Color Palette
The EGA palette allows all 16 CGA colors to be used simultaneously, and it allows substitution of each of these colors with any one from a total of 64 colors (two bits each for red, green and blue). This also allows the CGA's alternate brown color to be used without any additional display hardware. The later VGA standard built on this by allowing each of the 64 colors to be further customized.
When selecting a color from the EGA palette, two bits are used for the red, green and blue channels. This allows each channel a value of 0, 1, 2 or 3. To select the color magenta, the red and blue values would be medium intensity (2, or 10 in binary) and the green value would be off (0). When calculating the intended value in the 64-color EGA palette, the binary number of the intended entry is of the form "rgbRGB" where a lowercase letter is the least significant bit of the channel intensity and an uppercase letter is the most significant bit. For magenta, the most significant bit in the red and blue values is a 1, so the uppercase R and B placeholders would become 1. All other digits are zeros, giving the binary number 000101 for the color magenta. This is 5 in decimal, so setting a palette entry to 5 would result in it being set to magenta. All the color values for the default colors are listed in the table on the right.
| Default EGA 16-color palette (set up to match the standard CGA colors) |
||
|---|---|---|
| Color | rgbRGB | Decimal |
| 0 – black (#000000) | 000000 | 0 |
| 1 – blue (#0000AA) | 000001 | 1 |
| 2 – green (#00AA00) | 000010 | 2 |
| 3 – cyan (#00AAAA) | 000011 | 3 |
| 4 – red (#AA0000) | 000100 | 4 |
| 5 – magenta (#AA00AA) | 000101 | 5 |
| 6 – brown (#AA5500) | 010100 | 20 |
| 7 – white / light gray (#AAAAAA) | 000111 | 7 |
| 8 – dark gray / bright black (#555555) | 111000 | 56 |
| 9 – bright blue (#5555FF) | 111001 | 57 |
| 10 – bright green (#55FF55) | 111010 | 58 |
| 11 – bright cyan (#55FFFF) | 111011 | 59 |
| 12 – bright red (#FF5555) | 111100 | 60 |
| 13 – bright magenta (#FF55FF) | 111101 | 61 |
| 14 – bright yellow (#FFFF55) | 111110 | 62 |
| 15 – bright white (#FFFFFF) | 111111 | 63 |
Read more about this topic: Enhanced Graphics Adapter
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