The Search for Artifact Color on the Commodore 64

NTSC composite artifact color is something typically relegated to computers with off-the-shelf graphics hardware.  We associate it with the Apple II mainly, which used it in its high resolution modes.  TRS-80 Color Computer fans also know it very well, because it was the only color available in that computer line's graphics until the Model 3.  IBM PCs also used with more frequency than was commonly known in the early days in CGA graphics cards.  But Commodore didn't rely on off-the-shelf 74-series logic to drive its home computers' displays.  It had bought the MOS company and all its chip fabrication expertise.  Its computers used real graphics chips and they displayed real color.  They didn't need the composite tricks to get their graphics working and they didn't need boards devoted to graphics either.  But I have come across some information which suggests that the assumption that the Commodore 64 did not support composite artifact color may not be supportable.

Practical Issues with a Tandy 1400 LT Laptop Comptuer

Recently I acquired a Tandy 1400 LT Laptop computer, so as tradition seems to demand, I will talk about my impressions of the machine, tips on how to use it and mistakes to avoid.  The Tandy 1400 LT is Tandy's first IBM PC compatible laptop.  As the 1400 LT is so very much a mostly-improved clone of the IBM PC Convertible, it makes sense to compare the two products.

In April of 1986, IBM released the first PC compatible that could conceivably be called a laptop, the IBM PC Convertible Model 5140.  In 1988, Tandy released its own version of the PC laptop, the Tandy 1400 LT.  The Tandy machine had many notable improvements over the IBM machine :

Video Potpourri II

Sometimes, one needs to discuss related subjects that do not by themselves warrant a full blog entry.  Hence the video potpourri series, in which I can talk about aspects of display technology.

I.  Composite Artifact Color Emulation

Composite artifact color emulation has been around for a long time.  Unfortunately, in many cases it just isn't very good at trying to replicate the look of a composite monitor.  Simple schemes just assign a color arbitrarily to a group of two or four monochrome pixels.  Mainline SVN DOSBox tries to simulate CGA composite color as if it were a VGA mode.  The colors are reasonably accurate to the real IBM CGA cards, but the text color fringing is rather blocky.  There are custom builds that use filtering and 16-bit color to give a more subtle impression of the composite color, but it still looks much, much cleaner than the real image.  You can obtain a custom build with better composite color emulation here : http://www.vogons.org/viewtopic.php?f=41&t=12319&start=660#p501453

Video Potpourri

I am going to discuss a pair of video topics in this post which do not by themselves merit full blog entries on their own.  Each discussion will have a link to a Youtube video demonstrating the topic discussed.

I.  Hercules Graphics Tidbits

Someone remarked on the VOGONS forum that certain 16-color LucasArts SCUMM games, Indiana Jones and the Last Crusade: The Adventure Game and LOOM, do not support Hercules Graphics.  Earlier SCUMM games, Maniac Mansion and Zak McKracken and the Alien Mindbenders support Hercules Graphics in both their original and Enhanced releases.  The Secret of Monkey Island, which came immediately after LOOM, also supports Hercules Graphics in its original 16-color release.

The Case for Composite

The SNES and Genesis lead the pack of the 4th generation of video game consoles.  The common versions of these consoles can support RGB without any more effort than acquiring a cable and a monitor.  The Turbo Grafx 16 can be modded to support RGB.  But in this article I will demonstrate that RGB is not always the best choice for 4th generation graphics, at least when dealing NTSC composite video

1.  Sega Genesis

The Sega Genesis usually uses a 320x224 graphics mode.  Some games use a 256x224 mode.  The 320x224 mode's horizontal resolution is so great that not all the pixels can be fully resolved in a composite video signal on a standard TV.  There is frequent color fringing in thin-font text through the composite signal.  Additionally, with alternating colors,  you can obtain color artifacts to give graphics a transparent or blending effect.  This effect was used fairly often and works best with long alternating vertical lines.

Unfortunately, this effect is lost with an RGB monitor.  Compare the Genesis screenshots on this page for examples : http://www.chrismcovell.com/gotRGB/screenshots.html

Here are some examples from several Sega Genesis games.  For these screenshots I am using Kega Fusion v3.64, with the normal RGB output and a video capture of a real Sega Genesis Model 1 for composite video.  In each pair of Genesis screenshots, you will see the RGB first, then the composite.

