Re: PROBLEM: Bad Graphics Mode Video on Apple II+

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

Bryan Villados wrote:

>I'm having video problems with my Apple II+. I'm currently using a composite
>color monitor to view on. Video in text mode looks great. However, when the
>video switches to hi-res (could also have a problem with lo-res, but I
>haven't tried it yet), it's looks really bad. I took a snap-shot of the
>display running Lode Runner:
>
>http://www.macgeek.org/temp/DSC00068.JPG
>
>Thanks for any advice! :)

Unfortunately, the nature of composite color pretty well precludes getting
crisp monochrome text, since any "crisp" feature will be interpreted as
chrominance information and result in significant color fringing.  In fact,
this is the name of the game for Apple II's to produce color!  That's why
the same vertical line of pixels changes to its color complement when
you move it left or right one display pixel--the Apple II dot frequency is
twice the color subcarrier frequency, so a one pixel shift is 180 degrees
around the hue circle.

The standard filtering in a composite color monitor to separate chrominance
information from luminance (intensity) information will limit the bandwidth
of the luminance signal to less than 3MHz, resulting in fuzzy text, even
when there is no color burst in the signal.

The Apple Composite Display uses some special tricks to disable the
luminance filtering when no burst is present, so monochrome text looks
crisp (even at 80 columns), but when the burst is on, as it is for any
graphics display mode, the filter is on and the bandwidth is limited.

Assuming that you're using a Apple Composite Display, it has a manual
switch on the front panel to disable color filtering and display, so if you
push it you'll have a crisp, monochrome graphics/text display.

You have to choose between crisp monochrome and fuzzy color--that's
just the way composite video is.  ;-(

-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/