Why do you say that last?
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Photons to photos dynamic range ratings
- Thread starter DavidMillier
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NAwlins Contrarian
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Not sure which you mean about "that last", but two possibilities, starting simple:
(1) "I think!" My point is I'm out of my confidence zone on parts of this. My confidence in my understanding here is modest.
(2) "Except under plenty-of-light circumstances, the effective noise and dynamic range advantage is often less than 0.46-stop, or even nothing ...." What are the limiting factors for any particular shot can get a bit complicated, and somewhat subject to judgment calls about what is or isn't important to capture in any given photo. I consider it borderline-axiomatic that the advantages of a larger sensor or film frame in terms of noise / grain / dynamic range exist only where there's plenty of light relative to the need to stop motion and capture depth of field. But I hesitate to derail the thread, and that sort of statement often seems to generate more heat than light. And of course it doesn't address other advantages that a GFX may have, meaning in some cases higher resolution and possibly a better set of native lenses.
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If you don't need all the dynamic range the camera has, that doesn't reduce the effective dynamic range. It just means the dynamic range of the camera is not important in that situation.
Lens flare could reduce the effective dynamic range or the camera and lens combination.
DavidMillier
Forum Pro
Well done!
And that story reminds me of when I sat an accountancy exam. The year I sat it, they changed the format so there was one massive multi part question at the beginning worth 60% of the marks. It was a complicated question about dissolving and reforming a partnership with new partners. I studied partnerships, of course, and I was sure I could answer the kind of simpler questions they asked in previous exams, but this new approach stumped me. I remember I spent about an hour reading, re-reading and agonising over that question before giving up and concluding I had no way into the question. I did very well on the law and programming papers but failed the whole course horrendously because of that Q1. 40 years later, I still have flashbacks about it and the Royal Horticultural Halls building in Vincent Sq, Westminster where I sat the exam.
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DavidMillier
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I've followed all the responses, and am trying to boil it down to a simplified bulleted list:
GFX100 advantage over a7Riv at 4:3 aspect ratio in good light:
1. Dynamic range and reduced noise. Improvement: c. 0.5 stops. In percentage terms based on the Photons to photos figures that = +4% improvement
2. Max print size enlargeability advantage = 29% [Is the 29% linear or area?]
Have I got these numbers correct?
No. You can’t meaningfully take a ratio of log base 2 values. The improvement is 37.5%.
Linear.
DavidMillier
Forum Pro
I don't understand. Are you saying that a 0.5 stop improvement over 11.67 stops is a 37.5% improvement? Surely that would need a 4.33 stop improvement?
Thanks.
EDIT: These numbers are for the GFX100. I have the 50s. Presumably the print size improvement favours the Sony in this case and the advantage of the 50s is only extra DR and slightly less noise?
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Yes.
It is nonsensical to take the ratio of two logs in this context.
That's like saying that an earthquake of Richter 8 is 33% more than an earthquake of Richter 6.
Uh-huh.
DavidMillier
Forum Pro
Is that what I did? I thought I did 0.5/11.67 stops x100%. = +4%
What's wrong with that?
DavidMillier
Forum Pro
IMO, that's not a legitimate way of looking at it.
Let's go through this slowly.
Let's say we have two linear measurements. One is 100 volts, and the other is 1 volt.
100 volts is 9900% greater than 1 volt.
Now let's take the log base 10 of both.
Now we have two numbers: 0 and 2.
It would be nonsensical to say that the larger of the two logs was infinity percent more than the smaller one.
DavidMillier
Forum Pro
I'm not following this talk of log this and log that, sorry.
But you've made me think this through a bit. What I think you must be saying is that a 1 stop increase = x2 so a half stop increase is...er... sqRt(2) or +40%.
Something like that, maybe?
From Wikipedia:
In mathematics, the logarithm is the inverse function to exponentiation. That means that the logarithm of a number x to the base b is the exponent to which b must be raised to produce x. For example, since 1000 = 10^3, the logarithm base 10 of 1000 is 3, or log10 (1000) = 3. The logarithm of x to base b is denoted as logb (x), or without parentheses, logb x.
