Re: Making the ][+ better

[mjmahon@aol.com (Michael J. Mahon)]

Simon Williams wrote:

>Michael J. Mahon <mjmahon@aol.com> wrote:
>
>> Rubywand wrote:
>> 
>> >     If you'd like to try building the circuit to kill color in the Text
>> >beneath
>> >graphics displays, there's a diagram pic at ...
>> >
>> >
>> >http://apple2.org.za/gswv/a2zine/Docs/DiagramsAndSchematics/TextColorKill
>> er.jpg
>> 
>> This is a fine example of a "fast" color killer, which works not by
>> putting the monitor into monochrome mode (which would take some
>> time) but by reducing the gain of the chroma subcarrier.
>> 
>> The visual result is the same, except for "clever" color monitors
>> like the AppleColor Composite, which will not have time to increase
>> its lumnance bandwidth for sharp text, as it does when it switches
>> to monochrome mode.
>> 
>> I think that there is another place in the AppleColor Composite
>> circuit where a similar circuit could be attached to switch it to
>> true monochrome mode quickly, allowing crisp 80-column text
>> under a DHR display.
>> 
>> -michael
>> 
>> Check out parallel computing for 8-bit Apples on my
>> Home page:  http://members.aol.com/MJMahon/
>
>This might be getting off topic, but does the IIc+ have something like
>this built in? I had mine hoked up to my TV and noticed that text
>display had the expected *horrible* red and green haloes, but when I ran
>anything with a HGR screen the 4 text lines at the bottom were much
>sharper and the haloes seemed much less "saturated".

I don't think that the IIc+ has any special video circuitry.

My guess is that your set has sutomatic gain control on the chroma
subcarrier average value, and a text display, having very little average
chroma, causes it to "turn up the color", while a graphics display
often has significant color, which could keep the chroma gain at
a moderate level.

Many modern sets have an "automatic" picture setting which tries
to keep the picture "normal" by fiddling with what used to be manual
controls.

An interesting experiment would be to vary the content of the
graphic screen between bright colors and black or white, and
see if the text below changes in appearance.

-michael

Check out parallel computing for 8-bit Apples on my
Home page:  http://members.aol.com/MJMahon/