sandofsky (u/sandofsky)

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

mrandish · 4 months ago

> That's because this post is about HDR

It's about HDR from the perspective of still photography, in your app, on iOS, in the context of hand-held mobile devices. The post's title ("What Is HDR, Anyway?"), content level and focus would be appropriate in the context of your company's social media feeds for users of your app - which is probably the audience and context it was written for. However in the much broader context of HN, a highly technical community whose interests in imaging are diverse, the article's content level and narrow focus aren't consistent with the headline title. It seems written at a level appropriate for novice users.

If this post was titled "How does Halide handle HDR, anyway?" or even "How should iOS photo apps handle HDR, anyway?" I'd have no objection about the title's promise not matching the content for the HN audience. When I saw the post's headline I thought "Cool! We really need a good technical deep dive into the mess that is HDR - including tech, specs, standards, formats, content acquisition, distribution and display across content types including stills, video clips and cinematic story-telling and diverse viewing contexts from phones to TVs to cinemas to VR." When I started reading and the article only used photos to illustrate concepts best conveyed with color gradient graphs PLUS photos, I started to feel duped by the title.

(Note: I don't use iOS or your app but the photo comparison of the elderly man near the end of the article confused me. From my perspective (video, cinematography and color grading), the "before" photo looks like a raw capture with flat LUT (or no LUT) applied. Yet the text seemed to imply Halide's feature was 'fixing' some problem with the image. Perhaps I'm misunderstanding since I don't know the tool(s) or workflow but I don't see anything wrong with the original image. It's what you want in a flat capture for later grading.)

sandofsky · 4 months ago

> It's about HDR from the perspective of still photography, in your app, on iOS, in the context of hand-held mobile devices.

It's from the perspective of still photography, video, film, desktop computing, decades of research papers, and hundreds of years of analog photography, condensed into something approachable.

> However in the much broader context of HN, a highly technical community whose interests in imaging are diverse, the article's content level and narrow focus aren't consistent with the headline title. It seems written at a level appropriate for novice users.

"On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity"

To be clear, I didn't submit the post, and I never submit my posts. I don't care if my posts make a splash here, and kind of dread when they do because anything involving photography or video attracts the most annoying "well actually" guys on the Internet.

> When I saw the post's headline I thought "Cool! We really need a good technical deep dive into the mess that is HDR - including tech, specs, standards, formats, content acquisition, distribution and display across content types including stills, video clips and cinematic story-telling and diverse viewing contexts from phones to TVs to cinemas to VR."

The post is called, "What is HDR," and the introduction explains the intended audience. That audience is much larger than "people who want to read about ITU-R Recommendation BT.2100." But if you think people are interested in a post like that, by all means write it.

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

mrandish · 4 months ago

> "The first HDR is the "HDR mode" introduced to the iPhone camera in 2010."

Yeah, I had a full halt and process exception on that line too. I guess all the research, technical papers and standards development work done by SMPTE, Kodak, et al in the 1990s and early 2000s just didn't happen? Turns out Apple invented it all in 2010 (pack up those Oscars and Emmys awarded for technical achievement and send'em back boys!)

sandofsky · 4 months ago

This post is written for people who have heard "HDR" and feel confused. That introduction lists two types of HDR people might think about. "The first" means "the first of two types we're going to explain," not "the first research in the chronological history of HDR."

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

dahart · 4 months ago

Hehe outside is “HDR content”? To me that still comes off as confused about what HDR is. I know you aren’t, but that’s what it sounds like. A sunny day has a high dynamic range for sure, but the acronym HDR is a term of art that implies more than that. Your article even explains why.

Tone mapping doesn’t imply HDR. Tone mapping is always present, even in LDR and SDR workflows. The paper you cited explicitly notes the idea is to “extend” Adams’ zone system to very high dynamic range digital images, more than what Adams was working with, by implication.

So how is a “window of luminance values” different from a dynamic range, exactly? Why did you make the incorrect and obviously silly assumption that I was suggesting a camera’s aperture changes the outdoor scene’s dynamic range rather than what I actually said, that it changes the exposure? Your description of what a camera does is functionally identical. I’m kinda baffled as to why you’re arguing this part that we both understand, using hyperbole.

I hope you have a better day tomorrow. Good luck with your app. This convo aside, I am honestly rooting for you.

sandofsky · 4 months ago

> Hehe outside is “HDR content”? To me that still comes off as confused about what HDR is.

"Surprisingly, daytime shots with high dynamic range may also suffer from lack of light."

That's from, "Burst photography for high dynamic range and low-light imaging on mobile cameras," written by some of the most respected researchers in computational photography. It has 342 citations according to ACM.

I'm still waiting for a link to your papers.

> Tone mapping doesn’t imply HDR.

https://en.wikipedia.org/wiki/Tone_mapping

First sentence: "Tone mapping is a technique used in image processing and computer graphics to map one set of colors to another to approximate the appearance of high-dynamic-range (HDR) images in a medium that has a more limited dynamic range."

