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

The PCjr. and CGA Compatibility

When IBM designed the PCjr., it based it on its pre-existing IBM PC Color/Graphics Display Adapter (CGA).  However, IBM did not design it in a way that it would be guaranteed to be backwards compatible with all CGA software, especially games.  This article will demonstrate the limitations of the PCjr. with CGA games.

There are four types of games of CGA games, first those that are not aware of the PCjr (Adventure in Serenia), second those that are aware of the PCjr. but do not use the enhanced graphics features of the PCjr. (M.U.L.E.), third those that are aware of the PCjr. and enhance the graphics in some way (Alley Cat), and fourth those that do not really work on the PCjr. (Microsoft Decathlon).  (Interestingly, all these games were released by IBM).  This article is only concerned with the first two types of games.

CGA and the PCjr. are fully compatible at the BIOS level, but only partially compatible at the register level.  The PCjr. can do everything that CGA can do at the hardware level, it just has to do some things very differently.  The CGA is a relatively simple device with eight registers :

Hex Address       Register Function
3D4                    6845 Index Register (to access 18 internal registers)
3D5                    6845 Data Register
3D8                    Mode Control Register
3D9                    Color Select Register
3DA                   Status Register
3DB                   Clear Light Pen Latch
3DC                   Preset Light Pen Latch

IBM implemented all these registers except for the 6-bit Mode Control and Color Select Registers.  There is nothing present at 3D8 and 3D9 in the PCjr.  The CGA and PCjr. have true Motorola MC6845 CRTCs.  The PCjr. also has a video gate array that acts as the graphics controller.

In addition, the graphics memory window with CGA, B8000-BBFFF will also be found with the PCjr., regardless of the amount of memory the PCjr. has (since it shares its video memory with the CPU).

1.  What works

Anything that access the BIOS will work correctly in either the IBM PC with CGA or PCjr.  The PC BIOS through Int 10H, offers several video functions.  All the video functions in the PC are present on the PCjr. Among the chief functions of BIOS Int 10H include setting the graphics modes.  IBM defined seven modes in the BIOS for CGA, 0-6, as shown below

Mode 0 - 40 column x 25 line Text Color/Black and White
Mode 1 - 40 column x 25 line Text Color/Color
Mode 2 - 80 column x 25 line Text Color/Black and White
Mode 3 - 80 column x 25 line Text Color/Color
Mode 4 - 320x200 Graphics 4-Color
Mode 5 - 320x200 Graphics 4-Color/Black and White
Mode 6 - 640x200 Graphics Black and White

On an RGB monitor, all modes except 6 are color capable through the BIOS.  On a color composite monitor or TV, only Modes 1, 3 and 4 are capable of color.  IBM preferred the black and white modes so that text would appear legible on a color composite monitor or TV.

Two other important functions that Int 10H provides include setting the palette to either green/red/brown or cyan/magenta/white and setting the background + border color in the 320x200 graphics modes and the border color in the text modes.  Even though the register write is the same, it will not set the foreground color in the 640x200 mode.

Additionally, those tweaked text modes, found in games like Round 42 (160x100) or ICON : Quest for the Ring (320x200), may also work because the program tweaks the registers of the Motorola MC6845 CRTC.  ICON has a PCjr. executable, and some games like Styx had a PCjr. specific version.

2.  What doesn't work

Since the Mode Control Register does not exist in the PCjr., a program must select the modes using the BIOS.  Any program writing to the Mode Control Register to change its mode will not work.  In addition, for text modes CGA uses bit 5 to turn blinking off and allow a text cell to select the 8 intense colors.  Finally, when bit 2 is 0 it turns on color for the color composite mode.  This is the way that color composite graphics are shown on CGA using the 640x200 mode and the bit is 0 by default in Modes 1, 3 and 4.

The Color Select Register also does not exist in the PCjr., so any program that uses the register to select colors will not work.  Color selection in CGA is limited as follows :

For text modes, bits 0-3 selects the border color.
For 320x200 graphics modes, bits 0-3 select the background and border color.
For 640x200 graphics mode, bits 0-3 select the foreground color (background and border color is always black, works with color composite graphics when bit 2 of the Mode Control register is 0)

None of those functions will work at all on the PCjr.

