Games Look Bad: HDR and Tone Mapping

Re:Games Look Bad: HDR and Tone Mapping by zokier on Monday October 23, 2017 @05:33PM (#15537113)

I'll try to explain it the way I understand it, which might be completely wrong.

Imagine you have a lightbulb (producing let's say max 1000 units of light/brightness [which are two subtly different things]) connected to a dimmer that has for example 8 discrete levels. What would you say the dynamic range of this setup would be? Obviously measuring the contrast ratio from when the dimmer is in the zero setting (=light off) to max setting would result infinite contrast ratio/dynamic range. That is not very useful though, so the next best thing is to measure brightness difference from the lowest on setting ("1") to max, which gives you actually a reasonable number, in this scenario 125:1000 or 1:8. I hope this example was illuminating.

So I guess the idea is that bit depth fundamentally determines what is the minimum brightness representable without going to zero (where be dragons), and as such determines the max usable dynamic range.

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Re:Games Look Bad: HDR and Tone Mapping by chrisseaton on Monday October 23, 2017 @05:49PM (#15537211)

That still doesn't make any sense.

You could have a dimmer that goes from one level of lightness, up to another, with 8 steps in between. And you could have another dimmer that goes between exactly the same two levels of lightness. The same range. but with 1,000,000 steps in between. The range of the two dimmer switches is the same. They both go from the same minimum to the same maximum. Just the number of steps in between is different. The number of bits represents the number of steps.

Why is 1,000,000 steps the required number? 1,000,000 is just the number of integral factors in the range in base 10. But why is an integral factor more important than a fractional one? They could both be perceptible to a human. The range is the same in both cases, and the given explanation was given that the range was so high.

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Re:Games Look Bad: HDR and Tone Mapping by zokier on Tuesday October 24, 2017 @02:49AM (#15539717)

> And you could have another dimmer that goes between exactly the same two levels of lightness. The same range. but with 1,000,000 steps in between. The range of the two dimmer switches is the same. They both go from the same minimum to the same maximum.

The thing is that you can't set the minimum value arbitrarily, because the scale is anchored to zero. So "1" is always one step above zero, and the step size is a function of bit depth.

So going with our example here, a dimmer with 1000000 steps would not have the same range as dimmer with 8 steps, because the the minimum brightness of one is 1/1000000th of max, and 1/8th of the max for the other (assuming linear scale for simplicity's sake, the principle applies to nonlinear scales too)

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Re:Games Look Bad: HDR and Tone Mapping by zokier on Monday October 23, 2017 @05:42PM (#15537172)

I suppose more engineery explanation would be that we allocate "0" to represent everything below noise floor and whatever maximum value to represent saturation, which leaves us with [1,max-1] as the useful range for our signal. And the dynamic range is in respect to that, instead of [0,max]

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Re:Games Look Bad: HDR and Tone Mapping by chrisseaton on Monday October 23, 2017 @05:52PM (#15537235)

Another way to explain it is that for every two dimmer settings you can create, there is another luminance value between those two settings that you could have as an additional setting if you wanted. When do you stop adding new settings? Why stop when you have a million settings? Why is that a magic number?

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Re:Games Look Bad: HDR and Tone Mapping by pault on Tuesday October 24, 2017 @10:22AM (#15541724)

At a certain point you'll hit the physical quantization of light, so that may be where the number comes from.

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