VOGONS


CGA intensity

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First post, by PlaneVuki

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Hi.

In cga pinout there are 4 color pins, R G B I.

Does the intensity bit make existing color brighter or mixes it with white?

For example: rgbi=1001
Is this seen as a brighter red or a mix of red+white on screen?

Thanks n advance.

Reply 1 of 5, by reenigne

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Mix of red and white. Switching on the intensity bit increases the output to the red, green and blue electron guns. For red, the non-intense version is usually #aa0000 and the intense version #ff5555.

Reply 3 of 5, by reenigne

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Not on a standard CGA RGBI monitor, no. There are some sRGB colours that are just outside the CGA RGBI gamut, even with dithering. This wasn't fixed until we had EGA monitors (with the 350-line mode) and VGA monitors.

Reply 4 of 5, by Benedikt

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Technically, an RGBI monitor is free to interpret the meaning of “high intensity red” whichever way it wants.
You could therefore try to find an RGBI monitor that only boosts the brightness of active primary colors.
Aside from that, modding appears to be your only option.

Reply 5 of 5, by mkarcher

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Benedikt wrote on 2022-05-16, 17:19:

You could therefore try to find an RGBI monitor that only boosts the brightness of active primary colors.

That hypothetical monitor needs to make an exception for color 8 (intensity only), because otherwise it would be indistinguishable from color 0. Special casing colors is standard in CGA monitors, though, as dark yellow is remapped to brown.