When would you use 14bit over 12bit?

Started Sep 21, 2007 | Discussions thread
Bill Janes Senior Member • Posts: 2,032
Re: Not quite true

Ed_C wrote:

I can't imagine too many times that 14 bit would be a significant
benefit for a wedding shooter. In the old bride in white, groom in
black & white those two should get the most attention and 14 bit
isn't helping them so much. It MIGHT show some more subtle shades in
a horrible brides maids dress or some flowers.

The extra two bits could give an extra two stops of dynamic range, which could be quite helpful in capturing the white of the bride's gown and the black of the groom's tux. Depending on the quality of the analog to digital converter, this extra dynamic range might not be realized. For more details, see Roger Clark's web site, figure 8a and the accompanying text:

http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary/

Ethnic weddings could be one such case though. Indian weddings, etc.
with lots of rich colors might benefit but in all reality probably
not enough to warrant the extra disk space.

What you gain in 12 bit vs. 8 bit is more subtle gradations of color
... same for 14 vs. 12 bit. A rich Fall landscape might benefit.
Really any landscape. The extra depth might be handy for advertising
shots.

You seem to think that extra bit depth gives more shades of color, but for that I think you need a wider color space, such as ProPhotoRGB. The extra bit depth will give more potential dynamic range and less posterization, and 16 bits are generally recommended for wide spaces such as ProPhotoRGB or LAB, but some experts (e.g. Dan Margulis) question this. With insufficient bit depth, posterization occurs principally in the shadows, where there is little perceived color. For a good discussion of the number of tones in each f/stop of the dynamic range, see Norman Koren's discussion:

http://www.normankoren.com/digital_tonality.html

The thing I still haven't seen is if there are any mainstream or
output devices that will reproduce the extra colors you are
capturing. If you can't print it it certainly reduces the point of
capturing it.

Traditional theory was that it helped you when heavily manipulating
files in Photoshop ... potentially reduced posterization, nicer
combless histograms. Now there are some VERY respected Photoshop
gurus who say it isn't even a big deal to just stay in 8 bit through
the entire workflow.

What you say applies to the final output referred rendering of the image into a gamma encoded space, where 8 bits is generally sufficient (but barely--see Norman's discussion). For raw capture, which is linear, 8 bits would give severe posterization in the shadows. Again, refer to Norman's table in the quote.

For scene referred encoding of high dynamic range subjects, even 16 bit integers are not enough and high dynamic range (HDR) encoding requires floating point or logarithmic encoding as Greg Ward points out:

http://www.anyhere.com/gward/hdrenc/hdr_encodings.html

These scene referred images must be compressed down to something that can be printed or viewed on a screen, a process known as rendering. The scene might have a luminance ratio of 100,000:1, whereas the print can have a ratio of only 250:1 or less. This is explained very well by Karl Lang in a white paper on the Adobe web site; see the section "The Big Squeeze". In the process, Karl explains scene and output referred spaces:

http://wwwimages.adobe.com/www.adobe.com/products/photoshop/family/prophotographer/pdfs/pscs3_renderprint.pdf

The same considerations apply to very wide color spaces such as ProPhotoRGB. You might not be able to see or print all the colors that have been captured, but you can control how the out of gamut colors are rendered into a narrower gamut of the printer or screen. If your bride has very colorful accessories, you probably should use ProPhotoPro and 16 bits Also, you are covered when better output devices become available.

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Bill Janes

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