greg Benz Photography”. gregbenzphotography.com. April 27, 2021.
28. ^ “About Color Management”. support.microsoft.com.
29. ^ “Wide Gamut Color in CSS with Display-P3”. March 2, 2020.
30. ^ “”color” Can I use… Support tables for HTML5,
CSS3, etc”. Can I use…
31. ^ “Wide Gamut Color in CSS with Display-P3”. March 2, 2020.
32. ^ “CSS color() function”. Can I use…
33. ^ ICC. “Why Color Management?” (PDF). Retrieved 2008-04-16. The two PCS’s in the ICC system are CIE-XYZ
and CIELAB
Photo credit: https://www.flickr.com/photos/seven_of9/5994572653/’]