Earthworm Jim is particularly ugly looking with RGB :

Note the edges of the mountains in the background :

The waterfalls of the Sonic series just don't look as convincing in RGB, composite video gives them a transparency effect :

Also, compare the fronds of the palm trees in Sonic 2 :

Some games use a checkerboard pattern that allows for dithering to give a transparency effect.  It is not quite as seamless on a composite monitor as the vertical stripes method, but gives a more acceptable picture on an RGB monitor.  Streets of Rage 2 uses the effect to simulate the characteristics of a studio spotlight during the nightclub stage :

The effect looks obvious with RGB, as do the color limitations in this title screen for Echo the Dolphin :

You can even see dithering being used in Street Fighter II, which uses a 256x224 mode, to smooth out the color gradient's in the carpet in this stage :

However, sometimes composite video can produce some very unsightly artifacts, as shown in the empty life bars of Castlevania Bloodlines :

2.  Super Nintendo

The Super Nintendo almost always uses a 256x224 graphics mode.  The Turbo Grafx 16 and CD typically used a similar mode but unlike the SNES could do a 320x224 mode.  Thus for games using these resolutions, artifact graphics are not typically available.  Even in these systems, shadows and smoke/fog do make some us of the less-than fine resolution of composite video :

However, late in the SNES's lifespan, Nintendo sought to improve the graphics quality of some of its games by creating 3D models of sprites and background tiles on advanced Silicon Graphics computers and then storing what was needed in a pre-rendered form on the cartridge.  Pictures of these graphics looked awesome on boxes and manuals and magazines.

Games with this look, like the Donkey Kong Country series, Killer Instinct, Super Mario RPG were very popular and helped extend the life of the SNES without a silly and expensive CD add-on.  When playing the game, they looked amazing back in the day.  However, when played through and emulator or to a lesser extent through RGB, the flaws cannot be denied.  The graphics have been so reduced in resolution from their SGI originals that they tend to look fuzzy, even with the perfection an emulator like higan 0.94 can provide :

Composite video can help hide the sharp edges from the down-conversion.  It is kind of like free anti-aliasing.

The SNES could do true transparency, but even so, dithering was sometimes used to provide something akin to free transparency.  The first screenshot, from Chrono Trigger, shows natural transparency by the light streaming in from the window :

The second screenshot, from Secret of Mana, shows true transparency with the water covering the rocks, and dithered transparency in the text box :

The final screenshot, from Mortal Kombat 3, shows a transparent effect with the life bars :

To give a flavor of more accurate dithering I used a composite capture device and real hardware (an early 2-chip PPU model revision).

Occasionally, Genesis-like artifacting does appear on the SNES.  Consider Kirby's Dream Land 3, which uses a 512x224 resolution.  The increased bandwidth of an RGB monitor can essentially resolve 512 pixels, but a composite monitor cannot, and the result is free transparency on the lower quality device.  Compare the following :

The first screenshot shows artifact graphics in the object partially covering Kirby, but you can see the gaps in between the lines.  The second screenshot shows the transparency effect you would see on a composite monitor.

The original model of the SNES is capable of S-Video output without modification, but you really begin to lose the transparent effects and forgiving qualities of composite video output.  In light of the successful development of HD Retrovision's component video cables for the SNES and Genesis, giving North American gamers the equivalent of RGB video out, this is a timely topic.

3.  Atari 5200 and 7800

Unlike the Atari 2600, the 5200 and 7800 support 320-pixel wide graphics modes.  The Atari 5200 uses the same hardware chips as the Atari 8-bit home computers.  Choplifter for the Atari 5200 was ported from the Atari 8-bit home computers, which was in turn ported from the Apple II.  All three versions use composite artifact color.  The Atari 5200 only has an RF connection, so unless you mod your system for S-Video (the Atari 800 has Separate Luma/Chroma on its video connector port), you will always see artifact color.  When Atari later released Choplifter for the XEGS, another Atari 8-bit home computer games console, it redid the graphics for a 160-pixel wide mode, eliminating artifact composite color.  Look here for more information : http://nerdlypleasures.blogspot.com/2013/09/the-overlooked-artifact-color.html

