Re: Optical Density ?
Re: Optical Density ?
- Subject: Re: Optical Density ?
- From: "John" <email@hidden>
- Date: Thu, 5 Sep 2002 08:31:00 -0400
>
On 9/4/02 6:42 AM, "David Harradine" <email@hidden> wrote:
>
> I'm just wondering about scanners that claim dynamic ranges or even
d-max's
>
> higher than 4. As I understand the optical density scale there is no
denser a
>
> d max than 4. Is there a different scale for scanners to that of
traditional film
>
> measurement ?
Although most CCD scanners claim high d-max reproduction, in reality this is
still their shortcoming. We run both high end flatbed CCD units and drum PMT
units. Although most of our work is now done on the flatbeds, the problem
subjects, especially the very very dark transparencies need to be drum
scanned. It is rare to find a transparency with a shadow d-max in excess of
3.6 and most run in the 2.8 to 3.2 range. (remember we are talking shadow
area, not the sprocket holes). However even with these "low" numbers, the
drum has the superior edge with shadow detail. Without having a drum scan up
on your monitor along side a flatbed scan of the same subject, it is
impossible for anyone to look at a single subject flatbed image and evaluate
where the shadow detail starts to fall off. Just because some specks of
detail is shows in a shadow area, doesn't necessary mean your scanner is
really doing the job it should be.
John
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