rak@crosfield.co.uk (Richard Kirk) (06/21/91)
Consider the following common page make-up problems...
Suppose you have a scanned picture of a bottle with a label on. Suppose
also you have another design for a label. You want to replace the old
label with the new one.
Suppose you have an image of a jacket made with one fabric. You wish to show
what it might look like when made with another fabric.
You have an image of a jersey. You wish to make the jersey look a different
colour. However the appearence of an overall colour is the average of the
light paths within the wool that have reflected once/twice/three times off the
dyed material. How do you recolour the image at high resolutions?
You have an object. You want to plonk it against an artificial background.
You need to generate an artificial shadow. How it that done?
In all of these cases we only start with 2-d image information so we cannot
come up with an exact ray-trace results. But we do not need an exact solution:
all we want is something that looks convincing. This usually involves some
guesswork.
Take the example of the label on the bottle...
(a)
An operator could rubber-band a 2-d bezier spline onto the label on the
bottle by eye, the put the same distortion on the new label. The new label
will have no shading or highlights, but these can be brushed in later.
(b)
If we assume the original label has not stretched, we can guess the 3-d
shape from the 2-d Bezier coefficients. If the original image had a ball
bearing we could get an angular map of the light fluxes, and so to a ray
trace.
(c)
We could stick a white label with a black grid on the bottle. We could
then get the 2-D distortion, the shading and the highlights directly from
a known source. It would then be easy to superimpose the densities of the new
label on the white regions of the old one.
In my experience method (a) is what a retouch studio would do; (b) is
not contemplated; (c) is possible but usually there is no nice studio shot of
a bottle with the label you want to hand.
Is there anyone out there in Newsland who has experimented with this sort of
thing and come up with a (b), (c) or (d) solution that might compete seriously
with the skilled image retoucher (a) for speed and quality? Or failing that
is there anyone else who wants to share the development of such a system?
--
Richard Kirk Image Processing Dept Crosfield Electronics Ltd. U.K.
0442-230000 x3361/3591 Hemel Hempstead, Herts, HP2 7RH