Bit 5 selects the 3-color palette in 320x200 Mode 4.  If the bit is 0, then the palette is green, red and brown.  If the bit is 1, the palette is cyan, magenta and white.  This is the default.  In Mode 5, this bit has no effect, the palette is always cyan, red and white.  The background color is the only color that is freely selectable in the 320x200 modes.  Since bit 5 is not implemented, any game that uses the Color Select Register to change the palette will show the cyan, magenta and white palette, even though that is not what was intended.  Also, the cyan, red and white palette will not appear, the default palette will be used.

Bit 4 determines whether the palette colors are in low or high intensity.  It works for all three palettes described above.  Thus green, red and brown becomes light green, light red, yellow; cyan, magenta and white become light cyan, light magenta and high intensity white; and cyan, red and white becomes light cyan, light red and high intensity white.  Since bit 4 is not implemented on the PCjr. games will only use the low intensity palettes.

Thus on CGA there are really six palettes available :

IBM PC CGA Mode 4 Palette 1 Low Intensity :

Ultima II - Revenge of the Enchantress

IBM PC CGA Mode 4 Palette 0 Low Intensity :

Digger

IBM PC CGA Mode 5 Palette 0/1 Low Intensity :

Donkey Kong

IBM PC CGA Mode 4 Palette 1 High Intensity :

Battlezone

IBM PC CGA Mode 4 Palette 0 High Intensity :

Shamus

IBM PC CGA Mode 5 Palette 0/1 High Intensity :

Tapper

On the PCjr., however, there are really only two palettes available for games that aren't PCjr. aware, if they work at all :

IBM PCjr. "CGA" Mode 4/5 Palette 1 :

Ultima II - Revenge of the Enchantress

IBM PCjr. "CGA" Mode 4/5 Palette 0 :

Shamus

Note that for PCjr. CGA Palette 1, cyan and magenta are the same as real CGA, but white has become high intensity white.  This is intentional and has been verified on real hardware.  Apparently IBM decided the original palette was not bright enough and so decided to brighten things up a bit.  For PCjr. CGA Palette 0, the intense palette is not available, even for games that intended to use it.  However, several games that used Palette 0 will use Palette 1 on the PCjr. because they used a register write instead of the BIOS function to set the palette.

However, in a 4-color mode, the PCjr. is not limited to the 78 possible combinations of the three preset colors and the background color.  Through its palette registers, the PCjr. can set each of the four colors to any color in the 16-color palette.  1,820 combinations become available.  Likewise, in a two color mode, the PCjr. can set the foreground and background colors independently, and the background color need not be black.  In addition, the PCjr. can set the border color independently in any mode, whereas the CGA can only set a unique border color in text modes.  Instead of only fifteen choices, 120 choices become available.

Even though Tandy copied the PCjr.'s video gate array and graphics capabilities, it restored the Mode Control and Color Select Registers giving it near perfect compatibility with any non-Tandy aware CGA program using the those registers.

Youtube Sucks for Retrogaming Videos

When it comes to videos showing footage of real retro PC and console games, Youtube and the other major video sharing sites suck.  Here is why :

1.  Standard Definition Frame Rate and Aspect Ratio

Normal TVs output a standard resolution : a 525/480 (output/visible) line resolution interlaced at 29.97Hz for NTSC and a 625/576 line resolution at 25Hz for PAL.  The video is interlaced, with odd lines of a frame being displayed first, then the even lines.  Although the TV may be drawing lines 50-60 times per second, the actual number of frames in video is 25-30 per second.  The horizontal resolution with analog broadcast or recording equipment (tape) could be anywhere from 300-600 color dots per line.  Eventually, by the time of DVD, NTSC and PAL video would be able to display 720/704 horizontal dots, and the 4:3 aspect ratio would constrain the visible pixels to fit within the frame.

When Youtube and other video sharing sites were first being implemented, this was the maximum resolution they supported.  In the beginning, with many amateur filmmakers using whatever kind of video equipment they could find, this was not really a big deal.  Youtube also supported 320x240 and 480x360 resolution modes in addition to a 640x480 resolution mode.

