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104-469: The original IBM CGA graphics card was built around the Motorola 6845 display controller, came with 16  kilobytes of video memory built in, and featured several graphics and text modes . The highest display resolution of any mode was 640 × 200, and the highest color depth supported was 4-bit (16 colors). The CGA card could be connected either to a direct-drive CRT monitor using

208-505: A 4-bit digital ( TTL ) RGBI interface, such as the IBM 5153 color display, or to an NTSC -compatible television or composite video monitor via an RCA connector . The RCA connector provided only baseband video, so to connect the CGA card to a television set without a composite video input required a separate RF modulator . IBM produced the 5153 Personal Computer Color Display for use with

312-438: A CRT is left to other circuits. Because of this, systems using the 6845 may have very different numbers and values of colors, or may not support color at all. Interlaced and non-interlaced output modes are supported, as is a hardware text cursor. The sync generation includes generation of horizontal and vertical video blanking signals, which are used to condition the external pixel generation circuits. Also, an internal latch

416-418: A character code byte and the second byte is a character attribute byte—and the board uses the contents of the bytes, together with the row address, to read font data from ROM and generate the pixels. Different routing of the bits, omitting the character ROM, could be used to emulate a frame buffer. Due to its 128 line limitation, the 6845 is not able to provide linear large linear frame buffers. A solution

520-405: A character line cache. Using the full address range RA0-RA4:CA0-CA13 the 6845 can address 2 = 524,288 words of memory. A word may be any number of bits chosen by the system designer as the memory width: though the number of unique addresses that the 6845 can address is limited to 524,288 , the amount of memory that the 6845 can address may be significantly larger than might be assumed because

624-498: A few more years because the original VGA cards were palette-driven just like EGA, although with more freedom than VGA, but because the VGA connectors were analog, later variants of VGA (made by various manufacturers under the informal name Super VGA) eventually added true-color. In 1992, magazines heavily advertised true-color Super VGA hardware. One common application of the RGB color model is

728-515: A four-color palette. In mode 4, there are two palettes, and in mode 5 there is a single palette. Several choices can be made by programming hardware registers. First, the selected palette. Second, the intensity – which is defined for the entire screen, not on a per-pixel basis. Third, color 0 (the "background" color) can be set to any of the 16 colors. The specific BIOS graphics mode influences which palettes are available. BIOS Mode 4 offers two palettes: green/red/brown and cyan/magenta/white. As with

832-404: A fourth greyscale color channel as a masking layer, often called RGB32 . 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. For more information see High Dynamic Range (HDR) imaging. In classic CRT devices,

936-677: 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 . Typical RGB input devices are color TV and video cameras , image scanners , and digital cameras . Typical RGB output devices are TV sets of various technologies ( CRT , LCD , plasma , OLED , quantum dots , etc.), computer and mobile phone displays, video projectors , multicolor LED displays and large screens such as

1040-548: A greenish tint, and color 6 again looks dark yellow instead of brown. The relative luminances of the colors produced by the composite color-generating circuit differ between CGA revisions: they are identical for colors 1-6 and 9-14 with early CGAs produced until 1983, and are different for later CGAs due to the addition of additional resistors. CGA offers four BIOS text modes ( Modes 0 to 3 , called alphanumeric or A/N modes in IBM's documentation). In these modes, individual pixels on

1144-407: A higher scan rate. The effective screen resolution of this mode is 640 × 200 pixels. In this mode, the card has enough video RAM for four different text pages. As with the 40-column text modes, Mode 2 disables the color burst in the composite signal and Mode 3 enables it. Each character cell stored four bits for foreground and background color. However, in the card's default configuration,

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1248-454: A light pen interface, though it was usually an internal connector on the board itself, not on the outside of the computer, and it was usually undocumented in the user manual. Because all aspects of video timing are programmable, a single machine can switch between 50Hz and 60Hz timings in software (or indeed any other refresh rates within the limits of the chip). The 6845 can be used to drive monitors or any other raster display. The chip has

1352-511: A normal means through the BASIC language to switch the CGA from blink mode to 16-background-color mode. This was still possible however by directly programming the hardware registers using the OUT statement of the BASIC language. CGA offers graphics modes at three resolutions: 160 × 100, 320 × 200 and 640 × 200. In all modes every pixel on the screen can be set directly, but

