Reply To: Are Oakhurst/Coarsegold worth visiting?

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“… (by Johann de Waal) Thanks for the info, Chris. But are you sure about only the PCjr having the capability to display the extended palette? We only had a bog standard IBM-compatible PC with an Intel 8088 CPU and CGA graphics adapter.

I remember reading somewhere (on this site perhaps?) that it was some kind of smart software thing that Sierra did.

Later, when we got VGA, and could now play the AGI games in EGA, the graphics was a big improvement even over the extended CGA. The EGA and CGA graphics looked very different, and not similar as you mention.


Actually, Johann you were ‘nearly’ correct.

The IBM-compatible CGA modes that Sierra used only supported four of the colours from the total palette, but also used a technique called dithering to make it look like a richer palette was being used. The CGA mode used was 320×200 with 4 colours, and each horizontal pixel was two pixels wide. Dithering meant some parts of the scene had two colours painted next to each other in these “double pixels”.

For example, when you fill a rock like this (basically a whole series of vertical two-colour stripes) the colours start mixing together and looking like they are a different colour shade. The human eye tricks your brain into thinking it is a different colour on the screen.

I too loved the Sierra AGI games because it made my four-colour CGA look way better than what most games made it look like.

One of the reasons this couldn’t work effectively with SCI was because SCI didn’t have the blocky two-pixels-equals-one screen layout and thus the dithering would only work in areas that had large filled areas. The much more detailed graphics in the SCI games meant that a lot of screens wouldn’t have been able to make use of this technique.

As a side-note there was also a way of hacking the CGA to get 16 colours at a resolution of 160×100 (I think). A couple of games such as Moonbugs used this mode. There is more info about it on mobygames.