[APML]: Scanners (was Digitizing Slides...)

[aa6g@aa6g.org (Chuck Vaughn)]

>Even on tech pan, would they not do better than a flatbed?  I have a HP
>ScanJet 3p, which is just 256 grey scale, no colour scanning.  It cost me
>the same price that a lot of "no-name" colour flatbeds go for around
>here.
>($600.oo CDN)
>
>    What I find though is you still lose a lot - especially in shadow
>detail.  Would you not avoid that problem scanning right from the neg?
>
In regards to shadow detail; the SprintScan 35 scans 10 bits but outputs
8 bits so you still only have 256 levels. If you have to use the entire
3.0 dynamic range to show your object then the 10 bits doesn't do you
much good, you can't take advantage of the 1024 gray levels. On the other
hand if your negative has a dynamic range of less than 3.0 and a max density
of less then 3.0 then you can set the black and white points to cover a
smaller range and still have 256 gray steps which should equate to better
shadow detail. Hopefully that makes some sense.

One problem I have with my scanner is that the scans tend to look "stepped"
at the black end of the range. I find I can mitigate this look somewhat if
I scan the negative so that the first 10 or 15 gray values have no pixels.
That is the darkest pixel value is around 10 to 15 instead of 0 to 5. The
tradeoff is that the background is not as dark.

The new scanners are 12 bits and claim a dynamic range of 3.4. You still
only end up with 8 bit grayscale because that's all Photoshop and any video
card I know of can handle.

Interestingly enough, the Macintosh operating system supports 48 bit color
but nobody takes advantage of it. That would be great because you could
display 16 bit grayscale and take advantage of the FITS format directly.

Chuck Vaughn
<aa6g@aa6g.org>