The Atari 7800 also had a 320-pixel wide mode that supported artifact color, but relatively few games supported it.  Its 160-pixel mode was much easier to use and supported more colors on the screen.  One of the few games that do support artifact colors on the 7800 is Tower Toppler, a.k.a. Nebulus a.k.a. Castelian.  This might have been because the game was being ported to the Atari 8-bit and XEGS and the Atari 7800 at the same time by the same programmer.  As explained here, the Atari 8-bit version was canceled : http://www.atariprotos.com/8bit/software/towertoppler/towertoppler.htm  The Atari 7800 only has RF output, so you will always see composite artifact colors when playing the game on a real, unmodded NTSC system.  Playing it on a PAL system will result in very stripey, sometimes monochrome graphics.  This video will show you what the graphics should look like :

https://www.youtube.com/watch?v=FA3SPS-RKDM

4.  Sega Master System

The Sega Master System does support composite artifact color after a fashion.  It uses a 256-pixel wide mode but unlike the NES, it does not use a fractional color pixels that give a 3-line staircase effect.  It also does not vary each frame by one pixel.  This has the effect of making artifact colors rather stable and vertical on the SMS but diagonal and shimmery on the NES.  Sometimes you can see this in games.  See here for more information : http://nerdlypleasures.blogspot.com/2016/07/video-potpourri.html

IBM PC Color Composite Graphics

In one of my recent posts, I discussed artifact color composite graphics as demonstrated by all computers which were intended to use them.  In this post, I want to focus on artifact color composite graphics as available on the IBM PC and compatible systems.

IBM PC CGA Color Composite Graphics

First, I would like to address some myths.  The first myth is that only a few games used composite color. Well over 100 games have been confirmed to use composite color.  The second myth is that virtually all of them used the 640x200 graphics mode.  In fact, many, many games used composite color, although many looked acceptable on an RGB monitor, and just as many games used 320x200 graphics mode and color composite graphics as those that used the 640x200 graphics mode.  Here are a list of games that are known to use composite artifact color graphics and the type of graphics they use :

Game Title	Composite Color Type
Adventure in Serenia	320
Agent USA	320
Alphabet Zoo	320
Ancient Art of War	320
Archon: The Light and the Dark	320
Battle of Antietam	320
BC's Quest for Tires	640
Below the Root	320
Beneath Apple Manor	320
Black Cauldron, The	640
Blue Angels: Formation Flight Simulation	640
Borrowed Time	320
Boulderdash	320
Boulderdash II	320
Bruce Lee	640
BurgerTime	640
Buzzard Bait	320
California Games	640
Championship Baseball	640
Championship Golf: The Great Courses of the World - Volume One: Pebble Beach	320
Chuck Yeager's Advanced Flight Trainer	640
Crossfire	320
Demon's Forge	320
Dino Eggs	320
Donald Duck's Playground	640
Drag Race Eliminator	320
Dragon Wars	320
Exodus : Ultima III	320
Fooblitzky	320
Football	640
Freddy's Rescue Roundup	320
Frogger II: Three Deep	640
Gamma Force in Pit of a Thousand Screams	320
Gertrude's Puzzles	320
Gertrude's Secrets	320
Gettysburg: The Turning Point	320
Gold Rush	640
Indianapolis 500: The Simulation	640
J-Bird	640
Jumpman	640
Jungle Hunt	320
King's Quest	640
King's Quest II : Romancing the Throne	640
King's Quest III : To Heir is Human	640
King's Quest IV : The Perils of Rosella (AGI)	640
Lane Mastodon vs. the Blubbermen	320
Leisure Suit Larry in the Land of the Lounge Lizards	640
Lost Tomb	320
M.U.L.E.	320
Manhunter : New York	640
Manhunter 2 : San Francisco	640
Maniac Mansion (Low-Res)	320
MasterType	320
Mean 18	640
Mickey's Space Adventure	640
MicroLeague Baseball	320
MicroLeague Baseball II	320
Microsoft Decathlon	320
Microsoft Flight Simulator (v1.0)	640
Microsoft Flight Simulator (v2.0)	640
Mindshadow	320
Mixed-Up Mother Goose	640
Mr. Cool	320
Ms. Pac-Man	640
Murder on the Zinderneuf	320
Night Mission Pinball	640
Night Mission Pinball (v3.0)	640
Oil's Well	640
Pits & Stones	?
Pitstop II	640
Roadwar 2000	320
Roadwar Europa	320
Robot Odyssey	320
Rocky's Boots	320
Shamus	320
Sierra Championship Boxing	320
Solo Flight	320
Space Quest : Chapter I : The Sarien Encounter	640
Space Quest II : Vohaul's Revenge	640
Spy Hunter	320
Starflight	640
Strip Poker: A Sizzling Game of Chance	320
Sub Mission	320
Super Zaxxon	640
Superbowl Sunday	640
Tales of the Unknown: Volume I - The Bard's Tale	640
Tapper	640
Tass Times in Tonetown	320
The Bard's Tale II: The Destiny Knight	640
The Bard's Tale III: Thief of Fate	640
The Fourth Protocol	320
The Oregon Trail	320
The Seven Cities of Gold	640
The Tracer Sanction	320
The World's Greatest Baseball Game	640
Think Quick!	320
Transylvania	320
Troll's Tale	640
Ultima II : Revenge of the Enchantress	320
Ultima IV : Quest of the Avatar	320
Ulysses and the Golden Fleece	320
Wasteland	640
Where in the U.S.A. is Carmen Sandiego?	320
Where in the World is Carmen Sandiego?	320
Wilderness: A Survival Adventure	320
Winnie the Pooh in the Hundred Acre Wood	640
Wizard of Id's WizType	640
Zak McKracken and the Alien Mindbenders (Low-Res)	320
ZorkQuest: Assault on Egreth Castle	320
ZorkQuest: The Crystal of Doom	320

