Re: Newbie Apple IIgs questions

[Mitchell Spector <mitch2gs@hotmail.com>]

"Michael J. Mahon" <mjmahon@aol.com> wrote:

>Mitchell Spector wrote:
>>     Good example: Look at the fonts displayed inside a Finder window
>> on a TV set and the text actually appears in heavy bold (by no means 
>> subtle) bands of green, blue, purple and orange. The whole screen is 
>> quite literally a rainbow colored mess. Now switch over to output from a 
>> Video Overlay Card (which produces a corrected composite signal) 
>> and the black text appears greyish black. Any traces of color shifting
>> is subtle and faint, you really need to stare closely at the screen.
>
>The video overlay card does two things:  it creates standard sync and
>blanking signals (correcting the minor timing differences) and it does
>anti-aliasing of the chroma signal, so that there is less color artifact
>on, for example, dot pairs.  If a single dot is displayed, and is not
>shaped/stretched, then it must appear colored, since it represents
>an appreciable amount of chroma energy at that position.
>
>The "graying" of the black is a sign of anti-aliasing to reduce
>chroma artifacts.  This is appropriate in a screen known to be
>monochrome, but it is not appropriate if the screen is supposed
>to be color.  Normally, the "intent" is reflected in the presence
>or absence of a color burst on the "back porch" of the horizontal
>blanking pulse, but most monitors require many scan lines to respond
>to a change in color burst status, so entire fields are either color
>or monochrome, not partial fields.

    Ahh, that finally explains a little mystery about the Video Overlay Card.
When I first picked one up a couple of years ago, I noticed text and 
graphics were noticeably blurred. I thought it was a defect of my card,
I had no idea it was doing hardware based anti-aliasing.

    I've also noticed the VOC seems a bit less color saturated and there's
faint and subtle vertical banding appearing in the image. To this day I
cannot be sure if it's my specific card or a standard "feature". 

I dug up my post from 4 years ago that mentioned most of these issues
in greater detail...

http://groups-beta.google.com/group/comp.sys.apple2/msg/85c4efe85f3f6d5a?dmode=source

>>     I've used my Commodore 64 with both the split chroma-luma (essentially
>> S-Video) and regular composite, and even the latter produces a superior
>> video signal compared with the IIgs's composite-out. The same is true with
>> my Amiga, Nintendo, Super Nintendo or any other composite device.
>
>The C=64 and most video games use a technique of creating color video
>that is more like the Apple II Lo-Res color, or Apple II DHR color,
>based on 4-bit patterns shifted out at 14.3Mhz.

    That would make sense, though what about the Amiga outputting
composite video? Some of its graphic modes are very similar to the IIgs 
and yet there is no major color shifting or bleeding. It looks respectable.

Mitchell Spector