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Monday, 28 April 2008

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In the K10D, the Bright and Natural tone curves are much more than just preset values for Saturation, Contrast, and Sharpness. They change the gamma curve for the resulting image, making quite a difference. There's no "Hue" option in the K10D, but it doesn't sound like that replaces the curve exactly either, so I expect that this is actually the case in the K20D too.

Dear Carl,

Again, what is the total exposure range for the camera?

Without knowing the shadow-side range as well, I can't determine the import of the highlight side range, because I don't know where the meter has set the exposure point in the total exposure scale.

pax / Ctein

Re: Expanded dynamic range

Carl,

This is probably just the same thing that other manufacturers are doing with their cameras. Here is a description from DPReview's review of the Fuji S100fs:

"It would appear that - put simply - the S100FS is under-exposing the shot by one or two stops (to preserve the highlights) and applying a custom tone curve pull the other brightness levels back to their correct values.

Another way of looking at this is to think of the highlights as being shot at ISO 100 and the shadows at ISO 200 or ISO 400 since the camera is effectively applying a non-linear gain to the raw output (which inevitably looks very dark if opened in a non-Fuji development application). In effect this isn't that different to the options offered by Nikon (D-Lighting), Canon (HTP) or Sony (DRO)...

You don't get something for nothing, of course. Shooting at 400% [200% for the Pentax] limits you to at least ISO 400 (hence giving an exposure two stops shorter than the camera's base ISO setting), and this does mean the shadows get noisier, though to be fair the results aren't bad at all. If you can live with the additional noise, then it's a useful feature."

See: http://www.dpreview.com/reviews/fujifilms100fs/page16.asp

Best regards,
Adam

Does the “D-Range 200%.” only work for JPEG or does it work in raw as well?

I keep hoping that a camera company will come out with a way to change the linearity of the sensor gain, which would work for RAW as opposed to highlight and shadow masking in JPEG processing which would be nice for people who shoot JPEG , but not much use for me.

BTW, anybody know why tweaking the sensor gain curve at the time of exposure isn't a feature? It really doesn't seem like that difficult a problem.

Matthew, changing the "contrast" setting does in fact change the shape of the gamma curve. Looking at the histograms, I can see it is not analogous to the PS Contrast dialog but more like the contrast slider in ACR, which steepens or flattens the slope and changes the shape of the default curve in a complex manner. Combine this with a shift of Hue and another in saturation (plus a difference in sharpening which will affect the perceptual contrast) and those are all the controls needed to make big changes in the look of the JPEG.

Ctein, as noted in a reply last time, in RAW on default there is still recognizable tone/detail (textured vs smooth target) at -5.7 stops (it reads level 4) though I doubt this tone could be separated from black by any printer. The jpg files seem to track the RAW quite well on the low end. That number is at ISO 100. I'd expect noise to show up with d-range turned on since the ISO setting gets bumped up. To say how far into the shadows it can go needs a judgment call on what level is too black to print, combined with a judgment call on what amount of noise is acceptable, and another on how well, say, detail exposed -2 can be raised to middle. Since I don't have any intention of shooting JPEGs this isn't going to get on my todo list. But the d-range feature definitely does not make the shadow retention any worse, so at modest ISO, there should be at least 5 stops below the meter's middle that at least show clear separation from black and can image a textured surface. On screen.

Adam, I've done some pretty severe rescue work with everything ACR has to offer on files that had to be underexposed to avoid clipping the highlights. There's a look to files that have been manipulated this way. I've also experimented with Adobe's implementation of HDR in Photoshop CS2 and 3 and there's a distinctive look to that (which is similar to HDR examples I've seen from others using different software). The Pentax JPEG files created with d-range look to me much more similar to HDR than to curve-hammering. I don't know what's going on under the hood, just what I see in the files.

Hugh, as noted, there is a slight improvement in highlight clipping point, but it is interesting more because there is *any* impact at all on the RAW file than because the amount of impact is meaningful.

To be pedantic: Those histogram screenshots cannot be directly compared. One has the /!\ alert icon, which means that it's "fake," computed from incomplete data. Clicking the icon will recreate the histo from the full image data.

What in Green Acres are you all talking about?

Chris, not pedantic: technically accurate.

Setting up the damn screen shots from the two files so they'd be viewable in a blog post was not easy. They went through numerous iterations, and at some point one lost the step of clicking to make the hist kosher. For the record, the change in this case is infinitesimal and couldn't be seen in the reduced view anyway. But thanks for pointing out the tech error.