The advantage to using the 640x200 graphics mode is that a good color palette is available using white as the foreground color.  White or light gray, rather than high intensity or bright white was used because the brightness level was more tolerable on composite devices.  The disadvantages are that the game must support two completely different sets of graphics, otherwise users of RGB monitors would feel left out. Additionally, most games used an algorithm that requires extra coding and CPU time to implement for either the RGB or color composite mode.

The advantage to using 320x200 graphics is that only one set of graphics, or in a few cases two sets of very similar graphics, need be used.  Both users of composite monitors and RGB monitors can be satisfied, although the result may not be as impressive as tailoring graphics to either RGB or composite monitors.  The disadvantage is that the graphics designer has to cope with both direct and artifact colors, often giving a fuzzy image.  With the green/red/brown palette, the results often look somewhat garish and it was seldom intended to be used for composite color graphics.  Often that palette, many times with a blue background, would be used for the RGB graphics selection.  The colors choices available in the 320x200 modes are not as flexible as they would be in the 640x200 mode.

320x200 Palette 1 High Intensity Composite Color Graphics from L to R : RGB, Old CGA, New CGA, PCjr., Tandy

320x200 Palette 0 High Intensity Composite Color Graphics from L to R : RGB, Old CGA, New CGA, PCjr., Tandy

The above palettes do not quite give the full array of color combinations which the CGA card is capable. Although the palette choices in the 320x200 modes are limited, the background & border color can be freely selected from the full 16 colors which the CGA can display.  Similarly, the foreground color in the 640x200 mode can be set to any of the 16 colors CGA can display.  These color choices will affect the resulting artifact colors available.

640x200 Color Composite Graphics from L to R : Old CGA, New CGA, PCjr., Tandy

While color composite graphics may appear to be one way to display graphics, in reality there are three major types of color composite graphics.  First there are those generated by the IBM PC Color/Graphics Display Adapter and 100% compatible adapters.  Within this type there are two subtypes, early cards and late cards with minor differences between them.  Second, there are those generated by the IBM PCjr.  Third, there are those generated by the Tandy 1000 computers.

IBM CGA cards, Catalog Part Number 1504910 come with Card and PCB numbers

Card           PCB
1804456
1804464
1804472
1501486     1501453
1501981     1501982
6278550     6133807?
6447058

Cards 1804456 to 1501486 are early CGA cards.  1501981 to 6447058 re late CGA cards. The 180xxxx cards have the black brackets on them which the very earliest IBM PC cards had.  Later cards use a silver bracket appropriate for an IBM PC, XT or any compatible machine.  The major physical differences between the two versions of these can be seen here :

Old CGA vs. New CGA, note the increased number of resistors on the New CGA card (courtesy of minuszerodegrees.net)

An old CGA card will have either 7, 8 or 12 resistors, a new CGA card will have 15.  Note also in the above photo that the old card has a Motorola MC6845 and the new card has a Hitachi HD6845.  While the two work identically for typical software, demos may require one or the other.  The party-version of the 8088MPH demo only looks correct with an MC6845.  The final version looks correct with either chip.

