From: George Taylor <George.Taylor@msvu.ca>
Newsgroups: comp.emulators.cbm
Subject: Re: A true C64 video emulation...
Date: Fri, 21 Mar 1997 10:56:38 -0400

I think there are 3 separate topics here:
1) A 'bug' of TVs, is that very hires pixels may hit only part of the
phosphor triplet, thus causing colors not intended.  This has been used
in many programs, including Atari 800 and 64.  On my 1084 with direct
connection (s-video) to the 64, I cannot get this effect.
2) Interpolated scaling on PC.  On some video cards which support it,
you can scale a lores window to the full size (ie, 320x240 to
1024x768).  When the pixels are enlarged, they are interpolated, and
antialiased, which causes some other shades than the originals to
appear, and a sort of blurring effect between pixels.  This has nothing
to do with #1.
3) Bleeding of colors due to limited bandwidth YUV encoding.  This is a
limitation of a TV signal (including s-video), where the color
resolution is limited, in fact less than the 'brightness' portion.  For
example, you can see 320 pixels from the 64 in b/w, but only 240 or so
in color.  Therefore, if two hires pixels, blue and red are together,
the blue from the first will overlap by 1/3 with the red from the
second, and this effect is easily observed.  By the way, try the colors
light green and dark green together.  They have the exact same color
value, but only varying in brightness, therefore they have no bleeding
and are very high quality!  This is also why the default colors of the
64 are blue, and why the charset has 2 pixel wide stems.

To create the effect of #3 (and #2 if desired), load 64 screen snapshot
(from an emulator) into photoshop.  Change to Lab mode, then add blur to
the channels a and b.  This is similiar to limiting the bandwidth of the
chroma signal.  You can also resample/zoom the pic to similate the
effect in #2.  The effect #1 probably depends on your TV so it's not
very possible to do.

I am working on some projects with color calibration and picture
conversion, and am thinking of adding a way to simulate flash colors and
color bleeding to 'improve' the quality of converted pics.
