Re: Double hires mode color artifacts

[Jerry <SNIPawanderin@yahoSNIPo.ca>]

Dirk Thierbach wrote:

> Michael J. Mahon <mjmahon@aol.com> wrote:
>> Matthew T. Russotto wrote:
> 
>>> There's the "analogtv" and "apple2" screensavers, part of the
>>> xscreensaver package.  They take up a significant percentage of the
>>> CPU of a modern machine.  As far as I know, no one has hooked one up
>>> to an Apple //e emulator.
> 
>> I haven't seen them--ironic that the heavy lifting would be
>> done first by a screen saver!  ;-)
> 
> My (older) Debian distribution doesn't include them either, but a look at
> 
> http://www.jwz.org/xscreensaver/screenshots/
> 
> shows for example that analogtv tries to simulate (high-frequency)
> noise, and still looks "blocky" and not very convincing. There's no
> screenshot for "apple2" under hires, so I don't now how it looks, and
> if "it also reproduces the appearance of display on a color television
> set of the period." doesn't just mean that it does what all emulators do.
> Can anyone check?

I think it looks quite realistic.

I'm also working (slowly) on writing a table-generator for use by the N-bit
shift-register algorithm this thread discusses.  I'm reading up on how NTSC
TV decoders really work.  I've looked at the analogtv.c source (from the
Jamie Zawinski's xscreensaver), but I'd like to start with some code that's
easy-to-understand.  His code is rather convoluted, IMO, by all the extra
signal degradations he put in.  Since I don't fully understand NTSC
decoding, I'd prefer to learn and build my algorithm up step by step.

When it's done, it will be some fruit of the ideas of various people: 
Linards T, Michael M, Vlad I, Andy M, and probably others.

-- 
--  Jerry