1456-693: A pattern of 8×8 dots. The effective screen resolution in this mode is 320 × 200 pixels (a pixel aspect ratio of 1:1.2.) The card has sufficient video RAM for eight different text pages in this mode. The difference between these two modes can only be seen on a composite monitor, where mode 0 disables the color burst, making all text appear in grayscale. Mode 1 enables the color burst, allowing for color. Mode 0 and Mode 1 are functionally identical on RGB monitors and on later adapters that emulate CGA without supporting composite color output. BIOS Modes 2 and 3 select 80 columns by 25 rows text modes, with each character still an 8×8 dot pattern, but displayed at

1560-432: A potentiometer labelled "BROWN ADJ." to adjust the amount of green signal reduction. This "RGBI with tweaked brown" palette was retained as the default palette of later PC graphics standards such as EGA and VGA , which can select colors from much larger gamuts, but default to these until reprogrammed. Later video cards/monitors in CGA emulation modes would approximate the colors with the following formula: which yields

1664-405: A raster display but does not generate the actual pixels , though it does contribute cursor and video-blanking information to the pixel video (intensity) signals. It is used to produce correctly timed horizontal and vertical sync and provide the address in memory from which the next pixel or set of pixels should be read. The process of reading that value, converting it into pixels, and sending it to

1768-399: A row of that character's graphic pattern. However, the 6845 left to the designer the freedom to route the bits of the memory and row addresses to video RAM as they saw fit. For this reason the word addressed by the 6845 does not have to equal one pixel or one character. In CGA alphanumeric (text) mode, there are two bytes per character, accessed sequentially by the 6845—the first byte is

1872-540: A television, and the 80 × 25 text and 640 × 200 graphics modes are intended for a monitor. CGA uses a 4-bit RGBI 16-color gamut , but not all colors are available at all times, depending on which graphics mode is being used. In the medium- and high-resolution modes, colors are stored at a lower bit depth and selected by fixed palette indexes, not direct selection from the full 16-color palette. When four bits are used (for low-resolution mode, or for programming color registers) they are arranged according to

1976-596: A time. Of course, before displaying, the CLUT has to be loaded with R, G, and B values that define the palette of colors required for each image to be rendered. Some video applications store such palettes in PAL files ( Age of Empires game, for example, uses over half-a-dozen ) and can combine CLUTs on screen. 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

2080-455: A total of 18 8-bit registers controlling all aspects of video timings. Only two addresses are exposed to external components - one to select which internal register is to be read or written to and another to access that register. register The 6845 is intended for character based displays. Every address it generates is composed of two parts - a 14 bit character address and a 5 bit row address. The character address increases linearly. When

2184-465: Is a display controller that was widely used in 8-bit computers during the 1980s. Originally intended for designs based on the Motorola 6800 CPU and given a related part number, it was more widely used alongside various other processors, and was most commonly found in machines based on the Zilog Z80 and MOS 6502 . The 6845 is not an entire display solution on its own; the chip's main function

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2288-436: Is a specialized RAM that stores R, G, and B values that define specific colors. Each color has its own address (index)—consider it as a descriptive reference number that provides that specific color when the image needs it. The content of the CLUT is much like a palette of colors. 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

2392-402: Is formed by the sum of two primary colors of equal intensity: cyan is green+blue, magenta is blue+red, and yellow is red+green. Every secondary color is the complement of one primary color: cyan complements red, magenta complements green, and yellow complements blue. When all the primary colors are mixed in equal intensities, the result is white. The RGB color model itself does not define what

2496-526: Is given by a gamma value of 1.0, but actual CRT nonlinearities have a gamma value around 2.0 to 2.5. 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). On a typical standard 2.2-gamma CRT display, an input intensity RGB value of (0.5, 0.5, 0.5) only outputs about 22% of full brightness (1.0, 1.0, 1.0), instead of 50%. To obtain

2600-422: Is given twice as many detectors as red and blue (ratio 1:2:1) in order to achieve higher luminance resolution than chrominance resolution. The sensor has a grid of red, green, and blue detectors arranged so that the first row is RGRGRGRG, the next is GBGBGBGB, and that sequence is repeated in subsequent rows. For every channel, missing pixels are obtained by interpolation in the demosaicing process to build up

