Cromaclear is a trademark for CRT technology used by NEC during the mid to late-90s. This adopted the slotted shadow mask and in-line electron gun pioneered by the 1966 GE Porta-Color and used by most then-current television tubes to computer monitor use. It was claimed that Cromaclear could offer the image clarity and sharpness of the Trinitron and Diamondtronaperture grille CRTs without the disadvantages e.g. expense and the horizontal damping wires.
The most significant difference between Cromaclear CRTs and existing CRT computer monitor technologies is their phosphor pattern. Older color televisions and most CRT monitors have a pattern of round dots arranged in a triangular mosaic. Slot-mask CRTs have a pattern of stripes in the unlit phosphor that appears to be bricks when in use. The slots block less of the electron beam than dots, resulting in a brighter picture.
With Cromaclear CRTs, the conventional "dot pitch" measurement is no longer as accurate. The term "mask pitch" is more appropriate when discussing this specification. A mask pitch measurement is the distance between like-colored phosphors on a Cromaclear mask. The mask pitch of a Cromaclear screen is 0.25mm.[clarification needed]
Image quality
Overall monitor image quality is difficult to quantify. Given the inherent complex nature of CRTs, a variety of factors combine to produce a monitor’s image. These factors — focus, contrast and color saturation — all come into play when deciding which monitor and technology provides the "best" image. When discussed in relation to Cromaclear, these items need further explanation.
Focus: Cromaclear incorporates a new SDF-ELA (Single Dynamic Focus - Expanded Large Aperture) gun for 15-inch tubes and DQF- ELA (Dynamic Quadrupole Focus - Expanded Large Aperture) gun for 17-inch tubes. These guns provide uniform image clarity and focus. When viewing images in monitor's corners, other CRTs could distort image ratio and perspective. Using the Cromaclear-specific ELA gun, this problem is virtually eliminated. This also provides improvements for viewing six-point text and fine, single-pixel elements.
As a consequence of Cromaclear's new mask form, the electron beam used to pass through the slot mask had to be adapted to match. The ELA gun utilized for Cromaclear has an exact beam/mask match (an elliptical electron beam passes through an elliptical mask opening) for optimum power transfer from electron beam to screen phosphors.
Although it was possible to use existing round phosphor gun technology with Cromaclear, a certain percentage of electron power would have been lost, thereby degrading overall image focus. An effective visual to describe this phenomenon is a "round peg, square hole" analogy: while contact might be taking place, it’s not completely precise. Excess energy transfer could lead to a warped grille or mask, resulting in possible image degradation (color purity and/or brightness uniformity problems). This mismatch tends to occur in aperture grille CRTs (stripe grille/circular electron beam). On the other hand, shadow mask CRTs match a circular beam to a circular shadow mask.
This combination of dynamic beam focus and new electron guns also reduces the need for end-user moiré and convergence controls while enhanced brightness provides improved contrast.
Convergence
Convergence is the process of controlling the CRT beam deflection to keep the red, green and blue beams properly overlapped when scanning the raster (area illuminated by the scan lines on a CRT). As the electron gun scans across the screen, the shape of electron beams slightly varies as the beam reaches the outer edges of the screen. Misconvergence, the technical term used when this process is not completely accurate, appears as color fringing on the edge of an image displayed on the screen. For example, a CRT monitor with misaligned electron beams will show a white "H" on a black background with one of the primary or secondary colors shadowing its edges. Cromaclear provides deterrents to misconvergence, including the ELA guns and their tight mask pitch.
Cromaclear vs. aperture grille CRTs
Comparison between in-line shadow mask (left) and aperture grille (right) based CRTs
Aperture grille CRT monitors currently use damping wires to hold the black striping in place between the phosphors. Comparatively, Cromaclear utilizes a type of shadow mask that does not require the use of damping wires. Damping wires can sometimes be visible to the user under extreme white plain background displays and mechanically obstruct the flow of the electron beams, critical to maximizing image focus. The Cromaclear shadow mask, however, still has much more impeding metal than an aperture grill mask, leading overall to a darker, softer picture than the equivalent aperture grill CRT. The impact of damping wires of the aperture grill CRT, is far less than the total extra metal in the cromaclear mask which is effectively like having a thick damping wire for each row of phosphor. This in turn means that the cromaclear CRT needs a much more powerful electron beam to illuminate the phosphors brightly, which reduces the overall life of the CRT and its focusing ability, which is the most expensive part of any CRT monitor or television.
Damping wires are sensitive and are more susceptible to shipping damage, but usually the glass would be broken before the damping wires give way, making aperture grill CRTs equally robust to any other under normal conditions. They also have the potential to be affected by harmonic distortion when speakers are placed near the CRT, however for this to be a visible problem the speakers would need to be impractically close to the screen and producing a very high sound output, so in effect this effect would have to be contrived by speaker position rather than a problem in operation.
Additionally since aperture grill CRTs have no "horizontal" elements to the shadow mask, the resolution of the CRT in the vertical direction is limited by the focus of the electron beam and the granularity of the phosphor, unlike Cromaclear and other shadow mask based CRTs whose vertical resolution is limited by the number of rows of metal in the mask.
Cromaclear vs. "conventional" shadow mask CRTs
Comparison between in-line shadow mask (left) and delta shadow mask (right) based CRTs
Cromaclear CRTs improve upon the image sharpness and focus attributed to shadow mask based dot trio CRTs. The slot mask design and illuminated phosphor alignment provide a tighter mask pitch, leading to improved image quality. In addition, the tighter mask pitch and ELA guns enhance focus and combat moiré.
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictures, radar targets, or other phenomena. A CRT on a television set is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.
