Posted by Ed Anson on 07/02/06 22:52

PTravel wrote:
> I was thinking more in line with the video equivalent of an audio
> compander -- something that can take the limited range that's available and
> expand it. For example, if Na lights put out light limited to 240-245
> angstroms (I'm just making up numbers here), something that would
> extrapolate on the video so that the lower range fell closer to red and the
> upper range closer to blue would provide a more varied, albeit false,
> coloration.

You appear to be working against physics.

According to Wikipedea (http://en.wikipedia.org/wiki/Sodium_vapor)
"These lamps produce a virtually monochromatic light in the 589 nm
wavelength. As a result, objects have no color rendition under a LPS
light and are seen only by their reflection of the 589 nm light."

Filters work by removing light at unwanted wavelengths. Given a
monochromatic light source, no filter can do anything but reduce the
intensity of what is there. Even if the light were simply a narrow
spectrum, you would need special sensors to do what you suggest. You
certainly couldn't do it with a normal camcorder.

I'd be inclined to go with the monochromatic effect. You can replace the
sodium color with any tone you want, and produce a pleasing image. But
there's no way you can get a polychromatic image using monochromatic light.

>
> Hmmm. Have I just invented a new filter?

[Back to original message]