2704-448: 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. 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 . The choice of primary colors is related to the physiology of the human eye ; good primaries are stimuli that maximize

2808-417: Is not a graphics mode, but a tweak of the 80 × 25 text mode. The character cell height register is changed to display only two lines per character cell instead of the normal eight lines. This quadruples the number of text rows displayed from 25 to 100. These "tightly squeezed" text characters are not full characters. The system only displays their top two lines of pixels (eight each) before moving on to

2912-491: Is not very popular as a video signal format; S-Video takes that spot in most non-European regions. However, almost all computer monitors around the world use RGB. A framebuffer is a digital device for computers which stores data in the so-called video memory (comprising an array of Video RAM or similar chips ). This data goes either to three digital-to-analog converters (DACs) (for analog monitors), one per primary color or directly to digital monitors. Driven by software ,

3016-484: Is one bit, providing two colors which can be chosen from the 16-color palette by programming hardware registers. In this mode, the video picture is stored as a simple bitmap, with one bit per pixel setting the color to "foreground" or "background". By default the colors are black and bright white, but the foreground color can be changed to any entry in the 16-color CGA palette. The background color cannot be changed from black on an original IBM CGA card. This mode disables

3120-468: Is one of the most common ways to encode color in computing, and several different digital representations are in use. 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 (2  − 1) to fit them into some bit groupings. Encodings of 1, 2, 4, 5, 8 and 16 bits per color are commonly found;

3224-461: Is provided which when triggered will duplicate and retain a copy of the video address so that it can later be read back by the CPU. This is useful for light pens and light guns which can function by sending a pulse to the 6845 when the electron beam passes, allowing a running program to read back the location that was pointed at. Because of this feature, most computer video adapters using a 6845 included

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3328-407: Is repeatedly read s times before the next line is read. This means that character displays using the 6845 require high memory bandwidth on the order of the bandwidth required for all-points-addressable graphics displays of the same resolution. A different video display controller that buffers one whole line of character data internally can avoid this repeated reading of each line of characters from

3432-448: Is represented by a cube using non-negative values within a 0–1 range, assigning black to the origin at the vertex (0, 0, 0), and with increasing intensity values running along the three axes up to white at the vertex (1, 1, 1), diagonally opposite black. An RGB triplet ( r , g , b ) represents the three-dimensional coordinate of the point of the given color within the cube or its faces or along its edges. This approach allows computations of

3536-558: Is the United Microelectronics Corporation (UMC) UM6845E CRT controller. During the time of cold war technology embargoes , the 6845 was cloned in Bulgaria under the designation CM607 . The 6845 was very similar and related to the later 6545 manufactured by MOS Technology (Commodore Semiconductor Group) and Rockwell (in two versions). The chip generates the signals necessary to interface with

3640-490: Is to properly time access to the display memory, and to calculate the memory address of the next portion to be drawn. Other circuitry in the machine then uses the address provided by the 6845 to fetch the pattern and then draw it. The implementation of that hardware is entirely up to the designer and varied widely among machines. The 6845 is intended for character displays, but could also be used for pixel-based graphics, with some clever programming. Among its better-known uses are

3744-1147: Is used. Following is the mathematical relationship between RGB space to HSI space (hue, saturation, and intensity: HSI color space ): I = R + G + B 3 S = 1 − 3 ( R + G + B ) min ( R , G , B ) H = cos − 1 ⁡ ( ( R − G ) + ( R − B ) 2 ( R − G ) 2 + ( R − B ) ( G − B ) ) assuming  G > B {\displaystyle {\begin{aligned}I&={\frac {R+G+B}{3}}\\S&=1\,-\,{\frac {3}{(R+G+B)}}\,\min(R,G,B)\\H&=\cos ^{-1}\left({\frac {(R-G)+(R-B)}{2{\sqrt {(R-G)^{2}+(R-B)(G-B)}}}}\right)\qquad {\text{assuming }}G>B\end{aligned}}} If B > G {\displaystyle B>G} , then H = 360 − H {\displaystyle H=360-H} . The RGB color model

3848-499: 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. Linear and nonlinear transformations are often dealt with via digital image processing. Representations with only 8 bits per component are considered sufficient if gamma correction