Eventually Youtube added support for 720 and 1080 line modes and 16:9 widescreen modes.  In fact, all videos are shown in the 16:9 video window, and 4:3 content is pillarboxed.  All videos can use be seen in any of the following formats :

192x144*
256x144
320x240*
428x240
480x360*
640x360
640x480*
854x480
960x720*
1280x720
1440x1080*
1920x1080

* - Pillarboxed resolutions

While Youtube describes its resolutions as 720p and 1080p, the maximum frame rate is 30 non-interlaced frames per second.

2.  Home Computer and Console Frame Rate

Every computer and classic console prior to the Sega Genesis and Super Nintendo almost exclusively output a video signal at either 60 frame per second for NTSC systems or 50 frames per second for PAL systems.  Thus the Atari 2600 usually supported a 160x192 resolution, the Apple II, 280x192, the Atari 8-bit,  320x192, the Commodore 64, 320x200, the IBM PC with CGA 640x200, the Colecovision and Sega Master System, 256x192 and the NES, 256x240.   The Sega Genesis and Super Nintendo did support high resolution interlaced graphics, but games stuck with the low resolution modes 99.9% of the time.  Some home computers like the Amiga and add-on cards like the IBM 8514/A did support an interlaced signal, but this was rarely used due to the flicker perceived by the short distance between the user's screen and eyes.  These early consoles and computers traded graphic resolution for frame rate, primarily to reduce distracting flicker.  Handheld consoles like the Gameboy, Sega Game Gear, Nomad, Gameboy Advance all support 60 frames per second.

The IBM PC and compatibles did not vary refresh rate by country but instead by display adapter.  The monochrome and Hercules cards used 50Hz, the CGA, PCjr., Tandy 1000 and EGA adapters 60Hz and the VGA, SVGA and later adapters 60Hz, 70Hz, 72Hz, 75Hz, 85Hz.  When LCDs overtook CRTs in computer display technology, 60Hz to 75Hz was generally deemed sufficient for fluid gameplay, as flicker was no longer an issue.  3D screens in 3D mode use 120Hz because twice as many images are being displayed.

For gaming consoles, only with the Playstation, Nintendo 64 and Sega Saturn did interlaced modes show some significant use, but they did not truly become popular until the Playstation 2.  Most Dreamcast and Gamecube and Xbox games could be played in 480p progressive scan (60 frames per second) through the use of special VGA or component video cables.  A much smaller proportion of games for the Playstation 2 support progressive scan.  The Nintendo Wii supports 480p over component video cables and the Playstation 3 and Xbox 360 generally use 720p for HD games.

3.  The Problems

If you post game footage to Youtube, either taken by a video capture device or an emulator, Youtube is going to convert your video.  Since it will not display native 60 frames per second video, it will convert it to 30 frames per second.  This can be done by dropping every other frame, or by interpolating two or more adjacent frames to make one frame.  However, as either method would cut the running time in half, each frame may be repeated.  This plays havoc with the motion within the game footage.  It looks jumpy as though it was being played on a poor emulator.

The other issue is the scaling algorithms used.  Say I take some emulator footage of a NES game.  The emulator has no filters, no scalers, just pure 256x240 graphics at 60 frames per second.  The pixels are crisp, sharp, clear.  Each pixel is the same size and each color is clearly distinct.  This is the purest form of capture you can get, provided of course you use an accurate emulator like Nintendulator or Nestopia.  The resulting video may be losslessly compressed, but Youtube does not display losslessly compressed video, no matter how small it may be.  DOSBox 0.74 and Yhkwong's SVN has a lossless video codec which it uses to record, and since DOSBox is highly accurate, it is by far easier to capture video from DOS games using it, especially pre-VGA, than from real hardware.

I posted a test video here : http://www.youtube.com/watch?v=zOffjiGXhBQ  This video was originally recorded using Nestopia - Undead Edition 1.45, a very accurate emulator.  I decided to use the 2C03 RGB PPU palette (without the extra grays Nestopia inserts) to simulate as accurately as possible the ideal capture from the real machine using the highest quality output that would be readily available.  The 2C02 PPU, found in every consumer-based NES or Famicom except the Famicom Titler, can only output composite video.

