What's the deal with pc's EGA rgb and composite outputs?

keropi · 24 February 2009, 07:48

'mornin'!

I always had this question but bored to ask

what's the deal with old EGA cards that output rgb and comosite? it seems that composite has more colors, 16 to be exact, instead of the 4 rgb ones... see here for some examples:

RGB:

Composite:

anyone knows why? perhaps an link discussing the matter?
thanks!

alexh · 24 February 2009, 08:32

This was a programming technique used at first by demo programmers and then widely adopted.

They noticed that if you placed certain colours next to each other they appeared a different colour (a colour not normally available) on composite output.

Lots of games of the day on CGA and EGA used this technique of "Cross colour artifacts" sometimes known as smearing.

http://en.wikipedia.org/wiki/Color_Graphics_Adapter

keropi · 24 February 2009, 08:40

thanks alexh!!! I did forget about wikipedia!

cosmicfrog · 24 February 2009, 13:02

thanks for that keropi & alexh, learn something new every day
I have clear memory of cga but never knew about the composit thing

drHirudo · 24 February 2009, 13:15

Quote:

Originally Posted by cosmicfrog

thanks for that keropi & alexh, learn something new every day
I have clear memory of cga but never knew about the composit thing

Similar composite technique is used on the Apple II as well, only that the Apple II had 16 real colors four years before the CGA (In 1977). On RGB Apple 2 monitor the colors look sharp, on composite TV set more colors were visible, due to the composite artifacts.

cosmicfrog · 24 February 2009, 14:12

yhear mori patterns are nothing new in the world of tv monitors

amiga · 24 February 2009, 14:39

Quote:

Originally Posted by keropi

'mornin'!

I always had this question but bored to ask

what's the deal with old EGA cards that output rgb and comosite? it seems that composite has more colors, 16 to be exact, instead of the 4 rgb ones... see here for some examples:

RGB:

Composite:

anyone knows why? perhaps an link discussing the matter?
thanks!

I prefer the C64 version.

alexh · 24 February 2009, 20:23

Quote:

Originally Posted by cosmicfrog

yhear mori patterns are nothing new in the world of tv monitors

Moire even

meega · 24 February 2009, 20:42

Moiré.

alexh · 24 February 2009, 21:05

I can never remember how to get that character..

ALT + (numeric keypad) 130 ?

é

Yup

discomeats · 24 February 2009, 21:41

I knew someone would just *have* to correct that

alexh · 24 February 2009, 21:44

Either way it dont matter cos these colour smears are not moiré patterns

discomeats · 24 February 2009, 22:49

quite so, it's being clever with ntsc colour signal to make shiny new colours appear

there's a few games do this, I have a genuine cga card with video out somewhere, hopefully the 386 isn't too fast for these games

cosmicfrog · 25 February 2009, 14:25

oh no the spelling police are out

and yes i know they arn`t Moiré patterns, its just a simmilar effect

remember experimenting on old c64 in black and white on tv see if we could get some on the colours... results just something to muck about for the evening when a teenager ...

pce_gamer · 27 February 2009, 10:20

Quote:

I always had this question but bored to ask

what's the deal with old EGA cards that output rgb and comosite? it seems that composite has more colors, 16 to be exact, instead of the 4 rgb ones... see here for some examples:

I think you mean CGA. EGA has 16colors out of 64colors onscreen. CGA has 4 colors onscreen out of 8 (some sites say 16 but I don't remember having a palette that big with my old 8bit ISA composite output card). I also don't remember composite output with EGA cards, just CGA cards.

That's pretty cool though, getting 16 colors onscreen with the CGA card in 320x200 mode via color artifacting (or using 640x200 B&W mode to get a different set of 16 colors onscreen) - pic

killergorilla · 27 February 2009, 10:25

Quote:

Originally Posted by alexh

I can never remember how to get that character..

ALT + (numeric keypad) 130 ?

