Greyscale Mode Test for the PCE
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by Chris Covell (chris_covell@yahoo.ca)

This demo displays over 100 shades of grey on the PC-Engine/TG-16, which can normally
only show 8 levels of grey, including white and black.

How is this possible?  It uses the greyscale mode bit of the VCE (bit 7 of $0400)
to remove the colour from images.  I did a few tests using this B&W mode to see if,
while removing colour, it simply mapped images to its regular 8 shades of grey, or 
whether it did a more complex averaging of the colours, taking the luminances of red,
green, and blue into account.  It turns out that the latter is true, giving many
shades of grey when this image is output to a TV.

However, some TVs don't like the video output of the PCE in this mode.  It seems that
the brightness level of the image is OK, but the colour component is either missing, or
incompatible with the NTSC standard.  It's hard to tell what the PCE is doing, but clearly
it's not a true simple B&W signal.  Furthermore, this B&W mode doesn't work on the
TurboExpress or PC-Engine GT systems; they still display the colour versions of my pics.
Needless to say, this can best be described as a dirty hack.

In the demo, press the I button to advance through the 4 pictures.  So far, no emulators
are able to display the greyscale mode, so you will just see some pics with wild colours.
It only looks as it should on a real PCE/Turbo system.