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Re: Apple II Graphics
Mitchell Spector wrote:
Andy McFadden <fadden@fadden.com> wrote:
heuser.marcus@freenet.de wrote:
Double Hires sure is beautiful. Is there any places where I can find
good screenshot of Apple II Lores, Hires or Double Hires images?
Picture quality of emulation often looks too sterile, IMHO.
I wholeheartedly agree. A large part of the problem are modern displays.
With old NTSC-based displays their higher dot pitch, scanlines, lack of
sharpness, etc gave the illusion of rounded pixels and colors seamlessly
blending into each other. Not to mention a form anti-aliasing, so images
looked less jagged and higher resolution than they really were. Modern
displays show images as blocky, terribly dithered and ugly looking.
When I emulate a game console or arcade machine, I prefer to output
it to my TV set (27" Sony CRT from 1989). And if I turn off interlacing, it's
virtually impossible to tell it apart from the real hardware.
I struggled with this a bit in CiderPress, which is why there are three
color conversion modes for DHR (plus black & white). Nothing quite matches
the //e DHR output, and the IIgs RGB monitor output is just plain bizarre
I remember a 1986 issue of A+ (or was it inCider?) that did a side by
side photo comparison of Hi-Res and Double-Hi-Res graphics output from a
IIe and IIgs both connected to the *same* color composite display. The GS
did odd dithering and color pattern separation that actually differed from
the IIe! (we're not even talking about an RGB display here, just composite).
The Apple II line, with the sole exception of the IIgs, generates NTSC
video "directly", by simply outputing a 14.318MHz stream of bits that
are either 1 or 0 (with the exception of the blacker-than-black sync, of
course). (In the case of hi-res, the 7MHz bit stream can be considered
to be a 14MHz stream with each bit repeated.)
All of the characteristics of Apple II video are a consequence of the
interaction of this binary stream being interpreted as an NTSC composite
video signal by a composite monitor.
The IIgs also generates a 14MHz bit stream for the traditional Apple II
video modes, but it converts them all to RGB for its native display. To
produce NTSC video, it re-converts the synthetic RGB signal to an actual
chroma signal and luminance signal, then mixes them to create a true
composite signal.
This means that IIgs composite output is *not* an Apple II video stream,
but is a composite signal synthesized from its RGB interpretation of
an Apple II video stream.
As noted above, that RGB interpretation is relatively unsophisticated,
and does not reproduce many of the subtleties that result when the
raw bit stream is interpreted by an NTSC monitor.
Although the native RGB characteristics of the IIgs in its native SHR
modes allows for very beautiful graphics, its hardware is incapable of
producing the simple NTSC video displays that were unique to the Apple
II line of computers. This causes the IIgs to be a relatively poor
machine for displaying the graphics that were designed for earlier
Apple II machines.
(e.g. the color of a pixel is affected by the colors of the pixels to
its left and right, but it still has the hard edges of an RGB image).
Is that the odd artificating you see in standard 6 color Hi-Res on
the IIgs? I've seen Double-Hi-Res colors appears as fringing on a
standard Hi-Res image--at least on my ROM 3, been such a long
while since I looked at my ROM 01's (e.g. a pixel to the left or right
might be yellow, red, brown, etc--colors that have no business being
in Hi-Res).
All color on an Apple II is, in fact, "artifact color", but the blending
and fringing you see are the result of rapid transitions between
artifact colors that exceed the chroma bandwidth of an NTSC monitor.
-michael
AppleCrate II: An Apple II "blade server"!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."