3952-753: The BBC Micro , Amstrad CPC , and Videx VideoTerm display cards for the Apple II . It is also part of many early graphics adapter cards for the IBM PC , including the MDA , Hercules Graphics Card (HGC), Color Graphics Adapter (CGA) and the Plantronics Colorplus . Its functionality was duplicated and extended by custom circuits in the EGA and VGA PC video adapters. Originally designed by Hitachi as

4056-449: The CPU (or other specialized chips) write the appropriate bytes into the video memory to define the image. Modern systems encode pixel color values by devoting eight bits to each of the R, G, and B components. 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. A CLUT

4160-612: The Enhanced Graphics Adapter (EGA) in 1984. The first manufacturer of a truecolor graphics card for PCs (the TARGA) was Truevision in 1987, but it was not until the arrival of the Video Graphics Array (VGA) 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. Actually, it had to wait

4264-576: The HD46505 , Hitachi-built versions are in a wide variety of Japanese computers, from Sony, Sharp, Panasonic, and Casio. Cloned later as MB89321A by Fujitsu. It is also known as the 6845 CRTC or the CRTC6845 , meaning " cathode-ray tube controller". This version was used on the Apricot PC and Victor 9000 to provide a 800x400 resolution monochrome display. A common clone of this CRT controller

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4368-582: The Jumbotron . Color printers , on the other hand, are not RGB devices, but subtractive color devices typically using the CMYK color model . 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). Each of the three beams is called a component of that color, and each of them can have an arbitrary intensity, from fully off to fully on, in

4472-497: The Numeric representations section below (24bits = 256 , each primary value of 8 bits with values of 0–255). With this system, 16,777,216 (256 or 2 ) discrete combinations of R, G, and B values are allowed, providing millions of different (though not necessarily distinguishable) hue, saturation and lightness shades. Increased shading has been implemented in various ways, some formats such as .png and .tga files among others using

4576-568: The RGBI color model: These four colour bits are then interpreted internally by the monitor, or converted to NTSC colours (see below). When using a direct-drive monitor, the four color bits are output directly to the DE-9 connector at the back of the card. Within the monitor, the four signals are interpreted to drive the red, green and blue color guns. With respect to the RGBI color model described above,

4680-456: The Rockwell 6545 lack interlaced output support and all 6545s include an optional address skew, which delays display enable for one character cycle if set. This second feature was incorporated into later variations of the Motorola 6845. The 6545 may be set to work in linear 14 bit mode using a status bit. On the 6845 the same thing requires adjustment of the character height. The 6845 reads

4784-410: 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 . When the intensities for all the components are the same, the result is a shade of gray, darker or lighter depending on the intensity. When the intensities are different,

4888-472: The 6845 and 6545. The biggest difference is that the 6545 may be configured so that it has sole access to the address bus for video memory. Two additional registers are included for setting any address the CPU wishes to read and the chip alternates between outputting addresses for display generation and the display set for CPU access. Smaller changes are that the MOS Technology and one variation of

4992-405: The 6845 imposes no limit on the size of each memory location that it addresses. If the word size is one byte, as is often the case, the 6845 can address 512 KiB . If the word size is 32 bits, e.g. for 32-bit color graphics with one pixel per word, then the 6845 can address 2048 KiB; for 64-bit words, it can address twice as much. These limits arise from the combination of the 6845 and the design of

5096-517: The 6845 is configured for a 2-pixel character height and the row address bit RA0 is used for bit 13 of the frame buffer address. This way, 200 vertical pixels can be used despite the 128 line limitation. Graphics mode on other systems used a similar trick: in the Hercules Graphics Card, bits 12-13 of the frame buffer address came from row address bits RA0-RA1, providing a vertical resolution of 348 pixels from 87 four-pixel-high "lines";

5200-462: The Amstrad CPC used a line height of 8 just like in text mode, mapping row address RA0-RA2 to memory address MA11-MA13 and character address CA0-CA10 to memory address MA0-MA10. These modes of operation were possible because the 6845 did not perform any buffering of character data. In the 1970s, 1980s, and to a lesser extent the 1990s, memory was expensive, fast memory was especially so, and this

