I did not mean to propose that an effective ETTR solution is totally
simple. And I think dragging in most of the digital camera market into
the discussion is not relevant. Most of the digital cameras sold today
don't have spot meters either. I would expect to see an ETTR feature on
professional cameras, not P&S.
I accept that it probably cannot be totally automated such that it fits
all situations. The main point is that the camera has far more
information than I do and is not making good use of it. At the very
least it could tell me what percentage of pixels are clipped.
Chuck Norcutt
On 12/3/2011 6:27 PM, Moose wrote:
> On 12/3/2011 4:50 AM, Chuck Norcutt wrote:
>> Your struggles with the exposure foibles of the E-1 reminds me of an
>> article I read recently chastising our camera designers for not making
>> full use of the exposure measurement technology already available to
>> them. It covered more ground than ETTR but, since ETTR is of special
>> interest to me, it's what I paid most attention to. The author simply
>> pointed out that any camera with live view could easily implement an
>> ETTR exposure mode and guarantee that no highlights would be blown since
>> it knows the exposure state of every pixel.
>
> It seems to me that the author's view is simplistic. Implementing auto ETTR
> in-camera is trickier than one might
> imagine. Let me give examples:
>
> 1. When scanning film with VueScan, it is possible to do exactly what he
> proposes. Simply set White Point to 0 and VS
> will expose/process so that the highest brightness in any channel of any
> pixel is defined as the top value in the scan.
> So nothing is clipped. (Same choices at the bottom)
>
> With some frames, this works just fine. With frames that have just a few
> points exposed much above the rest, it tends to
> underexpose the image as a whole, sometimes very seriously so. A WP value of
> 0.01% is often enough that overall exposure
> is good and there is no visible clipping. I've never seen any visible
> clipping at 0.1% or even higher.
>
> 2. When editing an image in PS that has small, specular highlights and an
> overall histogram that just kisses the top,
> select a small area with specular highlights and check its histogram. Oops,
> clipped values! This is essentially the same
> problem as in example 1.
>
> 3. When editing subjects like water rushing over rocks in direct sun, I
> usually work to avoid blown highlights. Quite
> often, once I've carefully dealt with them, and have a 'perfect' looking
> histo, I realize that the image now looks less
> appealing than at an earlier stage. The truth seem to me to be that for some
> subjects/circumstances, a modest amount of
> clipping in the right places simply looks better.
>
> Now some bits of information:
>
> 1. Since the beginning of photo processing for consumers, prints were made
> with intentionally contrasty midtones and the
> highlights and shadows allowed to clip. The reasons are simple.
>
> a. The average camera user/print consumer preferred punchy snaps to
> flat ones with broader dynamic range.
> b. Even with the latest computerizes processing, it wasn't practical to
> custom tune individual images to the needs
> of the subject.
>
> 2. Things haven't changed that much with digital. The vast majority of
> cameras sold, and thus those from most of the
> profits are made, are judged by the images that show up on their LCDs or on
> prints from automated machines. People go
> into the shop, snap a few shots on the demo and judge the camera based on
> what they see on the LCD. Or they look at
> sample images on the web.
>
> There has been improvement. Quite a few cameras now include algorithms to
> evaluate characteristics of subjects to select
> exposure and internal processing parameters. These filters are based on
> analysis of at least thousands of shots of
> common subjects. The smart auto mode on the Sammy WB650 is far better for a
> shooter like Carol than simple auto the Fuji
> F10 she was using before. I, on the other hand, get about the same sort of
> results with either F30 or Sammy.
>
> So here's the dilemma for camera makers who might want to include auto ETTR:
>
> On one hand, their ability to produce images that will please the buyers of
> the majority of their cameras without
> clipping highlights a lot of the time is still limited. ETTR isn't practical,
> or at least doesn't add perceived value to
> consumers.
>
> On the other, the technically sophisticated photographer is likely to find
> any particular implementation of auto ETTR
> parameters to fall short with too many subjects:
>
> 1. Set WP to zero, and too many shots will be seriously underexposed. Then
> when the midtones, and especially the
> shadows, are pulled up to balance the image, noise rears its ugly head.
> Unhappy users!
>
> 2. Set the WP too high, and another (probably overlapping) bunch of users
> will be unhappy with the clipping.
>
> There are also technical limitations:
>
> 1. The vast majority of mirrorless cameras using live view probably don't
> have the processing power to implement auto
> ETTR as proposed without slowing them down to unusable levels of performance.
> Even high end compacts and most ILCs are
> not rockets in performance already. Add the requirement to evaluate 10-20
> million individual pixels in real time to set
> exposure - not with current price/technology.
>
> 2. Live view on DSLRs is not the primary mode of use for most shots, for most
> people. I love live view, but it still is
> probably used for no more than 10% of my shots. And it is, of course,
> impossible to do live, auto ETTR with the mirror
> down. (Maybe with an E-300/330 hooked up to an external computer?)
>
> 3. For a great deal of live view uses, live histograms, bracketing, chimping,
> etc. are quite practical ways of
> controlling ETTR.
>
> When will we see auto ETTR? When a significant maker adds it as a feature and
> promotes it as their unique advantage. If
> it then catches sales, everybody will add it, whether it is actually useful
> and/or works worth a darn or not.
>
> What are camera makers doing to address the need to minimize clipping today?
>
> 1. "Smart" scene modes are working their way up into lower level DSLRs. I've
> never used them, but I think the 60D has
> such a thing. I believe the same is true for other makers.
>
> 2. I haven't kept up with all the endless DSLRs out there. I do know the D60
> has a mode that modifies the shoulder of
> its response curve to have a much shallower roll off - and up to a higher
> level of subject brightness, than the standard
> setting. In effect, it compresses the highest tones, rather than clip the
> very highest. Given the very large number of
> value steps available at the top of a 14 bit image, this allows much greater
> recovery of highlight details in post.
>
> The price is a minimum ISO of 200, and the slightly higher shadow noise of
> 200 vs 100. Overall, I have found it pretty
> effective in extending practical DR and guarding against unintentional lost
> highlights.
>
> It directly addresses the issue you raise with the 5D, of setting ETTR using
> the histos, and still having some clipping.
> The 5D is a great camera, but pretty old technology in some areas.
>
> Technically Wordy Moose
>
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