While most of my run through the stage is not too bad, things really start to look wrong when Mega Man fights the boss.  There is a fair amount of flicker on real hardware or the emulator as this part of the game really goes beyond the 64 sprite limit of the NES.  However, the result is nowhere near as bad as the the video makes it out to be, and just ends up distracting.

In addition, my video was pixel perfect, no interpolation shown when viewing it at its native resolution.  Youtube does not offer an "exact size" setting for the video window.  To be fair, 256x240 is really too small to watch unless you have a low resolution monitor.  However, there is no x2 or x3 scaling available.  The smallest window size is 384x360, the larger window size is 512x480 (an ideal 2x) and the full-screen mode is whatever the native resolution of your monitor is with pillarboxing.  All scaling uses typical bilinear or bicubic sampling, so what were sharp pixels appear fuzzy.  Nearest neighbor interpolation is easier computationally, but not available.

If you download an MP4 of the video, and there are many utilities you can use to do this, you can see the video in its native size without interpolation.  It will appear sharp.  However, Youtube's conversion process has done its damage to the frame rate, which as you will now see is 30 fps.  Here you can compare for yourself :

[links removed]

Unfortunately, if you wanted to see my playthrough video at it was meant to be seen, you cannot view it in a browser, you must go to the trouble of downloading it.  And this is with a perfect video capture.  Captures from real hardware frequently look like crap between the capturing device (most not designed for vintage consoles and computers and not designed for pixel-perfect accuracy, if that can be done for analog video) and Youtube's conversion.  I used to host videos of my classic computers on Youtube, but since I only had a cell phone camera (which will take video only at 30fps), the video always looked bad and flickery, something Youtube can do nothing to improve.  To be fair, it was not Youtube's fault, so I took them down.

Nestopia and DOSBox use the ZMBV capture codec to capture video with lossless compression and the accompanying audio.  It is an excellent way to capture 8-bit video, and for NES video, the resulting file size is an average of 7MB per minute.  If you did a two-hour playthrough of a game, the resulting file size would only be 840MB at the native resolution and frame rate.  This is a very reasonable file size, and while Youtube does recognize ZMBV encoded AVI files, it will compress them and the first casualty will be the frame rate.

Windows 98 Tips #1

Accessing DOS

Microsoft Windows 95 and 98 use Real Mode DOS as a boot loader.  Windows provides all the services a well-behaved DOS program needs to function.  It also allows DOS programs to directly access hardware.  However, certain functionality found in the GUI Windows environment is lost if you must use Real Mode MS-DOS unless you know how to restore it.  For games this is chiefly mouse and CD-ROM support.  You may or may not need sound card drivers, depending on the sound card you intend to use for DOS.

Many DOS games will not play at all, or optimally, when run under any Windows 9x system.  See here for Microsoft's list : http://www.vogons.org/viewtopic.php?f=5&t=761&p=28650&hilit=Microsoft+knowledge#p28650
You will need to run them in MS-DOS Mode.  In Windows 98SE, there are four ways by which Microsoft will allow you to use the DOS command line interface.

Command Propmpt Application - This provides the DOS command line interface in a window.  It may look like DOS, especially if you set it to full screen, but it is really Windows allowing you to input commands using the DOS command line prompt.  It is useful if you are trying to run an executable with variables, but it will not otherwise make your DOS game more compatible with Windows.  It does not support Very Long Filenames (none of these methods do), and it will truncate them to the first six characters followed by a ~1, then the extension.   It can also be opened by the file DOSPRMT.PIF in the WINDOWS directory.

Restart in MS-DOS Mode - This will give you a basic, real-mode DOS environment.  By default, it acts like the only thing loaded is your CONFIG.SYS file is HIMEM.SYS and DOS=HIGH.  If you have a Sound Blaster card installed, it will set the SET BLASTER environment variable in DOS.  It is found on the start menu as a shut down option, but can also be activated with the Exit to Dos.PIF in the Windows directory.  About the only thing you may be able to load without games complaining about too little Conventional Memory is the Cutemouse driver.  However, it will allow games that refuse to run with EMM386.EXE to work.  Windows 98 does not provide a mouse driver for real-mode DOS.  

