question: If computer/tv screens operate on projecting an image through light, how do they convey shades of black?
comment: Full disclosure, with some newer technologies maybe this has changed, but it used to be that screens were designed to present as black as possible without any kind of light source behind them. When the color black was required, the television/monitor would simply not display any colors to that particular “dot”. So it was truly just an absence of light you saw.
passages: A "shade" is produced by "dimming" a hue. Painters refer to this as "adding black". In our illustration, one projector is set to full intensity, a second is set to some intensity between zero and full, and third is set to zero. "Dimming" is accomplished by decreasing each projector's intensity setting to the same fraction of its start setting.
  
  In the shade example, with any fully shaded hue, that all three projectors are set to zero intensity, resulting in black.
   All emissive electronic displays (e.g. CRTs, PDPs) theoretically do not emit light in the black state (R=G=B=0%) and thus, under darkroom conditions with no ambient light reflected from the display surface into the light measuring device, the luminance of the black state is zero and thus the contrast becomes infinity.
  
  When these display-screens are used outside a completely dark room, e.g. in the living room (illuminance approx. 100 lx) or in an office situation (illuminance 300 lx minimum), ambient light is reflected from the display surface, adding to the luminance of the dark state and thus reducing the contrast considerably.
   However, darkest black in a projected image is dependent on how dark the screen is. Because of this, some presenters and presentation-space planners prefer gray screens, which create higher-perceived contrast. The trade-off is that darker backgrounds can throw off color tones. Color problems can sometimes be adjusted through the projector settings, but may not be as accurate as they would on a white background.
  
  Section::::Throw ratio.
   Some increase in dynamic range in LCD monitors can be achieved by automatically reducing the backlight for dark scenes. For example, LG calls this technology "Digital Fine Contrast"; Samsung describes it as "dynamic contrast ratio". Another technique is to have an array of brighter and darker LED backlights, for example with systems developed by BrightSide Technologies.
  
  OLED displays have better dynamic range capabilities than LCDs, similar to plasma but with lower power consumption. Rec. 709 defines the color space for HDTV, and Rec. 2020 defines a larger but still incomplete color space for ultra-high-definition television.
  
  Section::::Limitations and compensations.:Light bloom.
   Because LEDs can be switched on and off more quickly than CCFLs and can offer a higher light output, it is theoretically possible to offer very high contrast ratios. They can produce deep blacks (LEDs off) and high brightness (LEDs on). However, measurements made from pure-black and pure-white outputs are complicated by the fact that edge-LED lighting does not allow these outputs to be reproduced simultaneously on screen.
  
  Full-array backlights that use mini-LED panels, consisting of several thousand WLEDs, are being researched for TVs and mobile devices.
  
  Section::::Technology.:Quantum dot enhancement film.
   An OLED display works without a backlight. Thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions such as a dark room, an OLED screen can achieve a higher contrast ratio than an LCD, whether the LCD uses cold cathode fluorescent lamps or LED backlight.
  
  Section::::Outdoor television.
   The concept behind Blackle is that computer monitors can be made to use less energy by displaying much darker colors. Blackle is based on a study which tested a variety of CRT and LCD monitors. There is dispute over whether there really are any energy saving effects, especially for users of LCD screens, where there is a constant backlight.
   Red, green, and blue light combined at full intensity on the black screen makes white; by lowering the intensity, it is possible to create different shades of grey.
   Tru Black is a technology developed by Sony which allows a better visualization of the screen, even when there is too much light. It enables LCD screens to automatically change the display contrast in order to enhance the controlling reflectance. In other words, when light hits a display with Tru Black technology, the screen turns opaque as a means to improve the visualization of the content. 
  
  Section::::Features.:Panorama.
   Section::::History of DIY painted screens.
  
  Projection screens are primarily white or gray. A white screen is better balanced and more accurate when it is close to D65 (the international standard illumination conditions). A gray screen is more accurate when it is closer to neutral, based on parameters such as color balance (L*ab and xyY values), spectral curve and color temperature.
   Additive color models are applied in the design and testing of electronic displays that are used to render realistic images containing diverse sets of color using phosphors that emit light of a limited set of primary colors. Examination with a sufficiently powerful magnifying lens will reveal that each pixel in CRT, LCD, and most other types of color video displays is composed of red, green, and blue light emitting phosphors which appear as a variety of single colors when viewed from a normal distance.
   Care must be taken when using electronic design programs (e.g. when managing a CMYK document in Adobe Illustrator or Corel Draw) – "black" may or may not equal 100%K depending on the CMYK profile specified in the image's settings, and Photoshop will represent the various tones using RGB values close to black; in an RGB document, "black" always equals RGB value (0, 0, 0).
   There are 2 types of monitors, they are "Monochrome & Colored Monitors". "Monochrome" monitors actually display two colors, one for the foreground and one for the background. The colors can be black and white, green and black, or amber and black. The "Colored Monitor" is a display device capable of displaying many colors. The Color monitors can display anywhere from 16 to over 1 million different colors.
  
  Section::::Display devices about-.:Types of Display (Monitor).:Monochrome Display.
   CCFL backlighting has also improved in this respect. Many LCD models, from cheap TN-displays to color proofing S-IPS or S-PVA panels, have wide gamut CCFLs representing more than 95% of the NTSC color specification.
   The screens are typically covered with phosphor using sedimentation coating, where particles suspended in a solution are let to settle on the surface.
  