Old cards seem to come exclusively with MC6845s, while new cards will use either chip.  Old cards always seem to use a green PCB color, but new cards almost always use a brown PCB color.

One of the chief differences between these cards is the number of shades of gray it can produce when connected to a monochrome composite monitor or B&W TV set through an RF modulator.  Old cards can produce two shades of gray plus black, while new cards can produce 15 shades of gray plus black in black and white modes.  Many computer users had to use monochrome green, amber or white monitors back in the day, and the increase in shades of gray meant that more detail could be seen in the graphics.  With the old cards, you had black for black and gray, white for white and bright white and gray for all other colors.  This is found in CGA Mode 5, which on an RGB monitor gives a cyan, red and white palette but on a color composite monitor will give either black and white (2 colors) or black, dark gray, light gray and white (4 colors).

Colorwise, new CGA was adjusted to more closely adhere to the NTSC standard.  It will appear more consistently across different monitors than old CGA.  There are differences between the saturation and brightness between the colors output by old and new CGA.  Newer monitors may make the image too dark with old CGA, requiring the user to increase the brightness level of his monitor.  There is a test program that can tell you which type of CGA card you may have.  Here are the screenshots of it showing how it informs you of the type you may have :

Old CGA has a raster bendiness issue with certain computers, and the black and white modes may not always eliminate all colors.  Running the signal through a powered RF modulator like the Recoton Video RF Modulator V647 should eliminate the bendy horizontal sections of the picture without reducing the video quality (assuming you are not modulating an audio signal with the video.)

Unlike the Apple II, where the pixels being output in the high resolution and double high resolution modes were either white or black, on the PC the pixels being put out have direct color.  The six colors in between black and white, without accounting for intensity, are generated by adjusting the phase of the 3.58MHz color burst signal for the hue and the amplitude of that signal for the brightness.  Unlike on an RGB TTL monitors from IBM, color #6 is dark yellow, not brown, because a color composite monitor or TV does not have circuitry built inside it to detect color #6 and turn it to brown.

For direct or chroma colors, both the old and new CGA cards look similar to the RGB colors, but there are minor differences between them.  The PCjr. and Tandy 1000 show direct or chroma colors identically with the new CGA cards.  Here are the 16 direct or chroma colors :

Rows 1 & 4 : RGB CGA Colors, Rows 2 & 5 : Old CGA Direct Colors, Rows 2 & 6 : New CGA, Tandy and PCjr. Direct Colors

For at least two games, Microsoft Decathlon and Championship Golf, the earlier card makes it much easier to read text than the later card.  Championship Golf may require the brightness controls to be turned down on the monitor.  Other games designed for old CGA are Sorcerer of Claymorgue Castle. Tournament Tennis, Quadrel and Willow look better with new CGA.

320x200 Palette 1 Color Composite Graphics Example - Adventure in Serenia New CGA

Some games like Donkey Kong, Boulderdash II, I, Damiano: The Wizard of Partestrada and Turbo Champions look like they support color composite graphics due to the vertical striped pattern graphics seen in some screens or tiles, but they really do an overall poor job on a color composite monitor. It is suspected that the ports did not convert the graphics with a great deal of thought.

320x200 Palette 0 Color Composite Graphics Example - Jungle Hunt (Note the Diving Bar, New CGA)

Pitfall 2 is an interesting piece of software when it comes to color composite mode support.  If you press 1 at the text screen, you will see 640x200 graphics with green as the foreground color on an RGB monitor.  I know of no game other than this that uses any foreground color other than white for 640x200 color composite graphics.  Obviously, this gives the graphics a greenish hue on a color composite monitor.  If you press 2 at the text readability screen, you will get 320x200 graphics with intense palette 0.  However, the road and the mountains have vertical stripes, which suggest that this mode is also intended to be used with a color composite monitor.  However, the stripes are there as a crude dithering effect, as using this mode on a color composite monitor makes the text very difficult to read.  The Fourth Protocol allows the user full control over the CGA card, and has a stripey pattern for 640x200 graphics that make them look tolerable with a color composite monitor.  It may be limited to the title screen, however, because the in-game graphics appear to always be 320x200, with the pixels doubled in a 640x200 mode.

