Re: Dana's children's art project
Re: Dana's children's art project
- Subject: Re: Dana's children's art project
- From: Bob Ware <email@hidden>
- Date: Wed, 08 Aug 2001 18:06:57 -0700
I dont know that you are going to be able to solve the problem of
specular highlights from scanned artwork with impasto surfaces or
pearl surface photographic papers in your scanner. You have correctly
identified the problem as stemming from the uneven texture of the
scanned surfaces. The multitudinous family of angles such surfaces
present cause many small areas to directly reflect the scanner lamp onto
the receptor chip just like the blinding reflection of sunlight on the
rear window of the automobile in front of you; the ever-changing angles
of reflection in the curved car window mean that somewhere across its
surface is likely to be a direct, efficient angle between the sun and
you.
Simply re-photographing the material will present much the same problem
unless you polarize the light source(s) and the camera lens. To do this,
you will need a lamp (or two, placed equally to each side of the artwork
[roughly 450] for even illumination across the artwork) housed in a
reflector. For color photography you will need to match the color
temperature of the lights to your film, typically 32000 Kelvin photo
flood lamps and Tungsten film, or you will experience unwanted color
shifts. You can then mount a piece of polarized plastic across the light
path, close to the lamp, but sufficiently far away to allow for heat
dissipation. Professional camera stores can sell you sheets of this
polarizing film. Unfortunately, its expensive, but if you take care of
it (as in, dont melt it) it can be used over and over. The polarizing
sheets over the lamps must have the same linear orientation. Typically,
one cuts the individual sheets out of a larger sheet, and if you take a
marking pen and indicate one common UP edge before you cut them out of
the larger sheet, you will always know how to orient them. Then, if you
place a screw-on polarizing filter on your lens, you can rotate it to
minimize glare everywhere across the artwork (suggest you buy a
circular rather then linear polarizing filter, as the circular type
will allow accurate meter readings with all cameras, whereas the
majority of modern cameras can have trouble with linear polarizers;
there is no practical difference in the picture-taking qualities of
these two types of filters). Each layer of polarizing filter adds a
little bit of green to the shot, probably not enough for the average
person to notice, but if you want to do it right, you might consider
placing a .05 magenta filter on your camera lens in addition to the
polarizing filter to neutralize the green shift. You could also use the
more commonly available 1B camera filter, as this has about the same
amount of magenta tint to it. Or you could simply create and save a
Photoshop levels or curves adjustment that neutralizes the green, and
apply this uniform correction to all your images). Plan on a fairly slow
shutter speed, and use a tripod to steady the camera.
If you have access to a digital camera, you can use the same technique
on it and at least save yourself the cost of film and some of the
scanning time. You may also be able to balance the cameras white point
to the light source and get away with some inexpensive painters lamps
from Home Depot. Good luck with the project.
--Bob Ware