What's with this "Shoot to the right"

Started Nov 24, 2010 | Discussions thread
Detail Man
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A Case of the Impracticality of "ETTR" with the DMC-LX3
In reply to Barrie Davis, Nov 26, 2010

Barrie Davis wrote:

Detail Man wrote:

... it is essential that linearity (in the transfer functions of the individual photo-sites, the read-process, and the A/D conversion) is maintained. My own attempts to implement "ETTR" with the DMC-LX3 image-sensor and system revealed photo-site non-linearities that begin to compromise accuracy of highlight-details at levels as low as one EV below the "raw" clipping point.

So, not a big success for you then?

Correct. The DMC-LX3 image sensor appears (when using Center-Weighted metering mode) to have (only) around 0.5 EV "RAW headroom" past the (JPG) "clipping" levels.

This is in contrast to dSLRs, which are reputed to (typically) feature more on the order of 1.5 EV of "RAW headroom" past the (JPG) "clipping" levels.

After I managed to "re-calibrate" my "Live Histogram" closer to the actual "raw" clipping-points (with LCD previews and recorded JPG being a very intense and ugly Green-ish hue as a result of accomplishing the "re-calibration"), I found (as shown in the Ricoh Forum posts previously linked to by me on this thread) that there were significant (and un-recoverable ) highlight-details being lost in the kind of finely-detailed, low color-contrast subjects that I like to photograph (such as the fine structures of moss).

As a result, I ended up dropping the attempt to "ETTR" with the DMC-LX3 (using a "UniWB" Live Histogram calibration scheme) altogether ...

Have found that to completely avoid such losses of highlight-detail in the kind of finely-detailed subject-matter that I like to shoot, it is necessary to (in Center Weighted Metering mode) restrict the "bulk" of the lit-up "dots" in the "Live Histogram" display to around 70% of full-scale (around 0.5 EV below absolute maximum on the normal "live Histogram" display, and around 1.0 EV below the RAW clipping limits). I use this same "rule" for the RW2 as well as the JPGs that I simultaneously record. I use the JPGs simply for sorting, and process the best RW2 image-files.

My approach is to shoot with the lowest possible ISO Sensitivities and avoid the potential nightmares of blown-highlights that no tone-curve adjustments or "highlight preservation" schemes can (in my experience) often reliably remedy to my satisfaction. If that limits the amount that I am able to "raise the shadow-tones", so be it. I would rather have an image to work with that is not un-recover-ably compromised by blown highlight-details.

Whereas I find (from viewing their images on a Histogram) many users often appear to "flirt with the edge of clipping" rather brazenly (resulting in significant levels of "clipping" on some or all of the color-channels), the floral/nature/landscape subject-matter that I like to shoot (in my view) does not take well to such liberties.

I tend to most often work in within a more limited (subject-matter) tonal-range (without direct skylight, or first reflections of direct sunlight) in late afternoon or early evening light (or every once in a long while, early morning light). The Tonal Range of the DMC-LX3 simply is not up to (linear, non-clipped) representations of higher dynamic-range scenes ...

The moral of this story may well be that medium sized (around 1/1.7") image-sensor cameras appear to push the limits of photo-site linearity rather brazenly in an attempt to "squeeze out" every possible last EV in their specification numbers.

It appears that "ETTR" is much better suited to cameras with larger pixel-sizes (such as DSLRs) that provide a more significant amount of (linear) "RAW headroom" over and above the JPG clipping-levels. Ironically, the F-Numbers required in such lens-systems are typically significantly higher, and it falls upon longer Shutter-Times to increase the Exposure-Levels, and/or higher ISO settings to boost "signal" levels towards the maximum input levels of the digitizing A/D converter ..

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