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67-579: The MBC-550 has much better video display possibilities than the CGA card (based on the HD46505 CRTC, providing a 3-bit RGB palette of 8 colors at 640 × 200 resolution, vs CGA's 4 colors at 320 × 200 or 2 colors at 640 × 200 ). Other resolutions, like 144 × 200 and 576 × 200 were possible. This display was not completely compatible with the IBM PC. The computer lacks a standard BIOS , having only

134-836: A PAL TV. Another example is Runaround II . On PAL versions of the Commodore 64 , the delay line in the monitor or TV which averages the color hue , but not the brightness, of consecutive screen lines can be used to create seven nonstandard colors by alternating screen lines showing two colors of identical brightness. This is used in the game Mayhem in Monsterland , released in 1993 by Apex Computer Productions , and in Parallaxian . TRS-80 Color Computer users in PAL countries only see green and purple stripes instead of solid red and blue colors. The ZX Spectrum resolution

201-604: A broadcast-quality signal, that would mean 910 pixel cycles per each line (as opposed to 858 as later standardized by the ITU-R Recommendation BT.601 ), with about 750 of them occupying the visible portion of the screen. With the stretched lines of these early computers, each line was actually 912 pixel cycles long, and only a portion of the visible area was used - 560 pixels in case of Apple II (although not individually addressable without an 80 column expansion card ), 640 in case of CGA. Each pixel could have one of

268-417: 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 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

335-524: 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, 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

402-515: 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

469-490: A handful of titles that used this graphics mode. These color differences can be simulated within Altirra-based emulators. All models with RF or composite output connected to televisions exhibited this effect while those such as the original Atari 800 or later XE series with built-in chroma/luma support additionally displayed images without artifacts when connected to a computer monitor with chroma/luma inputs such as

536-407: 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,

603-551: A minimal bootloader in ROM that accesses hardware directly to load a RAM-based BIOS. The diskette format ( FM rather than MFM ) used is not completely compatible with the IBM PC , but special software on an original PC or PC/XT (but not PC/AT ) can read and write the diskettes, and software expecting a standard 18.2 Hz clock interrupt has to be rewritten. The MBC-550 was also the computer for NRI training. Starting by building

670-560: 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

737-693: 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

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804-466: A problem with 80-column text. It is for this reason that each of the text and graphics modes described above exists twice: Once as the normal "color" version and once as a "monochrome" version. The "monochrome" version of each mode turns off the NTSC color decoding in the viewing monitor completely, resulting in a black-and-white picture, but also no color bleeding, hence, a sharper picture. On RGBI monitors,

871-461: A signal that is an approximation of the broadcast standard. In both the Apple II and the CGA, each line is elongated to full 228 cycles of the color subcarrier. This is within the tolerances of most displays, so the image is displayed clearly, but the pattern generated by solid colors becomes straight vertical stripes instead. Each horizontal position within any line has constant phase relationship to

938-483: Is a stub . You can help Misplaced Pages by expanding it . Color Graphics Adapter The Color Graphics Adapter ( CGA ), originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter , introduced in 1981, was IBM 's first color graphics card for the IBM PC and established a de facto computer display standard . The original IBM CGA graphics card was built around

1005-431: Is a technique commonly used to address several graphic modes of some 1970s and 1980s home computers . With some machines, when connected to an NTSC TV or monitor over composite video outputs, the video signal encoding allowed for extra colors to be displayed, by manipulating the pixel position on screen, not being limited by each machine's hardware color palette . This mode was used mainly for games, since it limits

1072-440: Is also present, but generates more limited colors. Depending on the exact PAL system used results will vary (if PAL-M or PAL-N are used, color artifacts similar to NTSC might be possible). Although related, artifact colors are not the same as horizontal blurring. Blurring is a general effect of using a composite connection, that simply creates new colors due to a mix of adjacent horizontal pixel values. The exact mix will depend on

1139-503: Is an effect of using a composite video connection , where new colors are created by averaging individual pixel values. This is mainly due to the limited bandwidth of luminance and specially chrominance on analog systems. Contrary to artifact colors that are arbitrary, these new colors are completely dependent on the original values of adjacent pixels. Horizontal blurring is more pronounced at higher display resolutions and when saturated colors are used (specially blue and red). This effect