> Why did you make the incorrect and obviously silly assumption that I was suggesting a camera’s aperture changes the outdoor scene’s dynamic range rather than what I actually said, that it changes the exposure?

Because you keep bumbling details like someone with a surface level understanding. Your replies are irrelevant, outdated, or flat out wrong. It all gives me flashbacks to working under engineers-turned-managers who just can't let go, forcing their irrelevant backgrounds into discussions.

It's cool that you studied late 90s 3D rendering. So did I. It doesn't make you an expert in computational photography. Please stop confusing people with your non-sequiturs.

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

dahart · 4 months ago

Sorry man, you seem really defensive, I didn’t mean to put you on edge. Okay, if you are calling the scenes “HDR” then I’m happy to rescind my critique about Ansel Adams and switch instead to pointing out that “HDR” doesn’t refer to the range of the scene, it refers to the range capability of a digital capture process. I think the point ultimately ends up being the same either way. Hey where is HDR defined as an adjective? Last time I checked, “range” could be a noun, I think… no? You must be right, but FWIW, you used HDR as a noun in your 2nd to last point… oh and in the title of your article too.

Hey it’s great Reinhard was inspired by Adams. I have been too, like a lot of photographers. And I’ve used the Reinhard tone mapper in research papers, I’m quite familiar with it and personally know all three authors of that paper. I’ve even written a paper or maybe two on color spaces with one of them. Anyway, the inspiration doesn’t change the fact that 12 stops isn’t particularly high dynamic range. It’s barely more than SDR. Even the earliest HDR formats had like 20 or 30 stops, in part because the point was to use physical luminance instead of a relative [0..1] range.

8 bit RGB does sort-of in practice describe a dynamic range, as long as the 1 bit difference is approximately the ‘just noticeable difference’ or JND as some researchers call it. This happens to line up with 8 bits being about 8 stops, which is what RGB images have been doing for like 50 years, give or take. While it’s perfectly valid arithmetic to use 8 bits values to represent an arbitrary amount like 200 stops or 0.003 stops, it’d be pretty weird.

Plenty of people have called and continue to call 8 bit images “LDR”, here’s just three of the thousands of uses of “LDR” [1][2][3], and LDR predates usage of SDR by like 15 years maybe? LDR predates sRGB too, I did not actually mean 8 bit sRGB. LDR and SDR are close but not quite the same thing, so feel free to read up on LDR. It’s disappointing you ducked the actual point I was making, which is still there even if you replace LDR with SDR.

What is confusing about the sentence about analog cameras and exposure control? I’m happy to explain it since you didn’t get it. I was referring to how the aperture can be adjusted on an analog camera to make a scene with any dynamic range fit into the ~12 stops of range the film has, or the ~8 stops of range of paper or an old TV. I was just trying to clarify why HDR is an attribute of digital images, and not of scenes.

[1] https://www.easypano.com/showkb_228.html#:~:text=The%20Dynam...

[2] https://www.researchgate.net/figure/shows-digital-photograph...

[3] https://irisldr.github.io/

sandofsky · 4 months ago

You opened this thread arguing that Ansel Adams didn't "use HDR." I linked you to a seminal research paper which argues that he tone mapped HDR content, and goes on to implement a tone mapper based on his approach. This all seems open and shut.

> I’m happy to rescind my critique about Ansel Adams

Great, I'm done.

> and switch instead to pointing out that “HDR” doesn’t refer to the range of the scene

Oh god. Here's the first research paper that popped into my head: https://static.googleusercontent.com/media/hdrplusdata.org/e...

"Surprisingly, daytime shots with high dynamic range may also suffer from lack of light."

"In low light, or in very high dynamic range scenes"

"For high dynamic range scenes we use local tone mapping"

You keep trying to define "HDR" differently than current literature. Not even current— that paper was published in 2016! Hey, maybe HDR meant something different in the 1990s, or maybe it was just ok to use "HDR" as shorthand for when things were less ambiguous. I honestly don't care, and you're only serving to confuse people.

> the aperture can be adjusted on an analog camera to make a scene with any dynamic range fit into the ~12 stops of range the film has, or the ~8 stops of range of paper or an old TV.

You sound nonsensical because you keep using the wrong terms. Going back to your first sentence that made no sense:

> Analog cameras have exposure control and thus can capture any range you want

You keep saying "range" when, from what I can tell, you mean "luminance." Changing a camera's aperture scales the luminance hitting your film or sensor. It does not alter the dynamic range of the scene.

Analog cameras cannot capture any range. By adjusting camera settings or attaching ND filters, you can change the window of luminance values that will fit within the dynamic range of your camera. To say a camera can "capture any range" is like saying, "I can fit that couch through the door, I just have to saw it in half."

> And I’ve used the Reinhard tone mapper in research papers, I’m quite familiar with it and personally know all three authors of that paper. I’ve even written a paper or maybe two on color spaces with one of them.

