Sunday, March 26, 2023

IBM Composite Artifact Color Games and Related Topics

Top - Direct Colors Old CGA & New CGA
Bottom - High Resolution Artifact Colors Old CGA & New CGA

Back in 2013 I gave an overview of composite color usage on the IBM PC platform.  I included a list of all games I knew about or could find which supported composite color graphics.  Now, 10 years later, new information has made that list less than inaccurate and less than fully inclusive.  Let's talk about these games and give a new, more accurate list.  I will also talk about other topics related to CGA and color in more detail below.  

Before we begin, let me briefly define what I am talking about.  The IBM CGA card will show color from its composite video port with any game that uses the 320x200 pixel mode and either the cyan/magenta/white or green/red/brown palettes using IBM PC BIOS Mode 4.  It will also show color with 40-Column or 80-Column Text Modes using IBM PC BIOS Modes 1 and 3, respectively.

The IBM CGA has circuitry to tell an NTSC Color television or monitor directly what colors to display on a line, pixel by pixel, and for solid-colored graphics or graphics with double-wide pixels, you will see colors that more or less match what the RGB monitor would show.  This is what is called direct color and it is generally uninteresting as RGB monitors can display purer and truer colors with sharper text and graphical edges.  

The IBM CGA can also show composite colors using its 640x200 pixel mode which is based on a IBM PC BIOS mode, (Mode 6) but requires flipping a bit in the CGA's registers to turn the color burst on.  Without the color burst, this mode will appear in monochrome on both RGB and composite monitors, but with the burst on, the composite monitor will decode the video signal to show artifact color.  Comparatively speaking, on the Apple II all color, regardless of mode, is artifact color.

Some games rely on decoding quirks of the low color bandwidth versus the higher monochrome component of the NTSC video signal that results in the TV or monitor displaying color that should not be present.  These are called artifact colors and generally arise from a raw image in a pattern of columns of alternating white pixels with black or two colored pixels in a repeating pattern.  Instead of displaying as a broken series of pixels or lines of alternating colors as would be displayed on an RGB monitor, instead the artifacts result in new colors being displayed in a solid line for the length of the pattern.  

Artifact color can be shown in 320x200 color graphics mode alongside direct color.  Direct color pixels can be used to vary the color of artifact pixels.  This mode does not give quite as much detail or as strong color primaries as 640x200 graphics mode, but it was used on many games because the results could look acceptable on RGB monitors.  

Without further ado, the new list is here.

Statistics and Patterns (Tab 1)

Starting with the first tab of the spreadsheet, of the games I have found, 60 support 640-pixel composite color graphics, and all but one use light gray or white for the foreground color.  Of the 105 320-pixel composite color graphics games I found, all but 12 use a cyan/magenta white palette.  

Sierra On-line was quite the fan of composite artifact color graphics, so much so that 6 of the 8 games on this list which only support composite on their original release were published by Sierra.  Sierra was not consistent with its lack of RGB support, as some games from the same time period had RGB choices and others did not or RGB support was added in a later version.  Sierra's support for IBM CGA composite artifact color was strong, it usually used the 640x200 composite color mode to show a broader palette of colors compared to the 320x200 mode.

Top Level - Microsoft Decathlon Old CGA & New CGA
Bottom Level - Dragon Wars - Old CGA & New CGA

Old and New CGA

You might ask why do some 640x200 games use light gray and other games use white?  Similarly, why do some games use a low resolution palette and others the same palette in high resolution?  A theory is that those games using the less bright color choices developed their graphics with an old CGA card.  Old CGA cards were generally much brighter than new CGA cards, everything else being equal.  This must have been due in part because old CGA has a peak to peak voltage of 1.5v as opposed to the more common 1v peak to peak.  Less modern CRTs may tolerate this voltage more readily, but it will still result in brighter images.  There was at least one contemporary report of the older cards being incredibly bright.

Old CGA and New CGA only have a real distinction in the 320-pixel mode and in Pitstop 2.  In the 640-pixel mode with light gray or white (or dark gray) as the foreground "color", there is no direct color being generated.  While Old CGA and New CGA have color differences, especially in the red color, one can look like the other with an adjustment of the display's tint, brightness or contrast control.  Only when direct and artifact colors are mixed, which is the case in 320-pixel mode and for Pitstop 2, which uses a 640-pixel mode with a light green foreground color, do the differences between Old CGA and New CGA come to a head.  

Any game developed before 1984 had to be developed for the old CGA cards, IBM did not revise the CGA composite video circuit until 1984.  One of the major differences between old and new CGA is that new CGA feeds the luminance signal back into the color signal in order to allow for more shades of monochrome color to be distinguished on monochrome displays.  IBM added this feature for the IBM Portable PC, announced in February 1984, as it came with a built-in 9-inch amber composite monitor.  