é

Yup

Or "Alt-Gr + e"

cane · 27 February 2009, 12:36

Quote:

Originally Posted by killergorilla

Or "Alt-Gr + e"

Slight OT, is there Alt-Gr on English keyboard? It's standard on Croatian keyboard, e.g. @ is Alt-Gr + v and € is Alt-Gr + e.

keropi · 27 February 2009, 12:43

we had ALT-GR marking here in Greece too..

cosmicfrog · 27 February 2009, 13:21

well on my keyboard

Alt-Gr + 4 = €
Alt-Gr + e = é
@ is shift ' between ; and #

discomeats · 27 February 2009, 15:53

I knew someone would post to correct about EGA cards not having video out too

24 February 2009, 07:48	#1
keropi . Join Date: Oct 2004 Location: Ioannina/Greece Posts: 5,040	What's the deal with pc's EGA rgb and composite outputs? 'mornin'! I always had this question but bored to ask what's the deal with old EGA cards that output rgb and comosite? it seems that composite has more colors, 16 to be exact, instead of the 4 rgb ones... see here for some examples: RGB: Composite: anyone knows why? perhaps an link discussing the matter? thanks! Last edited by keropi; 24 February 2009 at 08:26.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Amiga RGB to S-Video + composite adaptor	narmi	Hardware pics	431	11 September 2017 19:23
RGB to S-Video / Composite Adaptor	Charlie	Hardware mods	3	30 January 2011 14:13
A600/A1200 RGB to Composite Converter	crazyegg	support.Hardware	11	24 September 2009 23:19
Will Classic Workbench Adv display through composite outputs?	Fingerlickin_B	project.ClassicWB	12	09 June 2007 11:38
RGB 2 Composite	Rod_cl	support.Hardware	6	08 November 2006 21:20

24 February 2009, 08:32	#2
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,331	This was a programming technique used at first by demo programmers and then widely adopted. They noticed that if you placed certain colours next to each other they appeared a different colour (a colour not normally available) on composite output. Lots of games of the day on CGA and EGA used this technique of "Cross colour artifacts" sometimes known as smearing. http://en.wikipedia.org/wiki/Color_Graphics_Adapter

24 February 2009, 08:40	#3
keropi . Join Date: Oct 2004 Location: Ioannina/Greece Posts: 5,040	thanks alexh!!! I did forget about wikipedia!

24 February 2009, 13:02	#4
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	thanks for that keropi & alexh, learn something new every day I have clear memory of cga but never knew about the composit thing

24 February 2009, 14:12	#6
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	yhear mori patterns are nothing new in the world of tv monitors

24 February 2009, 20:42	#9
meega Registered User Join Date: Dec 2007 Location: Oooh what a feeling yeaaah dancing on the ceiling Posts: 314	Moiré.

24 February 2009, 21:05	#10
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,331	I can never remember how to get that character.. ALT + (numeric keypad) 130 ? é Yup

24 February 2009, 21:41	#11
discomeats Just add brown sauce. Join Date: May 2008 Location: North East Englandland Posts: 170	I knew someone would just have to correct that

24 February 2009, 21:44	#12
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,331	Either way it dont matter cos these colour smears are not moiré patterns

24 February 2009, 22:49	#13
discomeats Just add brown sauce. Join Date: May 2008 Location: North East Englandland Posts: 170	quite so, it's being clever with ntsc colour signal to make shiny new colours appear there's a few games do this, I have a genuine cga card with video out somewhere, hopefully the 386 isn't too fast for these games

25 February 2009, 14:25	#14
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	oh no the spelling police are out and yes i know they arn`t Moiré patterns, its just a simmilar effect remember experimenting on old c64 in black and white on tv see if we could get some on the colours... results just something to muck about for the evening when a teenager ...

27 February 2009, 12:43	#18
keropi . Join Date: Oct 2004 Location: Ioannina/Greece Posts: 5,040	we had ALT-GR marking here in Greece too..

27 February 2009, 13:21	#19
cosmicfrog The 1 who ribbits Join Date: Apr 2006 Location: leek, Staffs, UK Age: 56 Posts: 3,557	well on my keyboard Alt-Gr + 4 = € Alt-Gr + e = é @ is shift ' between ; and #

27 February 2009, 15:53	#20
discomeats Just add brown sauce. Join Date: May 2008 Location: North East Englandland Posts: 170	I knew someone would post to correct about EGA cards not having video out too

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)