5304-498: The CGA, but this was not available at release and would not be released until March 1983. Although IBM's own color display was not available, customers could either use the composite output (with an RF modulator if needed), or the direct-drive output with available third-party monitors that supported the RGBI format and scan rate. Some third-party displays lacked the intensity input, reducing the number of available colors to eight, and many also lacked IBM's unique circuitry which rendered

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5408-458: The RGB color model is described by indicating how much of each of the red, green, and blue is included. The color is expressed as an RGB triplet ( r , g , b ), each component of which can vary from zero to a defined maximum value. If all the components are at zero the result is black; if all are at maximum, the result is the brightest representable white. These ranges may be quantified in several different ways: For example, brightest saturated red

5512-425: 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 . Before the electronic age , the RGB color model already had a solid theory behind it, based in human perception of colors . RGB is a device-dependent color model: different devices detect or reproduce

5616-689: 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. However, the advantage is that an indexed-color image file can be significantly smaller than it would be with only 8 bits per pixel for each primary. Modern storage, however, is far less costly, greatly reducing the need to minimize image file size. By using an appropriate combination of red, green, and blue intensities, many colors can be displayed. Current typical display adapters use up to 24-bits of information for each pixel: 8-bit per component multiplied by three components (see

5720-674: The RS-170 and RS-343 standards for monochrome video. 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. This signal is known as RGBS (4 BNC / RCA terminated cables exist as well), but it is directly compatible with RGBHV used for computer monitors (usually carried on 15-pin cables terminated with 15-pin D-sub or 5 BNC connectors), which carries separate horizontal and vertical sync signals. Outside Europe, RGB

5824-434: The analogue green signal's amplitude. The exact amount of reduction differed between monitor models: the original IBM 5153 Personal Computer Color Display reduces the green signal's amplitude by about one third, while the IBM 5154 Enhanced Color Display internally converts all 4-bit RGBI color numbers to 6-bit ECD color numbers, which amounts to halving the green signal's amplitude. The Tandy CM-2, CM-4 and CM-11 monitors provide

5928-453: 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. The amount of this deviation is known as its gamma value ( γ {\displaystyle \gamma } ), the argument for a power law function, which closely describes this behavior. A linear response

6032-482: The canonical CGA palette: For the composite output, these four-bit color numbers are encoded by the CGA's onboard hardware into an NTSC-compatible signal fed to the card's RCA output jack. For cost reasons, this is not done using an RGB -to- YIQ converter as called for by the NTSC standard, but by a series of flip-flops and delay lines. Consequently, the hues seen are lacking in purity; notably, both cyan and yellow have

6136-568: The character and a "0" representing the background. These colors can be chosen independently, for each character on the screen, from the full 16-color CGA palette. The character set is defined by hardware code page 437 . The font bitmap data is only available to the card itself, it cannot be read by the CPU. In graphics modes, text output by the BIOS operates by copying text from the font ROM bit-by-bit to video memory. BIOS Modes 0 and 1 are both 40 columns by 25 rows text modes, with each character

6240-432: The chip signals horizontal sync it increases the row address. If the row address does not equal the programmatically set number of rows per character, then the character address is reset to the value it had at the beginning of the scan line that was just completed. Otherwise the row address is reset to zero and the memory address continues increasing linearly. This causes the same sequence of character values to be re-read from

6344-409: The color depth for the higher modes does not permit selecting freely from the full 16-color palette. The low-resolution 160 × 100 mode uses a 16-color palette and is set up as 80 × 25 character mode ( Mode 3 ) but uses memory-mapped graphics on 16 KB of memory. In the medium-resolution 320 × 200 modes ( Modes 4 and 5 ), each pixel is two bits, which select colors from

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6448-416: The common color component between them, e.g. green as the common component between yellow and cyan, red as the common component between magenta and yellow, and blue-violet as the common component between magenta and cyan. There is no color component among magenta, cyan and yellow, thus rendering a spectrum of zero intensity: black. Zero intensity for each component gives the darkest color (no light, considered

6552-445: The complete image. Also, other processes used to be applied in order to map the camera RGB measurements into a standard color space as sRGB. In computing, an image scanner is a device that optically scans images (printed text, handwriting, or an object) and converts it to a digital image which is transferred to a computer. Among other formats, flat, drum and film scanners exist, and most of them support RGB color. They can be considered

