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Comment by marricks | Hacker News Reader

I love how, if you do view it accurately, it just makes every other white look washed out and grey in comparison. Our visual system is just one big comparison machine.

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It's really striking if you have a projector. Before you turn on a projector in a room that isn't dark, a white wall looks pretty white. Once the projector is on, that "pretty white" wall is now playing the role of black in the projected scene.

That's almost so obvious that I never thought of that :D

And the color brown doesn't exist on its own. It's orange with context.

HDR content also seems to force the "regular" white to be less bright on an iPad with a regular SDR IPS display.

This is actually super interesting: for displays that can get bright enough for HDR content, but do not have self-illuminated pixels/local dimming zones/any other mechanism to display very dark content alongside very bright (like, say, most modern iPad and Mac screens), this is exactly what is happening.

macOS/iPadOS cranks the backlight brightness up but then adds a black filter to the non-bright content to sim it back to “normal” levels.

https://prolost.com/blog/edr

Yeah, it seems to auto-dim the "SDR" brightness range a bit too much; the jump in the white background brightness ends up being clearly noticeable when e.g. I'm switching to an from the superbright QR code tab in the browser

Outside sunlight is 1000x brighter than inside light

I'm reminded of this every summer when I go indoors or outdoors.

Next time you see a scene in a movie where people enter a house and you can see both the interior and exterior, think about the 1000x ratio and how much artificial light was needed inside the house to balance the lighting in the shot. (Assuming it's a real sunlit exterior and not a sound stage, of course.)

Cinema cameras also have >14 stops of dynamic range that can be extracted in post.

It's been a while since I was on a set, but most DPs seemed to adhere to the principle: "When in doubt, add bigger lights."

In the modern digital era, that has actually changed quite a bit. Now cameras are really sensitive – the equivalent of what used to be 2500 to 4000 ISO is now really common – so instead of adding light, often you have to flag off light in areas you want dark.

So instead of many bright lights you just have duvetyne and flags everywhere, which many DoPs have complained is harder to work with.

Can someone ELI5 this "stops" concept for DR? It is similar to a number of bits that can represent more or less precise information?

A stop is double the amount of light. Useful for equivalence across different ways of changing exposure. So I halve my shutter speed I’ve lost a stop. But I increase my aperture from 4 to 2.8 I’ve gained that stop back. Or I double the sensitivity of my film or sensor (eg. iso 400 to 800).

So yes, in terms of data if using linear gamma exactly equivalent to bits. This is why log gamma curves are used to store for eg 16 stops of light info in 12 bit format

Imagine light represented as a floating point number of the type a * 2 ^ b

Stops describes the range of the exponent b.

With a typical cinema camera, max_b > min_b + 14

You can use tricks like gradient ND filters to increase the perceived range within of a frame or variable NDs to slowly adjust over time (like our eyes do)

Your 5 year olds are very good at maths

Or ND the windows. Or shot on a modern cinema camera, tbh. 1000x is what, ~10 stops? Arri claims 17 for the new 35, though I’ve not had a play

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