  Section::::Applications.:Cathode ray tubes.:Reduced-palette color CRTs.
  
  For displaying of a limited palette of colors, there are a few options.
   The ghosting effects of the now-obsolete green screens have become an eye-catching visual shorthand for computer-generated text, frequently in "futuristic" settings. The opening titles of the first "Ghost in the Shell" film and the Matrix source code of the Matrix trilogy science fiction films prominently feature computer displays with ghosting green text. Green text is also featured in 's computer in "Lost" series.
  
  Section::::Phosphor limitations.
  
  Monochrome monitors are particularly susceptible to screen burn (hence the advent, and name, of the screensaver), because the phosphors used are of very high intensity.
   The black level of a single-chip DLP depends on how unused light is being disposed. If the unused light is scattered to reflect and dissipate on the rough interior walls of the DMD / lens chamber, this scattered light will be visible as a dim gray on the projection screen, when the image is fully dark. Deeper blacks and higher contrast ratios are possible by directing unused HID light away from the DMD / lens chamber into a separate area for dissipation, and shielding the light path from unwanted internal secondary reflections.
   An OLED display works without a backlight because it emits visible light. Thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions (such as a dark room), an OLED screen can achieve a higher contrast ratio than an LCD, regardless of whether the LCD uses cold cathode fluorescent lamps or an LED backlight.
  
  Section::::History.
   A metric for "color contrast" often used in the electronic displays field is the color difference ΔE*uv or ΔE*ab.
  
  Section::::Full-screen contrast.
  
  During measurement of the luminance values used for evaluation of the contrast, the active area of the display screen is often completely set to one of the optical states for which the contrast is to be determined, e.g. completely white (R=G=B=100%) and completely black (R=G=B=0%) and the luminance is measured one after the other (time sequential).
   Color displays (e.g. computer monitors and televisions) cannot reproduce "all" colors discernible by a human eye. Colors outside the color gamut of the device, such as most spectral colors, can only be approximated. For color-accurate reproduction, a spectrum can be projected onto a uniform gray field. The resulting mixed colors can have all their R, G, B coordinates non-negative, and so can be reproduced without distortion. This accurately simulates looking at a spectrum on a gray background.
  
  Section::::Spectroscopy.
   In order to measure the highest contrast possible, the dark state of the display under test must not be corrupted by light from the surroundings, since even small increments ΔL in the denominator of the ratio (L + ΔL) / (L + ΔL) effect a considerable reduction of that quotient. This is the reason why most contrast ratios used for advertising purposes are measured under dark-room conditions (illuminance E ≤ 1 lx).
   Normally, the software in a computer treats the computer’s display screen as a rectangular array of square, indivisible pixels, each of which has an intensity and color that are determined by the blending of three primary colors: red, green, and blue. However, actual display hardware usually implements each pixel as a group of three adjacent, independent "subpixels," each of which displays a different primary color. Thus, on a real computer display, each pixel is actually composed of separate red, green, and blue subpixels. For example, if a flat-panel display is examined under a magnifying glass, the pixels may appear as follows:
   Unlike color monitors, which display text and graphics in multiple colors through the use of alternating-intensity red, green, and blue phosphors, monochrome monitors have only one color of phosphor ("mono" means "one", and "chrome" means "color"). All text and graphics are displayed in that color. Some monitors have the ability to vary the brightness of individual pixels, thereby creating the illusion of depth and color, exactly like a black-and-white television.
   An OLED display works without a backlight. Thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions such as a dark room an OLED screen can achieve a higher contrast ratio than an LCD, whether the LCD uses cold cathode fluorescent lamps or LED backlight. OLEDs are expected to replace other forms of display in near future.
  
  Section::::Sets.:Display resolution.
  
  Section::::Sets.:Display resolution.:LD.
   The remainder of the LCD uses existing display technology and can be made using existing manufacturing equipment. Even the masks can be made using combinations of existing materials and processes.
  
  When lit primarily from the rear with the white LED backlight, the display shows a color image composed of both RGB and grayscale information. When lit primarily from the front by ambient light, for example from the sun, the display shows a monochromatic (black and white) image composed of just the grayscale information.
  
presuppositions: Computer and TV screens convey shades of black when they shouldn't be able to.  Computer screens and TV screens display shades of black when it should not be possible to do so.  Computer and television screens convey shades of the color black.
corrections: Computer and TV screens don't actually display black, they simply stop displaying all other colors which provides the equivalent of a black screen.  Computer screens and TV screens do not display shades of black, they simply remove all other colors which shows the color black without actually needing the shade of black.  Computer and television screens don't actually convey shades of the color black, when the color black is required to be shown, the screen will display no colors at all which will provide the equivalent to a shade of black.
raw_presuppositions: Computer and TV screens convey shades of black when they shouldn't be able to.  Computer screens and TV screens display shades of black when it should not be possible to do so.  Computer and television screens convey shades of the color black. screens convey shades of black
raw_corrections: Computer and TV screens don't actually display black, they simply stop displaying all other colors which provides the equivalent of a black screen.  Computer screens and TV screens do not display shades of black, they simply remove all other colors which shows the color black without actually needing the shade of black.  Computer and television screens don't actually convey shades of the color black, when the color black is required to be shown, the screen will display no colors at all which will provide the equivalent to a shade of black. monitor would simply not display anything to that dot