6656-426: The composite color burst signal by default. The BIOS does not provide an option to turn the color burst on in 640 × 200 mode, and the user must write directly to the mode control register to enable it. A number of official and unofficial features exist that can be exploited to achieve special effects. Some of these above tweaks can be combined. Examples can be found in several games. Technically, this mode

6760-418: 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. Gamma affects black-and-white TV as well as color. In standard color TV, broadcast signals are gamma corrected. In color television and video cameras manufactured before the 1990s, the incoming light was separated by prisms and filters into

6864-684: The cyan plate, and so on. Before the development of practical electronic TV, there were patents on mechanically scanned color systems as early as 1889 in Russia . The color TV pioneer John Logie Baird demonstrated the world's first RGB color transmission in 1928, and also the world's first color broadcast in 1938, in London . In his experiments, scanning and display were done mechanically by spinning colorized wheels. The Columbia Broadcasting System (CBS) began an experimental RGB field-sequential color system in 1940. Images were scanned electrically, but

6968-425: The dark-yellow color as brown, so any software which used brown would be displayed incorrectly. CGA offered several video modes. Graphics modes: Some software achieved greater color depth by utilizing artifact color when connected to a composite monitor. Text modes: IBM intended that CGA be compatible with a home television set. The 40 × 25 text and 320 × 200 graphics modes are usable with

7072-455: 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 . The normal three kinds of light-sensitive photoreceptor cells in the human eye (cone cells) respond most to yellow (long wavelength or L), green (medium or M), and violet (short or S) light (peak wavelengths near 570 nm, 540 nm and 440 nm, respectively ). The difference in

7176-524: The display buffer RAM, reducing the required memory bandwidth and allowing either slower, less expensive memory chips to be used, more time for a system CPU to access the memory, or a combination of both. Adding such a character buffer to the 6845 was deemed to not be cost-effective approach when the chip was introduced; however, only a few years later the VIC-II chip used on the Commodore 64 did include such

7280-411: The display of colors on a cathode-ray tube (CRT), liquid-crystal display (LCD), plasma display , or organic light emitting diode (OLED) display such as a television, a computer's monitor, or a large scale screen. Each pixel on the screen is built by driving three small and very close but still separated RGB light sources. At common viewing distance, the separate sources are indistinguishable, which

7384-402: The external memory connected to it, not from the 6845 alone. As described before, the 6845 cannot ordinarily provide large linear framebuffers . One design could only use 14-bit character addressing and set the number of lines per character to 1 but would be restricted to 128 lines and 16 KB of addressable memory. Although overwhelmingly compatible, a number of small variations exist between

7488-462: The eye interprets as a given solid color. All the pixels together arranged in the rectangular screen surface conforms the color image. During digital image processing each pixel can be represented in the computer memory or interface hardware (for example, a graphics card ) as binary values for the red, green, and blue color components. When properly managed, these values are converted into intensities or voltages via gamma correction to correct

7592-402: The foreground and background colors. Using either character 221 or 222, each half of each truncated character cell can thus be treated as an individual pixel—making 160 horizontal pixels available per line. Thus, 160 × 100 pixels at 16 colors, with an aspect ratio of 1:1.2, are possible. Although a roundabout way of achieving a 16-color graphics display, this works quite well and

7696-470: The fourth bit of the background color does not set intensity, but sets the blink attribute for the cell. All characters on the screen with this bit set will periodically blink, meaning their foreground color will be changed to their background color so the character becomes invisible. All characters blink in unison. By setting a hardware register, the blink feature can be disabled, restoring access to high-intensity background colors. All blinking characters on

7800-431: The image sensor, whereas older drum scanners use a photomultiplier tube as the image sensor. Early color film scanners used a halogen lamp and a three-color filter wheel, so three exposures were needed to scan a single color image. Due to heating problems, the worst of them being the potential destruction of the scanned film, this technology was later replaced by non-heating light sources such as color LEDs . A color in

7904-518: The inherent nonlinearity of some devices, such that the intended intensities are reproduced on the display. 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. RGB is also the term referring to a type of component video signal used in the video electronics industry. It consists of three signals—red, green, and blue—carried on three separate cables/pins. RGB signal formats are often based on modified versions of