An aperture grille is one of two major technologies used to manufacture color cathode-ray tube (CRT) televisions and computer displays; the other is the shadow mask.
The shadow mask is one of the two technologies used in the manufacture of cathode-ray tube (CRT) televisions and computer monitors which produce clear, focused color images. The other approach is the aperture grille, better known by its trade name, Trinitron. All early color televisions and the majority of CRT computer monitors used shadow mask technology. Both of these technologies are largely obsolete, having been increasingly replaced since the 1990s by the liquid-crystal display (LCD).
Trinitron was Sony's brand name for its line of aperture-grille-based CRTs used in television sets and computer monitors. One of the first truly innovative television systems to enter the market since the 1950s, the Trinitron was announced in 1968 to wide acclaim for its bright images, about 25% brighter than common shadow mask televisions of the same era. Constant improvement in the basic technology and attention to overall quality allowed Sony to charge a premium for Trinitron devices into the 1990s.
Dot pitch is a specification for a computer display, computer printer, image scanner, or other pixel-based devices that describe the distance, for example, between dots (sub-pixels) on a display screen. In the case of an RGB color display, the derived unit of pixel pitch is a measure of the size of a triad plus the distance between triads.
In cathode-ray tube (CRT), or computer display terminology, a triad is a group of 3 phosphor dots coloured red, green, and blue on the inside of the CRT display of a computer monitor or television set. By directing differing intensities of electron beams onto the 3 phosphor dots, the triad will display a colour by combining the red, green and blue elements. However, triads are not pixels, and multiple triads will form one logical pixel of the displayed image.
An electron gun is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy.
Direct-view bistable storage tube (DVBST) was an acronym used by Tektronix to describe their line of storage tubes. These were cathode ray tubes (CRT) that stored information written to them using an analog technique inherent in the CRT and based upon the secondary emission of electrons from the phosphor screen itself. The resulting image was visible in the continuously glowing patterns on the face of the CRT.
A surface-conduction electron-emitter display (SED) is a display technology for flat panel displays developed by a number of companies. SEDs use nanoscopic-scale electron emitters to energize colored phosphors and produce an image. In a general sense, a SED consists of a matrix of tiny cathode-ray tubes, each "tube" forming a single sub-pixel on the screen, grouped in threes to form red-green-blue (RGB) pixels. SEDs combine the advantages of CRTs, namely their high contrast ratios, wide viewing angles, and very fast response times, with the packaging advantages of LCD and other flat panel displays. They also use much less power than an LCD television of the same size.
This is a comparison of various properties of different display technologies.
The penetron, short for penetration tube, is a type of limited-color television used in some military applications. Unlike a conventional color television, the penetron produces a limited color gamut, typically two colors and their combination. Penetrons, and other military-only cathode ray tubes (CRTs), have been replaced by LCDs in modern designs.
Large-screen television technology developed rapidly in the late 1990s and 2000s. Prior to the development of thin-screen technologies, rear-projection television was standard for larger displays, and jumbotron, a non-projection video display technology, was used at stadiums and concerts. Various thin-screen technologies are being developed, but only liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been publicly released. Recent technologies like organic light-emitting diode (OLED) as well as not-yet-released technologies like surface-conduction electron-emitter display (SED) or field emission display (FED) are in development to replace earlier flat-screen technologies in picture quality.
A vector monitor, vector display, or calligraphic display is a display device used for computer graphics up through the 1970s. It is a type of CRT, similar to that of an early oscilloscope. In a vector display, the image is composed of drawn lines rather than a grid of glowing pixels as in raster graphics. The electron beam follows an arbitrary path tracing the connected sloped lines, rather than following the same horizontal raster path for all images. The beam skips over dark areas of the image without visiting their points.
A monochrome monitor is a type of computer monitor in which computer text and images are displayed in varying tones of only one color, as opposed to a color monitor that can display text and images in multiple colors. They were very common in the early days of computing, from the 1960s through the 1980s, before color monitors became widely commercially available. They are still widely used in applications such as computerized cash register systems, owing to the age of many registers. Green screen was the common name for a monochrome monitor using a green "P1" phosphor screen; the term is often misused to refer to any block mode display terminal, regardless of color, e.g., IBM 3279, 3290.
The Chromatron is a color television cathode ray tube design invented by Nobel prize-winner Ernest Lawrence and developed commercially by Paramount Pictures, Sony, Litton Industries and others. The Chromatron offered brighter images than conventional color television systems using a shadow mask, but a host of development problems kept it from being widely used in spite of years of development. Sony eventually abandoned it in favor of their famous Trinitron system using an aperture grille.
The Geer tube was an early single-tube color television cathode ray tube, developed by Willard Geer. The Geer tube used a pattern of small phosphor-covered three-sided pyramids on the inside of the CRT faceplate to mix separate red, green and blue signals from three electron guns. The Geer tube had a number of disadvantages, and was never used commercially due to the much better images generated by RCA's shadow mask system. Nevertheless, Geer's patent was awarded first, and RCA purchased an option on it in case their own developments didn't pan out.
The beam-index tube is a color television cathode ray tube (CRT) design, using phosphor stripes and active-feedback timing, rather than phosphor dots and a beam-shadowing mask as developed by RCA. Beam indexing offered much brighter pictures than shadow-mask CRTs, reducing power consumption, and as they used a single electron gun rather than three, they were easier to build and required no alignment adjustments.
General Electric's Porta-Color was the first "portable" color television introduced in the United States in 1966.
This is a subdivision of the Oscilloscope article, discussing the various types and models of oscilloscopes in greater detail.
The Triniscope was an early color television system developed by RCA. It used three separate video tubes with colored phosphors producing the primary colors, combining the images through dichroic mirrors onto a screen for viewing.
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