Mr. Clark:
I usually just lurk, but I wanted to say "Thanks" for your clear and
detailed explanation, plus the great examples. I appreciate you taking
the time to work through these examples, and to publish your results.
It clearly took significant time and effort - and I benefitted from
it.

While my focus is much less on the technical details at this level,
and more on the creative process and results, having this information
available from a non-vendor helps me make better choices about the
tools and techniques I choose to use. You confirmed and clarified
things I've been learning the hard way after switching from
transparency film to digital.

We are fortunate to have both the technical and the artistic
tempraments available to us on the web! What a great combination!

Thanks and best regards,
Art

PS - If you ever have the time, I'd really value a comparison of the
Open Source UFRaw converter against the Photoshop ACR CS4 converter.
With many of my friends and colleagues using it, as well as myself on
my field gear since Photoshop licenses are not cheap, I'd really like
to know the technical differences and capabilities.




On Fri, 07 Aug 2009 23:56:27 -0600, "Roger N. Clark (change username
to rnclark)" wrote:

Digital Dynamic Range and Exposure Latitude

Well, I stopped by here for the first time in a year or so.
I see not much has changed.

But in case anyone is interested in some data and images
that illustrate what digital and film can do regarding
dynamic range and exposure latitude, I offer the following.

A big problem with film versus digital and what each
can deliver is that published data are different for the
two technologies. For example, film's characteristic curve,
which looks great, is measured with a 48-micron diameter
spot (that would be about 60+ 5-micron DSLR pixels averaged).

So I tried to measure each with close to the same sampling.
For example, 4000 ppi scanning is a 6.3 micron spot
size, similar to DSLR pixels (in practice the scanner resolution
is not that good, so the result is slightly larger pixels, which
would be closer to a high end DSLR).

Here is one comparison, with images:
Figure 5 compares digital 16-bit, digital jpeg,
print film and slide film:

Dynamic Range and Transfer Functions of Digital Images
and Comparison to Film
http://www.clarkvision.com/imagedetail/dynamicrange2

Then see Figure 8B for characteristic curves of 16-bit digital,
print and slide film. Note how the film loses it in the shadows,
just as the images in Figure 5 show.

What the curves and images don't show is on the print film
you can recover further into the highlights with some different
scanning techniques that I developed after I did this page.
Trying to recover those highlights on film does result in
increased noise and color shifts but at least you can go higher
than digital.

Next look at:
The Exposure Latitude of a Digital Camera
and Comparison to Film
http://www.clarkvision.com/imagedeta...ure_latitude-1

Figure 1 shows the noise analysis of print film and digital. I still
have more points to measure on the film, but I got some of the
high end ones to show how far up the film goes (again with color
shifts).

The images show digital can produce very good images over the
range of +2 to -5 stops and show image detail over 15 stops.
Other digital cameras and meters may shift this up or down,
but should have a similar range.
Yes this can be done with a 12-bit system because you have many
pixels where your eye averages the noise, much like it averages
film grain.

The bottom line is that digital produces better shadow detail,
and print film goes much higher in the highlights. One just
needs to learn to expose the two differently. But their total
range is similar. Slide film is less than both.

But there is more to the story. To achieve the large dynamic range
with digital, one must use raw data and do a good 16-bit conversion
(or 32-bit) with software that can deliver those results.
Not all raw converters do a good job in this regard.
See:

Digital Camera Raw Converter Shadow Detail and Image Editor
Limitations: Factors in Getting Shadow Detail in Images
http://www.clarkvision.com/imagedeta....shadow.detail

I'll close with a high dynamic range image done with a single
exposure and one raw conversion. This was a tough image to acquire
and I exposed it to not over-expose the area around the sun. The
foreground was very dark in the converted image and the dynamic
range had to be compressed a lot to show the range of the scene:
http://www.clarkvision.com/galleries...867.c-800.html

So, good digital cameras with large pixels have a huge dynamic range,
comparable to print film, but shifted to the low end, and digital
has much higher dynamic range than slide film. Note also that DSLRs
will maintain high dynamic range to higher ISOs than film.

Roger