Path: utzoo!utgpu!water!watmath!clyde!rutgers!mit-eddie!uw-beaver!fluke!mason
From: mason@tc.fluke.COM (Nick Mason)
Newsgroups: comp.sys.ibm.pc
Subject: Re: EGA color palatte
Message-ID: <2642@fluke.COM>
Date: 12 Jan 88 16:04:33 GMT
References: <2310@nicmad.UUCP>
Sender: news@tc.fluke.COM
Distribution: na
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 82


Hi. I also have been working with the IBM-EGA card.

In article <2310@nicmad.UUCP> you write:
>
>	MSB  LSB
>	 rgbRGB   where r=32, g=16, b=8, R=4, G=2 and B=1
>		  and rgb are secondary pins and RGB are primary pins

The above is correct.
>
>Along the same line, does the RGB connector (IBM connector mode 1) always
>have 4 pins, ie, RGB and I [intensity].  The other connection of the RGB
>connector (IBM connector mode 2) has 6 pins used, hence the 64 possible
>colors.  And we also have RGB Analog, which I call RGBA.  What I would
>like to know is what exactly are all the various types of RGB pinouts
>and what their names are.  We have RGB, RGBI and RGBA bantered around,
>so what exactly is what?  Is the 4 pin RGB called RGBI and is the 6 pin
>RGB just called RGB?
>

The common use of RGB, RGBI, and RGBA as I have seen them used are:

RGB: a mode with 3 bits for 8 colors.

RGBI: the above plus "intensity" , a 4 bit mode for 16 colors.

RGBA: an analog mode with lots of colors.

RGB and RBGI are digital modes, typically tied to a specific type of
monitor that is only capable of producing specific discrete colors.
RGBA requires an analog monitor that can take a varying input voltage.
Ever notice the price differences between an analog and digital color
monitor?

I have never read about connector mode 1 and 2.  It looks interesting,
what is your reference?


My model of the EGA is as follows.  You can display 16 colors out of
the possible 64 colors at any time.  The 64 colors use the rgbRGB scheme
you have described above.  However, the EGA card has 4 memory planes,
corresponding to 4 bits per pixel.  .ie. each pixel on the display has
a value between 0 and F hex.  This is mapped into the Look UP Table (LUT)
that has 64 possible modes.  This LUT feeds the circuits that drive the
monitor and display colors on the screen.

For example, :

pixel value   Default LUT   a blue/gray scale LUT
	0	0		0
	1	1		8
	2	2		1
	3	3		18
	4	4		11
	5	5		3
	6	6		29
	7	7		F
	8	38		1D
	9	39		2B
	A	3A		39
	B	3B		19
	C	3C		9
	D	3D		1B
	E	3E		6
	F	3F		7

The pixel value is the value in the bit planes, the LUT are the 16 mapped
values out of the 64 possible.

To work through a few values,
pixel=0, default LUT=0H=rgbRGB=000000=black.
pixel=1, default LUT=1H=rgbRGB=000001=blue.
pixel=2, default LUT=2H=rgbRGB=000020=green.
etc.
>Here is the color table as I know it.  Could someone please fill in the
>blanks, or correct same?
I have looked at all of the colors but I have simply classified them
into green, blue, red, orange, etc. since I am no color expert and
don't have enough names for the x shades of green I found.

Hope this helps.