MS-DOS Mode for Games - This .PIF, found in the Windows file, will give you all the benefits of Restart in MS-DOS Mode plus it will load EMM386.EXE with the NOEMS option, giving you access to the Upper Memory Area (UMA).  The CONFIG.SYS file will load DOS=HIGH,UMB instead.  Unfortunately, unlike Restart in MS-DOS Mode, it will cause your system to reboot.  This will allow you load device drivers and TSR programs in Upper Memory to conserve precious Conventional Memory for DOS games.  XMS Memory will be available, but more games used EMS Memory.  

MS-DOS Mode for Games with XMS and EMS Support -  This .PIF, found in the Windows file, will give you all the benefits of MS-DOS Mode for Games and it will by default allow for 4MB of EMS Memory.  EMS was the most popular method to access memory above 640KB and programs used it until 32-bit DOS Extenders became popular in 1994.  Many games supporting Sound Blaster digitized sound and most CD-ROM titles from the 1991-1993 either required it or supported it.  The actual provision of EMS will require 64KB that could otherwise be used as an Upper Memory Block, and this becomes extremely important when loading the Windows 98 default MS-DOS CD-ROM driver, OAKCDROM.SYS.

You can edit Exit to DOS, MS-DOS Mode for Games and MS-DOS Mode for Games with XMS and EMS Support.  You need to right click on the icon, click on properties on the drop-down menu, click on the Program tab and click on the Advanced button.  The next Window will give you boxes to change the lines of CONFIG.SYS and AUTOEXEC.BAT.  Remove the word REM from the lines you wish and add new parameters.  Note that in Windows 98SE, the path where OAKCDROM.SYS is indicated is incorrect.  

CD-ROM and Upper Memory - If you have an IDE/ATAPI CD-ROM or DVD-ROM drive, Windows 98 has a device driver called OAKCDROM.SYS which will mount the drive as a CD-ROM drive in Real Mode DOS.  When Windows 98SE is installed, you can find the file on the startup disk or if you make a recovery disk.  It is a bloated driver and requires 35K of precious memory, so I highly advise using VIDE-CCD.SYS instead, which only requires 5K of memory.  The CD-ROM driver is loaded in CONFIG.SYS in one of the following ways :

DEVICE=C:\WINDOWS\COMMAND\EBD\OAKCDROM.SYS [VIDE-CCD.SYS] /D:MSCD001 (if no UMBs are available)

DEVICEHIGH=C:\WINDOWS\COMMAND\EBD\OAKCDROM.SYS [VIDE-CCD.SYS] /D:MSCD001 (if UMBs are available)

However, loading the device driver is not enough.  For DOS to access it as a disk drive, the MSCDEX.EXE TSR must be loaded.  It is loaded in your AUTOEXEC.BAT file like this :

C:\WINDOWS\COMMAND\MSCDEX.EXE /D:MSCD001

If you have access to UMBs, you can place LH before the path to load MSCDEX in a UMB.  

OAKCDROM.SYS (35K) and MSCDEX.EXE (27K) are by far the largest programs you will ordinarily load into the Upper Memory Area.  By default, Windows will provide approximately 96K of Upper Memory in the MS-DOS Mode for Games mode, but only 32K of Upper Memory in the MS-DOS Mode for Games with XMS and EMS Support mode.  (This is another reason for you to replace OAKCDROM.SYS.)  If you have a CD-ROM game and it needs EMS Memory, try running it in Windows first.

File Transfers using Network Neighborhood

So having Windows installed on your vintage machine, how can you transfer files from a more modern system?  There are many methods.  Some of the most basic, but most annoying are floppies and CD-RWs.  USB sticks or drives may or may not work.  It tends to depend on whether a generic mass storage driver will work with Windows 98 and the drive.  Compact Flash cards are natively supported as IDE devices, but as removable devices you may not get them to work.

The best method, in my experience, is to use network transfers.  Windows 98 has support for file and printer sharing and can talk to Windows NT Networks.  PCI Network cards are cheap and easy to find for Windows 98, and Windows 98SE may have drivers for them out of the box.  The 3Com cards are especially popular and supported out of the box (except for the Gigabit cards).

Once you have your network card's drivers installed, install file and print sharing from the network properties in the control panel.  Then right click on a folder in Windows Explorer and share it.  Make sure that the network name on your Windows 98 machine matches the network name on modern system.  The default name is usually WORKGROUP.  On your modern computer, you should now see your Windows 98 computer on the network.

