English Amiga Board


Go Back   English Amiga Board > Main > Retrogaming General Discussion

 
 
Thread Tools
Old 24 February 2009, 08:48   #1
keropi
.
 
Join Date: Oct 2004
Location: Ioannina/Greece
Posts: 5,038
Question 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 09:26.
keropi is offline  
AdSense AdSense  
Old 24 February 2009, 09:32   #2
alexh
Thalion Webshrine
alexh's Avatar
 
Join Date: Jan 2004
Location: Oxford
Posts: 11,942
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
alexh is offline  
Old 24 February 2009, 09:40   #3
keropi
.
 
Join Date: Oct 2004
Location: Ioannina/Greece
Posts: 5,038
thanks alexh!!! I did forget about wikipedia!
keropi is offline  
Old 24 February 2009, 14:02   #4
cosmicfrog
The 1 who ribbits
cosmicfrog's Avatar
 
Join Date: Apr 2006
Location: leek, Staffs, UK
Age: 50
Posts: 3,555
Send a message via MSN to cosmicfrog
thanks for that keropi & alexh, learn something new every day
I have clear memory of cga but never knew about the composit thing
cosmicfrog is offline  
Old 24 February 2009, 14:15   #5
drHirudo
Amiga user
drHirudo's Avatar
 
Join Date: Nov 2008
Location: Sofia / Bulgaria
Posts: 140
Quote:
Originally Posted by cosmicfrog View Post
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.
drHirudo is offline  
Old 24 February 2009, 15:12   #6
cosmicfrog
The 1 who ribbits
cosmicfrog's Avatar
 
Join Date: Apr 2006
Location: leek, Staffs, UK
Age: 50
Posts: 3,555
Send a message via MSN to cosmicfrog
yhear mori patterns are nothing new in the world of tv monitors
cosmicfrog is offline  
Old 24 February 2009, 15:39   #7
amiga
Registered User
 
Join Date: Aug 2004
Location: Amiga_land
Posts: 444
Quote:
Originally Posted by keropi View Post
'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.
amiga is offline  
Old 24 February 2009, 21:23   #8
alexh
Thalion Webshrine
alexh's Avatar
 
Join Date: Jan 2004
Location: Oxford
Posts: 11,942
Quote:
Originally Posted by cosmicfrog View Post
yhear mori patterns are nothing new in the world of tv monitors
Moire even
alexh is offline  
Old 24 February 2009, 21:42   #9
meega
Secret Lemonade Drinker
meega's Avatar
 
Join Date: Dec 2007
Location: Oooh what a feeling yeaaah dancing on the ceiling
Posts: 313
Moiré.
meega is offline  
Old 24 February 2009, 22:05   #10
alexh
Thalion Webshrine
alexh's Avatar
 
Join Date: Jan 2004
Location: Oxford
Posts: 11,942
I can never remember how to get that character..

ALT + (numeric keypad) 130 ?

é

Yup
alexh is offline  
Old 24 February 2009, 22:41   #11
discomeats
Just add brown sauce.
discomeats's Avatar
 
Join Date: May 2008
Location: North East Englandland
Posts: 170
I knew someone would just *have* to correct that
discomeats is offline  
Old 24 February 2009, 22:44   #12
alexh
Thalion Webshrine
alexh's Avatar
 
Join Date: Jan 2004
Location: Oxford
Posts: 11,942
Either way it dont matter cos these colour smears are not moiré patterns
alexh is offline  
Old 24 February 2009, 23:49   #13
discomeats
Just add brown sauce.
discomeats's Avatar
 
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
discomeats is offline  
Old 25 February 2009, 15:25   #14
cosmicfrog
The 1 who ribbits
cosmicfrog's Avatar
 
Join Date: Apr 2006
Location: leek, Staffs, UK
Age: 50
Posts: 3,555
Send a message via MSN to cosmicfrog
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 ...
cosmicfrog is offline  
Old 27 February 2009, 11:20   #15
pce_gamer
Registered User
 
Join Date: Feb 2009
Location: arizona
Posts: 29
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
pce_gamer is offline  
Old 27 February 2009, 11:25   #16
killergorilla
Lesser Talent
killergorilla's Avatar
 
Join Date: Jan 2003
Location: UK
Age: 36
Posts: 7,924
Quote:
Originally Posted by alexh View Post
I can never remember how to get that character..

ALT + (numeric keypad) 130 ?

é

Yup
Or "Alt-Gr + e"
killergorilla is offline  
Old 27 February 2009, 13:36   #17
cane
Registered User
cane's Avatar
 
Join Date: Aug 2005
Location: .hr
Age: 38
Posts: 539
Quote:
Originally Posted by killergorilla View Post
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.
cane is offline  
Old 27 February 2009, 13:43   #18
keropi
.
 
Join Date: Oct 2004
Location: Ioannina/Greece
Posts: 5,038
we had ALT-GR marking here in Greece too..
keropi is offline  
Old 27 February 2009, 14:21   #19
cosmicfrog
The 1 who ribbits
cosmicfrog's Avatar
 
Join Date: Apr 2006
Location: leek, Staffs, UK
Age: 50
Posts: 3,555
Send a message via MSN to cosmicfrog
well on my keyboard

Alt-Gr + 4 = €
Alt-Gr + e = é
@ is shift ' between ; and #
cosmicfrog is offline  
Old 27 February 2009, 16:53   #20
discomeats
Just add brown sauce.
discomeats's Avatar
 
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
discomeats is offline  
AdSense AdSense  
 


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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Amiga RGB to S-Video + composite adaptor narmi Hardware pics 431 11 September 2017 20:23
RGB to S-Video / Composite Adaptor Charlie Hardware mods 3 30 January 2011 15:13
A600/A1200 RGB to Composite Converter crazyegg support.Hardware 11 25 September 2009 00:19
Will Classic Workbench Adv display through composite outputs? Fingerlickin_B project.ClassicWB 12 09 June 2007 12:38
RGB 2 Composite Rod_cl support.Hardware 6 08 November 2006 22:20

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 20:29.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Page generated in 0.37860 seconds with 11 queries