I'm sorry if correcting you triggers insecurities, but if you're going to make an appeal to authority, please link to your papers instead of hand waving about the people you know.

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

dahart · 4 months ago

I agree capture, format and display are closely related. But HDR capture and processing specifically developed outside of HDR display devices, and use of HDR displays changes how HDR images are used compared to LDR displays.

> The post never said Adams used HDR. I very carefully chose the words

Hey I’m sorry for criticizing, but I honestly feel like you’re being slightly misleading here. The sentence “What if I told you that analog photographers captured HDR as far back as 1857?” is explicitly claiming that analog photographers use “HDR” capture, and the Ansel Adams sentence that follows appears to be merely a specific example of your claim. The result of the juxtaposition is that the article did in fact claim Adams used HDR, even if you didn’t quite intend to.

I think you’re either misunderstanding me a little, or maybe unaware of some of the context of HDR and its development as a term of art in the computer graphics community. Film’s 12 stops is not really “high” range by HDR standards, and a little exposure latitude isn’t where “HDR” came from. The more important part of HDR was the intent to push toward absolute physical units like luminance. That doesn’t just enable deferred exposure, it enables physical and perceptual processing in ways that aren’t possible with film. It enables calibrated integration with CG simulation that isn’t possible with film. And it enables a much wider rage of exposure push/pull than you can do when going from 12 stops to 8. And of course non-destructive digital deferred exposure at display time is quite different from a print exposure.

Perhaps it’s useful to reflect on the fact that HDR has a counterpart called LDR that’s referring to 8 bits/channel RGB. With analog photography, there is no LDR, thus zero reason to invent the notion of a ‘higher’ range. Higher than what? High relative to what? Analog cameras have exposure control and thus can capture any range you want. There is no ‘high’ range in analog photos, there’s just range. HDR was invented to push against and evolve beyond the de-facto digital practices of the 70s-90s, it is not a statement about what range can be captured by a camera.

sandofsky · 4 months ago

> The sentence “What if I told you that analog photographers captured HDR as far back as 1857?” is explicitly claiming that analog photographers use “HDR” capture,

No, it isn't. It's saying they captured HDR scenes.

> The result of the juxtaposition is that the article did in fact claim Adams used HDR

You can't "use" HDR. It's an adjective, not a noun.

> Film’s 12 stops is not really “high” range by HDR standards, and a little exposure latitude isn’t where “HDR” came from.

The Reinhard tone mapper, a benchmark that regularly appears in research papers, specifically cites Ansel Adams as inspiration.

"A classic photographic task is the mapping of the potentially high dynamic range of real world luminances to the low dynamic range of the photographic print."

https://www-old.cs.utah.edu/docs/techreports/2002/pdf/UUCS-0...

> Perhaps it’s useful to reflect on the fact that HDR has a counterpart called LDR that’s referring to 8 bits/channel RGB.

8-bits per channel does not describe dynamic range. If I attach an HLG transfer function on an 8-bit signal, I have HDR. Furthermore, assuming you actually meant 8-bit sRGB, nobody calls that "LDR." It's SDR.

> Analog cameras have exposure control and thus can capture any range you want.

This sentence makes no sense.

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

dahart · 4 months ago

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.

sandofsky · 4 months ago

> It seems like a mistake to lump HDR capture, HDR formats and HDR display together, these are very different things.

These are all related things. When you talk about color, you can be talking about color cameras, color image formats, and color screens, but the concept of color transcends the implementation.

> The claim that Ansel Adams used HDR is super likely to cause confusion, and isn’t particularly accurate.

The post never said Adams used HDR. I very carefully chose the words, "capturing dramatic, high dynamic range scenes."

> 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.

This is just factually wrong. Film negatives have 12-stops of useful dynamic range, while photo paper has 8 stops at best. That gave photographers exposure latitude during the print process.

> 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's a photo of Ansel Adams in the article, dodging and burning a print. How would you describe that if not adjusting the exposure?

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

Diti · 4 months ago

They also make no mention of transfer functions, which is the main mechanism which explains why the images “burn your eyes” – content creators should use HLG (which has relative luminance) and not PQ (which has absolute luminance) when they create HDR content for the web.

sandofsky · 4 months ago

In theory PQ specifies absolute values, but in practice it's treated as relative. Go load some PQ encoded content on an iPhone, adjust your screen brightness, and watch the HDR brightness also change. Beyond the iPhone, it would be ridiculous to render absolute values as-is, given SDR white is supposedly 100-nits; that would be unwatchable in most living rooms.

Bad HDR boils down to poor taste and the failure of platforms to rein it in. You can't fix bad HDR by switching encodings any more than you can fix global warming by switching from Fahrenheit to Celsius.

sandofsky commented on What is HDR, anyway? lux.camera/what-is-hdr/... · Posted by u/_kush

SquareWheel · 4 months ago

FYI: You wrote Chrome 14 in the post, but I believe you meant Android 14.

sandofsky · 4 months ago

Thanks. Updated.