subliminal color images

[Dave Long]

> It would be cool to print out a black-and-white image on, say, a laser
> printer, which contained an unobtrusive embedded "watermark" or
> "barcode" that contained chroma information for the image --- rather
> like what the Apple II did to get NTSC color just by producing a
> pattern of 1's and 0's.

This works for NTSC because the color TV people needed to place their 
signal on a backwards-compatible black and white signal, so the I and Q 
information is squeezed into a narrow band just above the Y -- and 
hence high-bandwidth luminance patterns alias into the color range.

Come to think of it, the Apple II scheme turns a well known broadcast 
bug (there are dress codes for on-air appearances, as houndstooth and 
similar high-frequency fabrics alias into color) into a feature.  I 
wonder how much the use of gradients in web graphics is due to 
recent-featurism, and how much is in imitation of broadcast graphics, 
which have to have smooth gradients -- they'd bleed if one tried to 
make a crisp transition.

> Then you could point, say, a cellphone camera at the image, and push a
> button, and see the image in color.

Unfortunately (fortunately?) the information between a cellphone camera 
and a printout isn't mediated by NTSC, but by regular photons, so it 
seems unlikely this would work.

-Dave