Digicam Challenges

Kirby W. Fong kfong@alumni.caltech.edu
Mon, 15 Dec 2003 19:35:57 PST
Mary Sue Ittner asked if anyone had a good strategy for photographing
white flowers and dark green leaves simultaneously with a digital

I'm just starting into digital photography after a dozen years of
slide photography.  Although I haven't had a chance to try it yet,
I think I understand the problem and what I might be able to do
about it.  The basic problem is that the contrast range is possibly
greater than the medium can record.  Color print film can handle a
slightly greater range than color slide film.  The question however
was about digital cameras where you have to live with the sensor
that's built in.  Most of the sensors actually measure 12 bits per
color or 4096 levels for each of red, green, and blue.  If you
accept the image as a JPEG file, the camera will typically truncate
to 8 bits per color (256 levels).  If you expose the white flower
properly, the dark details of the leaves may be lost.  The solution
I would try is to save the image in RAW or TIFF (not JPEG) format
and acquire it into an image processing application (like
Photoshop) in the 16 bit color mode, thus preserving all the
information that the sensor captured (in particular the dark
details).  Then you can reduce the contrast to lighten up the
dark areas so that leaves and flowers both show details when
you print the image.  This is clearly a lot of work to rescue
one image.  However, you may have an acceptable alternative
depending on your camera.  I've seen at least one digital camera
that allows setting the contrast.  The manual doesn't say what
actually happens, but if in fact it compresses (rather than
truncates) the 12 bit color to 8 bit color, you may be able to
capture both the highlight and the shadow detail.  The
preceding strategies both assume the sensor can handle the
contrast range and that it is just a matter of massaging the
image to show all the details.

My principal interest is daffodils, and I have always exposed
film to suit the flower and let the stem disappear into the
shadows.  Your question has stimulated my thinking about
whether with digital photography I can retain stem detail
along with flower detail.

     Kirby Fong

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