1206-509: 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 the RGBI color model: These four colour bits are then interpreted internally by the monitor, or converted to NTSC colours (see below). When using

1273-670: Is limited and the results unreliable. The Apple II can be modified to output a 50 Hz signal for use in PAL and SECAM regions. However, when connected directly to a display, it results in a black and white picture. "Eurocolor" expansion cards were available that essentially decode NTSC artifacts and re-encode them as PAL or SECAM. Atari 8-bit machines are capable of generating artifact colors (red, yellow, violet and green) on monochrome modes taking advantage of PAL artifacts. A pinball table called Das Uboat , for Atari 800XL Pinball Construction Set , displays artifact colors when viewed on

1340-417: 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

1407-404: Is not possible to reliably display 256 dots across the screen due to the limitations of the NTSC signal and the phase relationship between the graphics chip clock and colorburst frequency. Using the first color set, alternating columns of green and black pixels are not distinct and appear as a muddy green color. However, switching to a white and black color set, instead of a muddy gray as expected,

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1474-484: 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

1541-464: 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 the analogue green signal's amplitude. The exact amount of reduction differed between monitor models:

1608-489: The Atari ST also have graphics prepared with dithering techniques to take advantage of composite TV connections. The Mega Drive/Genesis takes advantage of composite video horizontal blurring of vertical dither patterns to simulate transparency effects on many games. William Kier (the artist on Eternal Champions ) stated performing manual dither for the graphics on that game, and that it's likely most games dithered in

1675-659: The CoCo Max art package provides them in its palette of colors. The resulting 16 color palette is (approximate colors for illustration purposes only): The CoCo 3 fixes the clock-edge problem so it is always the same; the user holds the F1 key during reset to alternate the color set. On this computer games can be patched to use a new 128×192 four color mode provided by the Graphics Interrupt Memory Enhancer (GIME) chip, with hardware colors mapped to

1742-798: The Color Television Interface Adaptor (CTIA) chip displayed black or white images at a resolution of 320×192. Programmers quickly discovered that the odd or even patterns of adjacent black and white pixels in this mode would generate one of two additional colors (blue/brown or olive/pink) and software such as On-Line Systems ' The Wizard and the Princess used this side-effect to display up to four colors at maximum resolution. This technique and its technical underpinnings were documented in Appendix D of De Re Atari . Games such as Lode Runner , Flight Simulator II , and

1809-568: The Commodore 1701 . For some undocumented reason known only to Atari, they did not enable the chroma pin on the monitor jack of the 800XL although several modifications have been published to incorporate this support. Many first generation MSX computer games use horizontal blurring and dither to generate a palette of 125 simultaneous colors. Companies like Konami , Hal Laboratory or Ponyca used this technique regularly. Sony 's Graphic Master Lab paint program allowed these 125 colors to be used in user-created drawings. Home computers like

1876-534: 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 the CGA, but this was not available at release and would not be released until March 1983. Although IBM's own color display

1943-470: 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 a 4-bit digital ( TTL ) RGBI interface, such as

2010-474: The Ultima series took advantage of this effect to display extra colors. When Atari began shipping computers with the improved Graphic Television Interface Adaptor (GTIA), users found that such programs displayed incorrect colors and required an updated version of the software. In fact, artifact colors were inconsistent across the entire Atari 8-bit product line complicating playfield design but only affected

2077-435: The 128x192 four-color modes. Thus, the entire set of Extended Color BASIC graphics commands can be used with the artifact colors. Some users developed a set of 16 artifact colors using a 4×2 pixel matrix. Use of POKE commands also make these colors available to the graphics commands, although the colors have to be drawn one horizontal line at a time. Some interesting artworks were produced from these effects, especially since

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2144-456: The 1992 Amiga game Lionheart in order to create additional colors. The technique was also used frequently by British software house The Bitmap Brothers . The special Hold-And-Modify is particularly suited for displaying "high color" TV-like images, taking full advantage of horizontal blurring. Using a composite connection with the PAL TV system also generates new colors, but their number

