Tom Nelson

In article <SPvXa.63741$uu5.6238@sccrnsc04>, Leonard Evens
<len@math.northwestern.edu> wrote:

> Photoshop starts with values in the range 0..255 (for each channel)
> obtained from some source. That source could be a digital camera or
> more likely in your case a scanner used to scan the Xray film. One
> would have to know just what that device is doing in creating the values
> 0..255. For example, Vuescan used in conjunction with one of the
> standard film scanners can actually show what Ed Hamrick tells us is the
> density of the film at each point in the scan. I haven't checked
> with a densitometer to see if his values are accurate, but they
> certainly seem to be in the right ball park of what I would expect. But
> his software, as does any scanning software, converts the density values
> to RGB values in the range 0..255. How it does it depends on some
> parameters, including the white and black points and a value of gamma.
> Since the aim in scanning is to get a usable image, whatever the density
> range in the source, it is going to be difficult to relate the latter
> values to density.

Most scanning software allows you to save scanning parameters. Might
you prepare a slide with the maximum possible stain next to an
unstained area? You could relate those densities to 0 and 255,
respectively, and use that setting for your test slides.
Tom Nelson
Tom Nelson Photography