Top - Maniac Mansion Composite New CGA & Hue-adjusted PCjr
Bottom - Turbo Champions RGB CGA & New CGA Composite

Minimal, Poor and Unintended Artifact Color (Tab 2)

Not all games on this list use artifact color to great effect.  Lode Runner and its sequel only use it sparingly.  Maniac Mansion's use is particularly poorly done.  Beneath Apple Manor's is barely noticeable.  The first Wolfenstein game only uses it on the title screen and the second barely uses it in-game.  Floppy Frenzy uses it only for a single graphic, although that graphic is shown often on every gameplay screen.

Some games were once considered to have artifact color support but really do not when you actually consider how their graphics worked.  Boulder Dash 1 and Turbo Champions' artifact color is only present by accident because the bits used for tile graphics are the same for both CGA and PCjr/Tandy. Boulder Dash 2 used Mode 5 for its graphics mode in all known releases, including its original standalone release from First Star Software, except in the Super Boulder Dash compilation, by which it is best known.  The Fourth Protocol can freely change the colors but has no obvious graphic patterns that would take advantage of artifact color.  Any games developed, programmed or ported by European or Brazilian developers, like The Fourth Protocol, are extremely unlikely to support artifact color intentionally because artifact color does not work with PAL video.  (PAL Artifact Video is something made up by emulators.)  I have put together a separate tab for games once claimed to support composite artifact color or give some false indication that they do but really do not.

Even if a game has questionable or debatable artifact color support, many people may prefer to run the game on a composite monitor.  Consider Questprobe: Featuring the Incredible Hulk, the game uses mostly double-wide pixels, which do not generate color artifacts in 320x200 mode.  However there is some subtle usage, as shown in the picture below, as the magenta dots give a pinker skin tone with composite.  Even if that were not present the RGB cyan color makes for a much more appropriate composite green color for the Hulk on old CGA.

Questprobe: Featuring the Incredible Hulk - RGB CGA and Old CGA Composite

Monitor Type Selection

Many but far from all CGA games will offer the user some ability to choose which graphics he or she wants to have displayed.  One option will be for composite color monitors and TVs.  Another will be for RGB Color displays.  Some will offer a third option for a monochrome display or black and white TV.  A game may present these options via a prompt at the initial bootup, in a menu that is accessed once the game is started, a command line argument, an in-game function key or even an installation program.

If you see a selection for composite and TV, it is the same selection,  Some black and white selections may be identical to  a color composite or TV option.  A monochrome or black and white selection is one of the few times that a CGA supporting program will intentionally display 640x200 monochrome graphics.  

Judging the Composite Support

Using DOSBox SVN's CGA emulation, one can easily see which mode a game is using by running composite color games with the DOSBox composite option off (F12 cycles through composite modes with the CGA machine type).  For 640-pixel games, the intent to use composite color is obvious.  640-pixel monochrome graphics were rarely used in games, (Jet 2.0's title screen is the kind of use you might have seen by the mid-80s) and almost never for a significant period of time.  

When it comes to 320-pixel modes, the only definite time a game will not support composite color is if it uses a cyan/red/white Mode 5 palette.  Mode 4 palettes always will show some color on a color composite display.  Developers preferred to use the cyan/magenta/white palettes because the colors were generally less garish and less likely to clash than the red/green/brown palettes.  Mode 4 graphics can be debated whether artifact color was intended in many games.  

Top - Ultima II PC version Old CGA
Bottom - Ultima II PCjr. version

Artifact Color on the PCjr. (Tab 3)

Despite the PCjr. possessing a 16-color 160x200 direct color graphics mode which had many advantages over CGA artifact color modes, artifact color was still used on the PCjr.  It is a surprisingly  complicated subject.  Games which use artifact color and were released before the PCjr.'s introduction will either show wrong artifact colors (usually in 320x200 games) or no artifact color (for some 640x200 games).  This assumes that the game works at all on the PCjr., and some games like Microsoft Decathlon do not. 

Games that use the 640x200 artifact color mode have to write directly to the CGA hardware registers, setting the video mode to Mode 6 with the PC or PCjr.'s BIOSes does not turn on the color burst signal needed to make a display show color.  The PCjr lacks the CGA's hardware registers and thus must use different registers to perform the same function.  Also, some games set the video mode to 640x200 directly via writing the CGA hardware registers, but this mode setting will fail on the PCjr and the result could be a 320-mode being used instead, which will give wrong artifact colors.  

Of the 14 known games to support PCjr. composite artifact color, only three use the 640x200 mode.  The 640x200 mode has the advantage of being able to show essentially the same colors for CGA, PCjr. or Tandy if the programmer adjusts the pixel patterns correctly for each system type.  More PCjr. games used the 320x200 pixel mode but that is because they were both PC/PCjr. releases or, in the case of Ultima II as shown above, the previously-released PC version used 320x200.  BC's Quest for Tires and Wizard of Id's WizType are unusual in that they use 320x200 artifact color on PCjr. whereas on PC they used 640x200.  In each game, the programmer modified the 4-color direct color palette from the default BIOS mode palettes.  

