October 23, 2014, 04:40:45 AM

Author Topic: Better Dynamic Range in a Camera  (Read 5670 times)

TrumpetPower!

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Re: Better Dynamic Range in a Camera
« Reply #15 on: February 19, 2013, 10:10:04 AM »
Is this what you feel at the edge of the grand canyon on a partially cloudy day? "Ouch, too much dynamic range"?

Yes, exactly. Why else do you think people squint, shade their eyes with their hands, or wear sunglasses or hats?

Quote
Where I am sitting right now, I can watch a bright snowy landscape out of my windows, or peek at my interior in the shade.

And I'll bet that you're squinting at the snow, and, after a bit of squinting, you can't see a bloody thing around you inside. Or else the glass is tinted.

There are certainly times when the point of art is to make people uncomfortable, but those are exceptions. And, even then, the discomfort is almost always toned down or somehow simulated or made distant. Very few people would be interested in a sunset photograph of a beautiful scene that made them squint and shade their eyes, as much as they might enjoy being in the actual setting where the photograph was made, painfully bright light and all.

Cheers,

b&

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Re: Better Dynamic Range in a Camera
« Reply #15 on: February 19, 2013, 10:10:04 AM »

Hector1970

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Re: Better Dynamic Range in a Camera
« Reply #16 on: February 19, 2013, 12:04:37 PM »
Wow the answers are getting even better and more detailed.
When I look at a scene I often can see the bright and the dark and not lose detail in the bright or the dark.
When I take a photo of the scene depending on where it's metering it might make a photo too bright or too dark (losing detail in either case). It might also (if I meter correctly) do a kind of average where I lose some detail in the bright and some detail in the dark.
The dark bit I might dodge and the light bit I might burn (or use a lightroom filter).
Could a sensor have dark but retain all the detail (ie it's not black unless it  is black) and bright light but also retain all the detail (it's bright but not completely white)?
Then there would be no need to dodge or burn or use filters.

I suppose in the end a photographer is trying to capture what they see (or at least what they think they see).
The photo is often under or overexposed or both.
In their chase of more expensive equipment (bodies, lenses, filters, software) they are trying to combat these possibilities.
In the morning or evening light the dynamic range is less and they can capture the scene with their sensor.
By midday this possibility may be gone.
Could it be possible to capture this by camera and lens alone by a magic sensor which captures the scene as an eye would?
By the answers so far it doesn't seem to be so easy to do.
Maybe the eye fools us because it is all the time processing the information to show us all the scene.

TrumpetPower!

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Re: Better Dynamic Range in a Camera
« Reply #17 on: February 19, 2013, 01:17:36 PM »
When I look at a scene I often can see the bright and the dark and not lose detail in the bright or the dark.
When I take a photo of the scene depending on where it's metering it might make a photo too bright or too dark (losing detail in either case). It might also (if I meter correctly) do a kind of average where I lose some detail in the bright and some detail in the dark.
The dark bit I might dodge and the light bit I might burn (or use a lightroom filter).
Could a sensor have dark but retain all the detail (ie it's not black unless it  is black) and bright light but also retain all the detail (it's bright but not completely white)?

Let's put some numbers to the question to help things along.

We'll start with a carefully controlled environment -- a viewing booth with a standard D50 illuminant. That would be a full-spectrum daylight-balanced light source that's reasonably bright at the print. A light trap (a hollow black-lined box with a small hole at the top) would be 0. A piece of Teflon thread tape would be 100 (or close enough as makes no difference. A piece of high-quality fine art paper would be just barely discernibly darker, around 98 or 99. The darkest you could print on that paper would range from 10 or so to 20 or so, depending on the actual paper and printer.

That's basically what the L* value represents in the Lab color space -- except, of course, the definition is more precise than what I just gave.

Unlike RGB color spaces, the Lab space is open-ended. Most real-world scenes contain images with considerably more than an L* value of 100.

For example, right next to this standard light booth, let's place another one with the print raised so it's closer to the light source. It's the same piece of paper as the one in the standard booth, but it's now more brightly lit and so, to the observer, has an L* of more than 100. How much more depends on how much closer the paper is to the source, but let's pick an arbitrary number and say it has an L* of 150.

You're standing there with your high dynamic range camera and you take a picture of this very scene. Not a problem -- the camera captures it just fine.

But now what're you going to do with that file?

If you want to make a print, the stuff in the standard viewing booth is no trouble; with the proper workflow, within certain limits, your print can look identical. The picture of the bare paper gets no ink in your print, either, and the other parts get the same ink as in the original.

But how are you going to make the image of the paper in the non-standard booth be brighter than the paper in your print? That is, with a paper that has an appearance of L*=99 in standard viewing conditions, how are you going to make an image of something that has an appearance of L*=150, and still show the image in standard viewing conditions?

There are a few possibilities.

You could compress the captured dynamic range. The image of the paper in the brighter booth would get printed as L*=99 (you have no other choice), and everything else gets similarly scaled by 2/3. The image of the paper in the standard booth gets printed as L*=66, which is roughly Zone VI.

You could be more gentle in your compression. You could print the paper in the brighter booth at L*=99, print the paper in the standard booth at L*=90, and thus make the standard booth look very close to as it was but everything in the brighter booth would look very washed out.

You could go ahead even further and clip everything in the brighter booth that happened to wind up brighter than L*=99.

You could do some masking and render each booth to a normalized version, such that the white paper in the standard booth got rendered as L*=99 and the white paper in the bright booth also got rendered as L*=99...but what're you going to do in the space between the booths? And you're now left with the two booths looking the same when they were significantly different to your eye.

One obvious solution would be to not make a print of the scene but rather to show the scene on an illuminated display. Let's say that this display can go from L*=5 to L*=200. Now, there's no problem showing the full scene that originally went as high as L*=150. But now you might have a different problem...the viewer's eyes might be adapted to thinking that L*=200 is "full bright," and the L*=150 parts of the scene in the original give the appearance of being less bright than they actually were. You then might be tempted to scale everything the opposite direction, to make L*=150 map to L*=200...but now either you also have to raise the blacks and make them washed out, or you wind up stretching the dynamic range overall and creating more contrast than there originally was.

Now, instead of simply two viewing booths with slightly different light levels, imagine you're also including the lightbulb itself in your scene. That may well be L*=1000; how are you going to reproduce that?

So, sorry, hate to break it to all y'all, but we're never going to stop having problems with dynamic range in photography.

Indeed, it's the exact same problem as artists everywhere have always faced...and that's why artists are always talking about the light, why there exists such things as good light and bad light.

It's all about the light. It always has been, and it always will be.

Cheers,

b&

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Re: Better Dynamic Range in a Camera
« Reply #17 on: February 19, 2013, 01:17:36 PM »