2211-402: The 4 predefined phase relationships to the color burst, so a "fake" subcarrier that will be interpreted as color by the display, can be constructed by outputting specific pixel patterns. In case of adapters that also have native color capabilities, such as the CGA, this technique can be further expanded by forming patterns out of the built-in colors - this way, the "real" subcarrier generated by

2278-674: The 8088 in Japan as a second source , prompted by a widespread chip shortage at the time. As part of the agreement with Intel, Sanyo was not to sell their 8088 chips except as part of their Sanyo MBC-550 series computers. Soft Sector was a magazine for people who owned Sanyo MBC-550 and 555 DOS computers. (But much of the content equally applied to most IBM clones at the time.) A typical issue includes news, reviews, how-to's, technical advice and education, tips and tricks, as well as BASIC language programs that one could type in and adapt to suit one's needs. This computer-engineering -related article

2345-435: 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 a greenish tint, and color 6 again looks dark yellow instead of brown. The relative luminances of

2412-617: 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

2479-410: 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

2546-418: The color subcarrier under this system, so lighting up a pixel at each specific horizontal index always has the same effect on the color information as interpreted by the display. It is also typical for these types of display adapters to have pixel clocks that are a multiple of the NTSC subcarrier frequency. Both the Apple II and the CGA use the pixel clock of 14.318 MHz, four times the color subcarrier. For

2613-401: 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

2680-427: 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

2747-878: The computer, the NRI promised you would be "qualified to service and repair virtually every major brand of computer". NRI was advertised in Popular Mechanics and Popular Science throughout 1985. The MBC-550 is less PC compatible than the IBM PCjr . Its inability to use much PC software was a significant disadvantage; InfoWorld reported in August 1985 that Sanyo "has initiated a campaign to sell off" MBC-550 inventory. The company's newer computers were, an executive claimed, 99% PC compatible. Early MBC-500 machines used true Intel 8088 microprocessors. In late March 1984, Sanyo reached an agreement with Intel to manufacture

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2814-509: The display's effective horizontal resolution. It was most common on the IBM PC (with CGA graphics ), TRS-80 Color Computer , Apple II and Atari 8-bit computers , and used by the Ultima role-playing video games. Software titles (such as King's Quest for the IBM PC) usually provided an option to select between "RGB mode" and "Color Composite mode" . On PAL displays the effect

2881-399: The first game in the game series to be ported to IBM PC, uses CGA composite graphics. King's Quest I was also innovative in its use of 16-color graphics. Other titles include Microsoft Decathlon , King's Quest II and King's Quest III . The TRS-80 Color Computer (also known as Coco) two color 256×192 graphic mode allows the display of four colors by exploiting NTSC artifacts. It

2948-402: 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

3015-470: 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

3082-506: The hardware will interfere with the "fake" one residing within the pixel patterns, causing the display to interpret the result as new, unique colors. In the PAL system, the phase of the subcarrier is interpreted differently from line to line, and the phase of the color burst is strictly required to change on alternate lines. This makes the tricks described above infeasible. SECAM uses frequency modulation , so generating artifact colors would require timing far more precise than synchronizing

3149-456: The line frequency, i.e., each line contains 227.5 color subcarrier cycles. This causes the apparent phase of the subcarrier to be reversed every line, which results in solid colors being displayed as a checkerboard-like pattern when viewed on a monochrome display that does not filter out the color information. Computers such as the Apple II and the CGA video card for the IBM PC , output

3216-516: The maximum number of colors the CGA can display at the same time to 1024. This technique involves a text mode tweak which quadruples the number of text rows. Certain ASCII characters such as U and ‼ are then used to produce the necessary patterns, which result in non-dithered images with an effective resolution of 80×100 on a composite monitor. Many of the more high-profile game titles offers graphics optimized for composite color monitors. Ultima II ,

3283-550: 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). Composite artifact colors Composite artifact colors