For four of these games on this list, their composite support is less-than-great by any reasonable standard, yet I put them in the PCjr. tab because they arguably look their best and look decent on a PCjr. and much better than an IBM CGA card in a PC.  

Top - Adventure in Serenia Base RGB CGA &Tandy Correct Artifact Color
Bottom - Adventure in Serenia Old CGA &Tandy Correct Direct Color

Tandy's Curious Indifference to Composite Artifact Color (Tab 4)

Despite the fact that Tandy shipped seven Tandy 1000 home computer models with support for composite video (1000/A/HD/EX/HX/SX/TX), its composite video implementation was rather poor in comparison to IBM's CGA or PCjr.  While Tandy 1000s will display direct colors more or less like an IBM CGA card, artifact colors will not be the same.  As all known artifact color-supporting games (except for three) only targeted CGA or PCjr. composite artifact color, the artifact colors shown on the Tandy 1000s will be wrong.  In the 640x200 mode games, Tandy colors are about as far away from IBM's colors as they could get.  You might be able to get the colors close to or even more or less correct with your Tint/Hue control depending on your TV or other device.  If IBM is at 0 degrees on an imaginary color wheel, then Tandy is at 120 degrees, so your device will need to be fairly generous in its hue-altering capabilities. 

Tandy Direct & Artifact Colors (normal tint assumed)

It is important to note that the tint/hue control on your TV, monitor or capture card affects all colors produced, both direct and artifact colors.  If your program uses any direct colors (such as Bruce Lee's title screen), those colors will look incorrect.  This is a bigger issue for 320x200 pixel mode games which use artifact color, as most use direct color as well.  The resulting artifact colors used in 320 mode will be affected by the direct colors being used to generate them.  So you might be able to get artifact colors correct with the tint control, but any direct colors will look incorrect.

When Tandy was publishing games from developers who has heavily invested in PC and PCjr. development like Sierra, Spinnaker Software and Electronic Arts in the first years of the Tandy 1000s, it never insisted that these developers adjust their graphic patterns to make the colors look appropriate for Tandy's machines.  However, when games supported Tandy enhanced graphics, they would almost invariably look better than CGA artifact color graphics.  It may be remarked that Tandy was always happy to sell you an inexpensive RGB monitor like the Tandy CM-4 or CM-5, so they may not have insisted on proper composite artifact colors because that would push the customers use their own TVs.  For one Christmas season they even offered a CM-5 for free with the sale of one model of Tandy 1000.

Top - CGA Direct "Colors" as Displayed on a B&W Monitor, Old CGA & New CGA
Bottom - CGA Direct "Colors" without Saturation, Old CGA & New CGA

Monochrome Composite CGA (Tab 5)

CGA was, as its name implied, intended to show color, but it also had monochrome capabilities.  You could connect a CGA card to a black and white 15KHz monitor or TV and see shades of brightness via its composite video output.  Old IBM CGA cards could only display six distinct levels of brightness with direct colors while newer IBM CGA cards and most clones can display sixteen.  If such a thing as a digital RGB monochrome 15KHz monitor existed, then you could see sixteen shades of whatever color the screen displayed regardless of whether your CGA card was old or new.  

Monochrome monitors offered much sharper text compared to a color composite monitor.  Scanlines tend to be more prominent on a monochrome display due to the lack of a shadow mask between the beam and the phosphors.  The IBM's Portable PC used small monochrome CRTs because they were much lighter and required much less circuitry than a color CRT.  IBM used a CGA card in the Portable connected to a composite amber monitor.  

The display on the Portable's screen may look a little odd due to the way a monochrome screen handles color video.  On the Portable's display what would appear as solid colors on an RGB display appears as a set of stripes on the monochrome display instead of solid shades of gray.  This is not an issue of poor video quality from the CGA card.  A monochrome display does not generally filter out the color signal, so the chroma dot patterns corresponding to a color can be seen.  The color signal is interpreted as luma by a typical black and white display and thus shows a dot pattern on parts of the scanline which would be shown as color on a color display.  The dot pattern displayed is determined by the phase of the color signal at a given point on the line.  Blacks. whites and grays will not show color dots because those parts of the scanline only use luma.  

IBM's usage of a monochrome composite video screen was far from unique, monochrome composite video displays were very popular in the 1980s as they were cheaper and lighter than color CRTs and good for text-only programs.  These monitors, often using green, amber or even bluish phosphors, had been used with the PCs since day one.  Most of these displays were just one step up from black and white TVs, so their low TV line counts caused blending of high resolution pixels.  PC games sometimes used the high resolution graphics mode to take advantage of this monitor effect, causing different pixel patterns to show varying level of brightness when they reached the display.  A black and white TV may be best for these games, as it is more likely to blend pixels are more solid shades than a better quality monitor.


  1. Oh my this takes me back. Remembering my PC/XT clone (from Microway) with a CGA adapter and amber 12” VDU. Good days!

  2. That would be hilarious if in the movies everyone had to say "trademark" after mentioning the Hulk.