640x200 Color Composite Graphics Example #1 - Pitstop II, New CGA

Color composite graphics were not limited to booters.  Sierra supported it in every AGI engine game it released, from King's Quest to Manhunter II : San Francisco.  Interplay supported it in The Bard's Tale 1-3, Dragon Wars and Wasteland.  No doubt their Apple II origins contributed to this.  Interestingly, in Wasteland you must select the graphics adapter in the install program, which then converts the graphics from 16-color to composite color as it installs.  To use another graphics adapter, you have to reinstall the game.  Considering its support for every other type of graphics adapter on the market, the color composite support in Lucasarts' Maniac Mansion and Zak McKracken is uncharacteristically poor.

640x200 Color Composite Graphics Example #2, - King's Quest, Old CGA

Tandy 1000 Composite Color Graphics

Tandy can only show the same direct or chroma colors as CGA, but the Tandy 1000 artifact colors are different.  Changing the hue adjust will be sufficient to change Tandy colors to late CGA colors in DOSBox, and vice versa, but only in the 640x200 mode.  A hue adjustment in the 640x200 mode of 120 degrees will give a good Tandy palette.  You can only approximate the palette colors for the 320x200 modes.  Games that are not "Tandy-aware" with their color composite graphics will show different colors. This occurs either with either 320x200 or 640x200 graphics.

Blue Angels: Formation Flight Simulation is the only game known where the color composite graphics look correct on the Tandy 1000 but do not look right on the IBM CGA cards.  It also apparently was developed on a system with a comb filter.  For a 1989 game, this would not have been difficult to find, but comb filters were not used on the composite color monitor and TVs of the early 1980s when most of the composite color CGA games were developed.  Many early 1980s games look better on monitors without comb filters.  Compare these two screenshots :

IBM CGA Composite

Tandy 1000 Composite

In the Tandy extended modes 160x200x16, 320x200x16 and 640x200x4, you will see color on a color composite monitor or TV.  In the 160x200x16 mode, there is no real artifact color since the pixel clock and the color burst frequencies are the same, 3.58MHz.  The graphics look blocky in this mode, but reasonably sharp.  Maniac Mansion on the Tandy 1000, using the Tandy graphics setting, would look very similar to how it looks on the Commodore 64, although there are color differences and the text is blockier.

Indianapolis 500 specifically supported both IBM and Tandy color composite graphics with different command line arguments so that the colors would look correct regardless of system.  However, the colors in each mode are not identical.  The command line switch /c1 will give colors appropriate for a CGA card, and switch /c2 will give colors appropriate for a Tandy graphics adapter.

Indianapolis 500 - The Simulation 640x200 RGB CGA

Indianapolis 500 - The Simulation 640x200 RGB Tandy

Indianapolis 500 - The Simulation Color Composite Early CGA

Indianapolis 500 - The Simulation Color Composite Late CGA

In modes using true 320x200 graphics (the AGI games use the 320x200 16 color graphics mode, but the effective graphics resolution is 160x200, at least for graphics above the command line), you can see color, but detail is lost, unintended artifacts that look like Hanover bars appear, and the game usually looks bad.  As far as 640x200x4 graphics go, no game is known to use that graphics mode.

Indianapolis 500 - The Simulation Color Composite Tandy (Simulated)

On a monochrome composite monitors or B&W TV sets, 16 shades of gray are always visible with Tandy 1000 or PCjrs.

IBM PCjr. Color Composite Graphics

The PCjr. does support color composite artifact colors, but the artifact colors are different from the CGA cards and the Tandy 1000.  Again this is due not to differences in the phase of the color burst but the pixel clock delay compared with the CGA cards.  In the 320x200 mode, there is a pixel clock delay of 120 degrees compared with the CGA cards.  PCjr. color composite graphics can appear quite different to CGA color composite graphics.

Below the Root sounds best (at least the opening song does) when run on an IBM PCjr. and the direct colors when the game is run on a PCjr. were tweaked to look very appropriate for a color composite monitor with artifact color.  Ditto for The Seven Cities of Gold, except it uses 640x200-based color composite graphics.