If your modern PC is running Windows 2000 or XP, you can typically access it with the Windows 98 machine.  With Windows Vista or 7, you cannot access your modern machine through Windows 98 by default.  There may be a method to allow access, but it is not necessary because when you share a folder on the Windows 98 machine, any other machine can copy files to that folder if you set the folder on the Windows 98 machine to allow full access.  With Network Neighborhood, you have a convenient method to send files to your computer without needing physical media.  

320x200 : The Resolution of Choice for the IBM PC

IBM decided that its Color/Graphics Adapter would support a 320x200 pixel resolution in its "medium" resolution graphics modes.  In its 40-column text mode, the 8x8 character cell would given an equivalent resolution with 25 rows on the screen. The 16KB CGA card could only display 4 colors on the screen at one time from a 16 color palette, barring graphics tricks.  It also supported a high resolution graphics at 640x200 pixels with one color freely selectable, but this was comparatively seldom used except when games turned it into a 160x200 pixel mode using color composite graphics.  Its 80-column text mode would, with 25 rows and an 8x8 text box, correspond to the 640x200 pixel resolution.

IBM did not offer a color display at the launch of the PC.  It was assumed that most users would connect the CGA card directly to a color composite monitor or to a TV via an RF modulator.  While NTSC-standard color displays could support up to 240 visible lines without interlacing, a large portion of the visible area of the screen on these devices could be obscured by the physical shell surrounding the glass monitor.  Previous home computers from Apple and Atari only supported 192 pixels as a result.  IBM's 200 pixels was hardly likely to tax the newer displays of the 1980s, which showed a more rectangular viewing area than the more circular TV screens of earlier decades.  In 1983 IBM released its 5153 PC Color Display, which provided official RGBI support from the Corporation.  This monitor had a vertical size control, which could accomodate 240 lines quite easily.  The CGA card hardware and 16KB of RAM, could not.

Jill of the Jungle CGA 320x200x4 Mode

The next widely-used graphics advances were the PCjr.'s Enhanced CGA graphics, later cloned by Tandy and known then as Tandy graphics.  This also primarily used a 320x200 pixel graphics mode with 16 colors available, but also supported a true but seldom used 160x200x16 low resolution graphics mode and a very rarely used 640x200x4 graphics mode.  IBM's PCjr. was only CGA compatible at the BIOS level, but Tandy's Graphics Adapter was CGA compatible at the register level.  The PCjr. and Tandy graphics adapters took from 16-32KB of system RAM for its graphics RAM depending on the mode.

IBM's EGA card also supported a 320x200x16 graphics mode, and this was by far the most frequently used graphics mode in EGA-supporting games.  The EGA could also support a 640x200x16 graphics mode and was backwards compatible with CGA at the BIOS level.   Tandy Graphics and EGA graphics would almost invariably look the same, but the hardware was very different.  Tandy's Enhanced Graphics Adapter, introduced with the Tandy 1000TL and 1000SL also supported a 640x200x16 mode, but few programs used it as it was not EGA compatible.  Amstrad's CGA adapter also supported a unique 640x200x16 mode, but few programs used it.

Jill of the Jungle EGA 320x220x16 Mode

All the above graphics modes worked on the same type of monitor, a digital TTL RGB monitor only capable of selecting sixteen colors.  This monitor supported the same NTSC horizontal (15.75KHz) and vertical (60Hz) scan rates of the television set.  For the EGA, IBM also included support for a 640x350 line mode with 16 colors selectable out of a 64 color palette.  This mode only worked on a special color monitor, the 5154 PC Enhanced Color Display, which supporting a higher horizontal scan rate (21.8KHz) and the ability to select 64 colors through digital TTL RGB inputs.  The standard IBM EGA card only came with 64KB, but the 640x350x16 mode required a 128, 192 or 256KB of RAM on the card.  Most clone cards came with 256KB standard.