3350-429: 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

3417-419: The offset of the pixels by half a pixel-width in relation to the color-burst signal. The high-resolution display offers more colors simply by compressing more, narrower pixels into each subcarrier cycle. The coarse, low-resolution graphics display mode works differently, as it can output a pattern of dots per pixel to offer more color options. These patterns are stored in the character generator ROM and replaces

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3484-464: 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 a potentiometer labelled "BROWN ADJ." to adjust the amount of green signal reduction. This "RGBI with tweaked brown" palette

3551-453: The pixel clock to the subcarrier frequency of either NTSC or PAL . For these reasons, artifact colors were generally only used with the NTSC color system. They are theoretically possible in any of them, due to the fact that in every analog television system, color information resides within the same bandwidth as luminance information. Artifact colors should not the confused with the more common horizontal blurring effect. Horizontal blurring

3618-576: The required values. Color graphics on the Apple II uses a quirk of the NTSC television signal standard, which made color display relatively easy and inexpensive to implement. The Apple II display provides two pixels per NTSC subcarrier cycle. When the color burst reference signal is on and the computer attached to a color display, it can display green by showing one alternating pattern of pixels, magenta with an opposite pattern of alternating pixels, and white by placing two pixels next to each other. Later, blue and orange became available by tweaking

3685-404: The result is either orange or blue. Reversing the order of the alternating dots will give the opposite color. In effect, the 256x192 two color mode becomes a 128×192 four color mode with black, orange, blue, and white available. Most CoCo games used this mode as it generates more useful colors than the ones provided by the native four color modes. The graphics chip internally can power up on either

3752-422: The result of cross-color artifacting, they are often called "artifact colors". Both the standard 320×200 four-color and the 640×200 color-on-black graphics modes could be used with this technique. Early efforts resulted on a usable resolution of 160×200 with 16 colors. Actual colors depend on the base palette and resolution used, as shown on the gallery below: Later demonstrations by enthusiasts have increased

3819-500: The rising or falling edge of the clock, so the bit patterns that represent orange and blue are not predictable. Most CoCo games start with a title screen and asks the user to press the reset button until the colors are correct. Readers of The Rainbow or HOT CoCo magazine learned that they can use some POKE commands to switch the Motorola 6847 graphics chip into one of the artifact modes, while Extended Color BASIC continues to operate as though it were still displaying one of

3886-455: The same fashion. This effect was used so widely used that it can be simulated on modern hardware clones like the Mega Sg . The Commodore Amiga, when connected over composite video, suffered from noticeable horizonal blurring, specially affecting colored pixels and smoothing out dithered transitions. This technique was used on most titles. Pixel artist Henk Nieborg mentions using dithering on

3953-523: The saturation and specific colors of the original pixels. Nevertheless, this effect can be exploited by using dither patterns, generating new intermediate palette colors on machines with a sufficiently high resolution display, like the ZX Spectrum , Mega Drive/Genesis , NES/Famicom or Amiga . In the NTSC color system as used in broadcasting, the color subcarrier frequency is exactly 227.5 times

4020-480: 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

4087-405: 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

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4154-542: The text character bit patterns when the computer is switched to low-res graphics mode. The text mode and low-res graphics mode uses the same memory region and the same circuitry is used for both. An example of full usage of artifact colors on the Apple II is the Dazzle Draw paint program. If seen in monochrome the image is composed of black and white vertical dither patterns, but when seen on NTSC colors appear. Graphics 8 mode on early Atari 8-bit computers with

4221-408: 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

4288-403: The two versions of each mode are identical, with the exception of the 320×200 graphics mode, where the "monochrome" version produces the third palette. However, programmers learned that this flaw could be turned into an asset, as distinct patterns of high-resolution dots would turn into consistent areas of solid colors, thus allowing the display of completely new colors. Since these new colors are

4355-403: Was exploited by game artists on some machines (specially those capable of generating higher resolution graphics but having a limited color palette) through the use of dithering patterns. When using IBM's Color Graphics Adapter (CGA) with a NTSC TV as a composite monitor , the separation between luminance and chrominance is imperfect, yielding cross-color artifacts. This is especially

4422-618: 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 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

4489-405: 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 the canonical CGA palette: For the composite output, these four-bit color numbers are encoded by

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