IBM PC CGA RGB

IBM PCjr. RGB

IBM PC CGA Old Composite

IBM PC CGA New Composite

IBM PCjr Composite

As explained in the prior blog entry, the PCjr's default 320x200 palette is not identical to the CGA's default cyan, magenta and white palette.  The PCjr. intentionally uses high intensity white instead, causing brightness and saturation differences.

Below the Root 320x200 Color Composite Late CGA

Below the Root 320x200 Color Composite Early CGA

Below the Root 320x200 Color Composite PCjr.

Wilderness : A Survival Adventure may show the best composite color results using the PCjr., but the underlying patterns are not changed for the machine.  Frogger II is PCjr. aware and shows good composite or RGB colors either with CGA or PCjr.  A late version of Pitstop II has direct support for the PCjr.'s 160x200x16 mode, so it will always look better than the CGA with or without color composite graphics.  Ditto for Murder on the Zinderneuf, all versions use 160x200x16 on the PCjr.  Several other games just use 160x200x16 on the PCjr. because it looks excellent on an RGB or color composite monitor.

BC's Quest for Tires uses 320x200 composite color graphics on the PCjr. but 640x200 composite color graphics on the PC.  Microsoft Flight Simulator 2.xx uses 640x200 composite color graphics for the PC and PCjr., but the patterns are different for each.  There was a version of Ultima II for the PCjr. that uses appropriate composite color 320x200 graphics.  M.U.L.E. also uses 320x200 composite color graphics.

Current SVNs of DOSBox emulate old and new CGA with the cga machine type, 640x200 and 320x200 color composite graphics but does not emulate color composite graphics with the tandy or pcjr machine types.

Other computers may have inaccurate CGA artifact colors.  The Columbia Data Products 1600 (one of the very first PC clones) came with a CGA clone card that is almost as off as the Tandy or PCjr.  A hue adjustment of 315 degrees will get something like its palette in 640x200 mode.  Here are the games that intentionally support composite color on an IBM PCjr. with the type of composite color they use :

Game Title	Composite Color Type
BC's Quest for Tires	320
Below the Root	320
M.U.L.E.	320
Ultima II : Revenge of the Enchantress PCjr. Version	320
Frogger II: Three Deep	640
Microsoft Flight Simulator (v2.0)	640
The Seven Cities of Gold	640

Lode Runner : Support for All Composite Color Types

Lode Runner for the PC always looks best in composite color mode, despite using the 320x200 resolution. Only the in-game border and certain objects on the screen really take advantage of composite color, but the solid objects always look appropriate regardless of monitor.

When first released for the PC, the game only supported the IBM PC and CGA.  A second release added PCjr. support by adjusting the patterns for the composite color objects.  A final release under the Tandy label retained the PC and PCjr.'s respective patterns but adjusted the patterns again when it detected a Tandy 1000 machine.  Here are correct screenshots for the CGA, PCjr. and Tandy both in RGB and Composite :

IBM PC CGA RGB

IBM PC Old CGA Composite

IBM PC New CGA Composite

IBM PCjr RGB

IBM PCjr Composite

Tandy 1000 RGB

Tandy 1000 Composite

Limitations of the Tint Control

NTSC color TVs and monitors have a tint (hue) control dial, buttons or function.  The tint control is intended to adjust for phase errors in a transmitted broadcast signal.  The tint control adjusts the phase of the TV's reference color burst signal slightly toward the green or red end of the spectrum.  The color burst is intended to have a phase of 180 degrees, and by using the tint control, you can adjust the TV's phase by about 40 degrees from the official phase.  This was important during the era of broadcast TV before cable became ubiquitous.  Here is an NTSC color wheel to give you an idea of where the colors fall by degrees :

Unfortunately, for Tandy and PCjr. display adapters, 40 degrees is not sufficient to turn Tandy or PCjr composite colors into CGA colors.  Relative to late CGA, assuming its color burst is near 180 degrees, 640x200 Tandy is at 300 degrees and 640x200 PCjr. is at 120 degrees.  In the 640x200 mode, you can get somewhat close to the CGA colors at the extreme end of the tint control (green for PCjr, red for Tandy), but in 320x200 mode, you really won't.  In DOSBox, F11 and Alt F11 emulate the function of the tint control.

This blog entry gives a very readable overview of how composite CGA works : http://8088mph.blogspot.com/2015/04/cga-in-1024-colors-new-mode-illustrated.html