In 1987, IBM introduced the VGA and new corresponding monitors.  VGA supported a 320x200x256 graphics mode with a palette of 262,144 colors available.  This was the mode most frequently used by games. VGA was backwards compatible with EGA at the register level and CGA at the BIOS level.   It also supported a 640x480x16 mode, but far fewer DOS games used it.  Windows 3.0 and above would use it for its default graphics display.  A new monitor was required to display the much larger color palette of the VGA compared to the CGA and EGA.  Analog color monitor outputs were used.  The high resolution display supported a 31.5KHz scan rate and 70Hz vertical refresh rates for all VGA modes, including emulated modes, except for the 640x480 mode, which used 60Hz.  200-line modes would be double scanned, with each pixel being double-clocked and each vertical line being repeated to fill up the refresh rate.  This gives a different kind of scan-line structure compared with earlier monitor.

Jill of the Jungle VGA 320x200x256 Mode

By the time of VGA, the 320x200 resolution had found support in many non-IBM PC compatible home computers.  The Commodore 64 used a 320x200 resolution and a derived 160x200 resolution.  The Atari ST, Commodore Amiga and Apple IIgs all used a 320x200 (and to a far lesser extent 640x200) resolution with varying degrees of color and palette support.  While the PAL Amiga supported 256 lines by default, most games used 200 lines for extra speed.  Those squished screenshots of Amiga games (compared to other systems) display that way on PAL machines.

Most VGA games only supported 320x200x256 graphics mode.  The BIOS mode, Mode 13h, was easy to program for but somewhat limited.  Eventually programmers found out how to create custom resolutions by using the VGA hardware registers, the so-called Mode X.  Mode X typically comprised of 320x240 pixels, which gave square pixels.  Epic Pinball and The Last Vikings used this mode.  Some games used a 320x400 graphics mode, which was easy to obtain on VGA hardware.  Programmers had to be careful to ensure that their custom mode would be compatible with the wide variety of VGA adapters in the marketplace.  Standard 256KB VGA can support any combination of 320 or 360 horizontal pixels by 200, 240 or 350 vertical pixels with 256 colors.

I have included screenshots of Jill of the Jungle above.  Jill supports all 320x200 in all three color modes.  The game does not support 320x200x16 graphics on an IBM PCjr. or Tandy 1000 Graphics adapter (few if any shareware games supported the unique graphics modes these adapters), it will use the 320x200x4 mode instead.  Except for Jill's face, the graphics are virtually identical, pixel-wise, across the three modes.  Many games down-convert the graphics using an algorithm to eliminate the need to have two extra sets of graphics images or tiles on the disk.

320x200 has a 1.6 pixel aspect ratio.  To get truly square pixels, a 4:3 display must have letterboxing.  A 16:10 1280x800, 1920x1200 or 2560x1600 widescreen monitor can display the resolution perfectly using nearest-neighbor interpolation.  However, when the resolution was used all displays were 4:3, and most users would stretch the 200 vertical lines to fill up the screen.  Instead of perfectly square pixels, you would get pixels 1.2 times as vertical compared with the horizontal width on a monitor where the vertical width had been stretched to the edges of the monitor.  Most graphic artists assumed this and adjusted their graphics accordingly, but not all did.

An illustrative example.  Look at this screenshot of Elite Plus, using the VGA 320x200x256 graphics mode.

You can see that the circle is a circle in the 1.6:1 aspect ratio.  But when converted to a 4:3 aspect ratio :

The circle has become an oval.  Thus it would seem that the 1.6:1 aspect ratio is correct for this game.

Let's look at another game, LOOM.  Here is a screenshot with a clearly spherical object in it :

Looks a bit squat in the 1.6:1 aspect ratio.  If we stretch the aspect ratio :

Now the crystal ball looks like a sphere in a 4:3 aspect ratio.  Click the 4:3 images for an undistorted, pixel-perfect resize but huge (1600x1200) version of the screenshot.

Even when Windows 95 was released, most graphically intensive games for the PC were still being released for DOS.  Only in 1997, with the acceptance of 3D accelerators, DirectX and the undeniable dominance of the Windows platform did high-performance games finally require Windows.  Most games up to this point either only supported 320x200 (DOOM, Daggerfall) or offered it as the default resolution (Duke Nukem 3D, Quake).  SVGA was not well-supported because each chipset had its own way of offering higher resolution modes, and by the time VESA modes were widely supported, Windows 95 was the gaming OS of choice.  At this point, 640x400x256 and 640x480x256 graphics were the norm.