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What is HDR, anyway?

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791 points _kush | 1 comments | 14 May 25 12:46 UTC | HN request time: 0.22s | source
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dahart ◴[14 May 25 16:48 UTC] No.43986653[source]▶
It seems like a mistake to lump HDR capture, HDR formats and HDR display together, these are very different things. The claim that Ansel Adams used HDR is super likely to cause confusion, and isn’t particularly accurate.

We’ve had HDR formats and HDR capture and edit workflows since long before HDR displays. The big benefit of HDR capture & formats is that your “negative” doesn’t clip super bright colors and doesn’t lose color resolution in super dark color. As a photographer, with HDR you can re-expose the image when you display/print it, where previously that wasn’t possible. Previously when you took a photo, if you over-exposed it or under-exposed it, you were stuck with what you got. Capturing HDR gives the photographer one degree of extra freedom, allowing them to adjust exposure after the fact. Ansel Adams wasn’t using HDR in the same sense we’re talking about, he was just really good at capturing the right exposure for his medium without needing to adjust it later. There is a very valid argument to be made for doing the work up-front to capture what you’re after, but ignoring that for a moment, it is simply not possible to re-expose Adams’ negatives to reveal color detail he didn’t capture. That’s why he’s not using HDR, and why saying he is will only further muddy the water.

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munificent ◴[14 May 25 17:54 UTC] No.43987388[source]▶
> The claim that Ansel Adams used HDR is super likely to cause confusion

That isn't what the article claims. It says:

"Ansel Adams, one of the most revered photographers of the 20th century, was a master at capturing dramatic, high dynamic range scenes."

"Use HDR" (your term) is vague to the point of not meaning much of anything, but the article is clear that Adams was capturing scenes that had a high dynamic range, which is objectively true.

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dahart ◴[14 May 25 18:04 UTC] No.43987469[source]▶
Literally the sentence preceding the one you quoted is “What if I told you that analog photographers captured HDR as far back as 1857?”.
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munificent ◴[14 May 25 18:56 UTC] No.43988031[source]▶
Yes, Ansel Adams was using a camera to capture a scene that had high dynamic range.

I don't see the confusion here.

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dahart ◴[14 May 25 19:04 UTC] No.43988110[source]▶
HDR is not referring to the scene’s range, and it doesn’t apply to film. It’s referring superficially but specifically to a digital process that improves on 8 bits/channel RGB images. And one of the original intents behind HDR was to capture pixels in absolute physical measurements like radiance, to enable a variety of post-processing workflows that are not available to film.
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munificent ◴[14 May 25 21:01 UTC] No.43989172[source]▶
"High dynamic range" is a phrase that is much older than tone mapping. I see uses of "dynamic range" going back to the 1920s and "high dynamic range" to the 1940s:

https://books.google.com/ngrams/graph?content=dynamic+range%...

You might argue that "HDR" the abbreviation refers to using tone mapping to approximate rendering high dynamic range imagery on lower dynamic range displays. But even then, the sentence in question doesn't use the abbreviation. It is specifically talking about a dynamic range that is high.

Dynamic range is a property of any signal or quantifiable input, including, say sound pressure hitting our ears or photons hitting an eyeball, film, or sensor.

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dahart ◴[14 May 25 22:02 UTC] No.43989670[source]▶
> But even then, the sentence in question doesn’t use the abbreviation

Yes it does. Why are you still looking at a different sentence than the one I quoted??

HDR in this context isn’t referring to just any dynamic range. If it was, then it would be so vague as to be meaningless.

Tone mapping is closely related to HDR and very often used, but is not necessary and does not define HDR. To me it seems like your argument is straw man. Photographers have never broadly used the term “high dynamic range” as a phrase, nor the acronym “HDR” before it showed up in computer apps like hdrView, Photoshop, and iPhone camera.

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munificent ◴[14 May 25 23:03 UTC] No.43990103[source]▶
Oh, sorry, you're right. Mentioning the abbreviation is a red herring. The full quote is:

"But what if we don't need that tradeoff? What if I told you that analog photographers captured HDR as far back as 1857? Ansel Adams, one of the most revered photographers of the 20th century, was a master at capturing dramatic, high dynamic range scenes. It's even more incredible that this was done on paper, which has even less dynamic range than computer screens!"

It seems pretty clear to me that in this context the author is referring to the high dynamic range of the scenes that Adams pointed his camera at. That's why he says "captured HDR" and "high dynamic range scenes".

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1. dahart ◴[14 May 25 23:37 UTC] No.43990322[source]▶
> It seems pretty clear to me that in this context the author is referring to the high dynamic range of the scenes that Adams pointed his camera at.

Yes, this is the problem I have with the article. “HDR” is not characterized solely by the range of the scene, and never was. It’s a term of art that refers to an increased range (and resolution) on the capture and storage side, and it’s referring to a workflow that involves/enables deferring exposure until display time. The author’s claim here is making the term “HDR” harder to understand, not easier, and it’s leaving out of the most important conceptual aspects. There are some important parallels between film and digital HDR, and there are some important differences. The differences are what make claiming that nineteenth century photographers were capturing HDR problematic and inaccurate.