Carl — I don't mean that those settings don't affect curves, but that I don't think it's possible at all to replicate one tone curve mode simply by adjusting the sliders in another one. In other words, that setting does more than just set default levels for the other options. (Much more.)

As a matter of fact, there *is* a slight difference between the two photos, Carl. It might just be my monitor, but your mentioning the highlights in the histogram drew my eye to any possible blown highlights. And there it is, the highlight at the top of the stack of packing tape rolls. The effect is slight but you can clearly see where the detail is saved (the green copy printed on the core of the roll.)

Matthew, I checked again, and you are right that the various modes are doing more than you can get at through the customize settings. Based on the color diagram helpfully provided in the LCD dialog, what they are doing has more to do with saturation and hue (varied saturations and hues for different colors, like playing with ACR's HSL panel) than with the tone curve. These turn out to be "color palette" adjustments as well as gamma curve adjustments.

Now, if only they would offer a "Restrained" mode, we'd be getting somewhere.

The expanded range sounds very much like the highlight protect feature in my Canon 1DIII - and I guess I've come to pretty much the same conclusion. It works in so far as it prevents blown highlights (I figure I can get 2 - 2.5 stops additional overhead), but the price is a degree of unpredictability in the final image quality.

I've played with it a lot, and have decided that it's not acceptable as a default setting, but can be very useful in some conditions - fast action in changing light for example, when there just isn't time to dial in the correct exposure compensation.

It's a sort of security blanket - better to do without it, but when things get tricky, and you only have one chance to get the shot, it may just save the day.

Some people won't like it, some would prefer it wasn't included - but no one says you have to use it, and leaving it disabled has no impact on 'normal' picture taking

Cheers

Colin

Dear Carl,

Thanks for patiently repeating yourself; I missed that information in the comments in the previous column.

So if I understand correctly, there's about three stops range above the exposure point and six stops below. By my standards, I would call that overexposing (as argued in a previous column of mine).

The question that would leave in my mind would be whether the camera is doing anything that I couldn't do in my RAW conversion. I don't know.

I suppose a way to find out would be to make two photographs of a step tablet, one exposed with the d-200 mode and the other "under"-exposed by a stop in normal mode. Pull them both into Photoshop and create a curves adjustment for the latter that matched the tones of the former. Then do some pixel peeping and see if there was any difference in image quality in any of the steps.

If there wasn't, then all the camera is doing is saving me the trouble of creating a custom profile and applying it en masse. Nice but not earthshaking. If there was, that means the camera is doing something cleverer than I can do, and that's a valuable thing.

I believe the Fuji S100FS has a similar feature; when I get my review unit I'll try to run this experiment and see what happens.

Understand that I'm not pooh-poohing this feature; anything that improves average picture quality is a good thing. Just trying to figure out if it's merely nice or really important.


~ pax \ Ctein
[ please excuse any word salad. MacSpeech in training! ]
======================================
-- Ctein's online Gallery http://ctein.com
-- Digital restorations http://photo-repair.com
======================================


Ctein,

Thing is, the camera's middle lands right around the middle of the 255 levels. (Not talking Pentax here, any good digital camera.) But it retains about 5-6 stops of subject luminance in the 0-127.5 levels, and barely 3 stops from there up to level 255. So what's middle? We could dial in -2 compensation to place the range of the scene within the outer bounds of the sensor's reach, but then all the things we want to have middle tone will be underexposed. Grass, blue sky, all will be much too dark and will have to be raised--a lot--in value. Bad enough to take something from Zone III to Zone V in a RAW file, pretty awful with an 8-bit JPEG.

For a long time we got along with the fact that b&w negative films only held full detail for two stops below the meter reading (less if you used the manufacturer's ISO rating) but with carefully tested development easily held detail four or five stops over. Shooting large format film developed in pyro and intended for platinum printing, I can expect to hold full detail at -2, some detail but definite tone separating from black at -3, but on the other end of the scale expect easy retention of bright values at +5 or +6 and above. It's not symmetrical. Color negative film also shows asymmetrical retention of highlight values.

As I've said before, digital capture just turns this asymmetry upside down. I'm much more comfortable with the way negatives do it. That just may be from 40+ years experience with negs and just a few years with digital capture, but actually I think lopsided-to-the-highlights is more like the way we actually perceive things.

I am a Nikon shooter, but I am just tickled pink that Pentax has come out with such a winner of a camera. Cameras like the K20D make things better for all of us, by raising the bar, and forcing everyone else to stay honest. Bravo Pentax, and keep it up!

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