8008-416: The intermediate optics, thereby reducing the size of home video cameras and eventually leading to the development of full camcorders . Current webcams and mobile phones with cameras are the most miniaturized commercial forms of such technology. Photographic digital cameras that use a CMOS or CCD image sensor often operate with some variation of the RGB model. In a Bayer filter arrangement, green

8112-444: The light under which we see them. In the additive model, if the resulting spectrum, e.g. of superposing three colors, is flat, white color is perceived by the human eye upon direct incidence on the retina. This is in stark contrast to the subtractive model, where the perceived resulting spectrum is what reflecting surfaces, such as dyed surfaces, emit. A dye filters out all colors but its own; two blended dyes filter out all colors but

8216-414: The medium and long wavelength cones of the retina, but not equally—the long-wavelength cells will respond more. The difference in the response can be detected by the brain, and this difference is the basis of our perception of orange. 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. Use of

8320-506: The memory for each raster line of each character row, before the 6845 advances the memory address to the next character row and repeats the same pattern. If the character address is used to look up a character reference in RAM and the row address to index a table of character graphics in ROM an ordinary text mode display is constructed. The character reference read from memory must be combined with

8424-511: The mixture. 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. 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

8528-536: The mode is even mentioned (although not explained) in IBM's official hardware documentation. This mode was used as early as 1983 on the game Moon Bugs . More detail can be achieved in this mode by using other characters, combining ASCII art with the aforesaid technique. This was explored by Macrocom, Inc on two games: Icon: Quest for the Ring (released in 1984) and The Seven Spirits of Ra (released in 1987). Motorola 6845 The Motorola 6845 , or MC6845 ,

8632-469: The monitor would translate the digital four-bit color number to some seven distinctive analog voltages in the range from 0.0 to 1.0 for each gun. Color 6 is treated specially; normally, color 6 would become dark yellow , as seen to the left, but in order to achieve a more pleasing brown tone, special circuitry in most RGBI monitors, starting with the IBM 5153 color display, makes an exception for color 6 and changes its hue from dark yellow to brown by reducing

8736-429: The next row. Character 221 of the CGA character set consists of a box occupying the entire left half of the character matrix. (Character 222 consists of a box occupying the entire right half.) Because each character can be assigned different foreground and background colors, it can be colored (for example) blue on the left (foreground color) and bright red on the right (background color). This can be reversed by swapping

8840-451: The other hand, the 6845 put the onus on its users to provide enough memory bandwidth to support rereading data on every line. If a character occupies one "word" in the video buffer, a display of l lines and c columns of characters with s scan lines per character requires l × c words of memory to represent a full screen of characters but takes s times that many memory accesses to complete one refresh cycle: each line of character words

8944-442: The play field) and one static (usually a status display). Vertical scrolling appears constrained because only the character start address can be set and the row address is always zeroed at frame start, but by adjusting border times it is possible to shift the position the framebuffer is shown on the raster display for increments in between whole characters. With drawing of blank pixels at the screen edges, this can be made invisible to

9048-634: The process of combining three color-filtered separate takes. To reproduce the color photograph, three matching projections over a screen in a dark room were necessary. The additive RGB model and variants such as orange–green–violet were also used in the Autochrome Lumière color plates and other screen-plate technologies such as the Joly color screen and the Paget process in the early twentieth century. Color photography by taking three separate plates

9152-469: The result is a colorized hue , more or less saturated depending on the difference of the strongest and weakest of the intensities of the primary colors employed. 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 ). A secondary color

9256-448: The row address to form the address for the character graphics ROM, with the character reference selecting a set of scan line patterns that forms one character and the row address indexing into that set to select one scan line. In other words, the ROM address is split into two parts in order to use the ROM as a two-dimensional array: the first dimension selects a character, and the second selects

9360-480: The screen blink in sync. The blinking attribute effect is enabled by default and the high-intensity background effect is disabled; disabling blinking is the only way to freely choose the latter eight-color indexes (8-15) for the background color. Notably, the GW-BASIC and Microsoft QBASIC programming languages included with MS-DOS supported all the text modes of the CGA with full color control, but did not provide

9464-405: The screen cannot be addressed directly. Instead, the screen is divided into a grid of character cells, each displaying a character defined in one of two bitmap fonts, "normal" and "thin," included in the card's ROM. The fonts are fixed and cannot be modified or selected from software, only by a jumper on the board itself. Fonts are stored as bitmaps at a color depth of 1-bit, with a "1" representing

9568-436: 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. As an example, suppose that light in the orange range of wavelengths (approximately 577 nm to 597 nm) enters the eye and strikes the retina. Light of these wavelengths would activate both

9672-405: The start address for its display once per frame . However, if the internal timing values on the chip are altered at the correct time it can be made to prepare for a new frame without ending the current one - creating a non-continuous break in generated addresses midway through the display. This is commonly used by demos and much more rarely games to provide one moving area of the display (usually

9776-448: 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. Color telephotographs were sent as three separated RGB filtered images consecutively. Currently available scanners typically use CCD or contact image sensor (CIS) as

9880-550: The system still used a moving part: the transparent RGB color wheel rotating at above 1,200 rpm in synchronism with the vertical scan. The camera and the cathode-ray tube (CRT) were both monochromatic . Color was provided by color wheels in the camera and the receiver. More recently, color wheels have been used in field-sequential projection TV receivers based on the Texas Instruments monochrome DLP imager. The modern RGB shadow mask technology for color CRT displays

9984-408: The text modes 0 and 2, Mode 5 disables the color burst to allow colors to appear in grayscale on composite monitor. However, unlike the text modes, this also affects the colors displayed on an RGBI monitor, altering them to the cyan/red/white palette seen above. This palette is not documented by IBM, but was used in some software. In the high-resolution 640 × 200 mode ( Mode 6 ), each pixel

10088-460: The three RGB primary colors feeding each color into a separate video camera tube (or pickup tube ). These tubes are a type of cathode-ray tube, not to be confused with that of CRT displays. With the arrival of commercially viable charge-coupled device (CCD) technology in the 1980s, first, the pickup tubes were replaced with this kind of sensor. Later, higher scale integration electronics was applied (mainly by Sony ), simplifying and even removing

10192-701: 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. The RGB color model is based on the Young–Helmholtz theory of trichromatic color vision , developed by Thomas Young and Hermann von Helmholtz in the early to mid-nineteenth century, and on James Clerk Maxwell 's color triangle that elaborated that theory ( c.  1860 ). The first experiments with RGB in early color photography were made in 1861 by Maxwell himself, and involved

10296-408: The total number of bits used for an RGB color is typically called the color depth . 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 . For the RGB model, this

10400-419: The user creating just the illusion of a smooth vertical scroll. RGB color model The RGB color model is an additive color model in which the red , green and blue primary colors of light are added together in various ways to reproduce a broad array of colors . The name of the model comes from the initials of the three additive primary colors , red, green, and blue. The main purpose of

10504-412: Was an important concern. In the 1970s and early to mid-1980s, chip circuit densities were not very high either, and putting an 80-byte or larger character buffer into a chip like the 6845 might have enlarged the chip die by 50-100%, in turn making it more expensive by a few times that factor due to the exponential growth of chip defect rates and the consequent decline of production yield with die size. On

10608-610: Was patented by Werner Flechsig in Germany in 1938. Personal computers of the late 1970s and early 1980s, such as the Apple II and VIC-20 , use composite video . The Commodore 64 and the Atari 8-bit computers use S-Video derivatives. IBM introduced a 16-color scheme (four bits—one bit each for red, green, blue, and intensity) with the Color Graphics Adapter (CGA) for its IBM PC in 1981, later improved with

10712-489: Was to combine row address and character address to provide linear scanlines within a non-linear buffer. This has the advantages of easier programming for non-character display and easy smooth horizontal scrolling but can impede smooth vertical scrolling. For example the IBM CGA graphics mode uses a word size of one byte, and each word represents four or eight pixels (in the medium- or high-resolution graphics modes respectively);

10816-521: Was used by other pioneers, such as the Russian Sergey Prokudin-Gorsky in the period 1909 through 1915. Such methods lasted until about 1960 using the expensive and extremely complex tri-color carbro Autotype process. When employed, the reproduction of prints from three-plate photos was done by dyes or pigments using the complementary CMY model, by simply using the negative plates of the filtered takes: reverse red gives

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