The logarithm base 10 is called the decimal or common logarithm and is commonly used in science and engineering. The natural logarithm has the number e ≈ 2.718 as its base; its use is widespread in mathematics and physics, because of its very simple derivative. The binary logarithm uses base 2 and is frequently used in computer science.
Logarithms were introduced by John Napier in 1614 as a means of simplifying calculations.[1] They were rapidly adopted by navigators, scientists, engineers, surveyors, and others to perform high-accuracy computations more easily. Using logarithm tables, tedious multi-digit multiplication steps can be replaced by table look-ups and simpler addition. This is possible because the logarithm of a product is the sum of the logarithms of the factors:
provided that b, x and y are all positive and b ≠ 1. The slide rule, also based on logarithms, allows quick calculations without tables, but at lower precision. The present-day notion of logarithms comes from Leonhard Euler, who connected them to the exponential function in the 18th century, and who also introduced the letter e as the base of natural logarithms.[2]
Yes.
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DavidMillier
Forum Pro
I was hoping to never have to wade through explanations of that sort againFrom Wikipedia:
In mathematics, the logarithm is the inverse function to exponentiation. That means that the logarithm of a number x to the base b is the exponent to which b must be raised to produce x. For example, since 1000 = 10^3, the logarithm base 10 of 1000 is 3, or log10 (1000) = 3. The logarithm of x to base b is denoted as logb (x), or without parentheses, logb x.
The logarithm base 10 is called the decimal or common logarithm and is commonly used in science and engineering. The natural logarithm has the number e ≈ 2.718 as its base; its use is widespread in mathematics and physics, because of its very simple derivative. The binary logarithm uses base 2 and is frequently used in computer science.
Logarithms were introduced by John Napier in 1614 as a means of simplifying calculations.[1] They were rapidly adopted by navigators, scientists, engineers, surveyors, and others to perform high-accuracy computations more easily. Using logarithm tables, tedious multi-digit multiplication steps can be replaced by table look-ups and simpler addition. This is possible because the logarithm of a product is the sum of the logarithms of the factors:
provided that b, x and y are all positive and b ≠ 1. The slide rule, also based on logarithms, allows quick calculations without tables, but at lower precision. The present-day notion of logarithms comes from Leonhard Euler, who connected them to the exponential function in the 18th century, and who also introduced the letter e as the base of natural logarithms.[2]
Then again I am reading Greg Egan's Disapora novel and every page looks like the above....
There is an interesting thing going on here. Metrics like stops are designed to make it easy to compare quantities in photography by bypassing the technicalities. And it works. But, after a while, it just becomes numbers you use unthinkingly without a feel for what it means in absolute terms. +1 stop doesn't sound very much, does it, if you just let it roll off the tongue. But it is actually quite a big step change. It's easy to get blase and forget that. Unless you are an engineer, of course. Glad you put me right.
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NAwlins Contrarian
Forum Pro
In my opinion, this whole discussion (the several responses below the message to which I'm replying) doesn't have so much a 'correct side' and an 'incorrect side', as it has a lack of clarity regarding what are the appropriate numbers with which to compare. With light--and sound, to give another common example--human perception is more logarithmic than it is like linear / absolute. Increasing the absolute, measurable, linear quantity of light by 2x = +100% = +1 EV = +1 stop only increases the human-perceived brightness to a modest (albeit clearly-visible) degree. With sound pressure levels, to seem twice as loud requires about a 10 dB increase in SPL, which is ten times a high in a more absolute / linear sense.
When discussing camera performance, do we want to talk in more absolute / linear units, or in more human-perceptual / logarithmic units? I don't think either is the clearly-better approach for all uses. IMO both can be helpful ways to think of things, in the right contexts.
So as a matter of measurement in usual scientific terms, I totally understand the view than a one-stop improvement in 100%, a half-stop improvement is 41%, etc. And I do see some difficulties that can arise from e.g. a claim that a camera that can capture 11 stops of dynamic range has 10% better / more dynamic range than a camera that can capture 10 stops of dynamic range. But I don't think such a claim of 10% improvement is wrong or misleading or unhelpful or inappropriate.
But all that's just my personal opinion!
[ETA]
Part of the problem may be that for light we don't seem to have a term that's clearly as based on human perception as "loudness" is for sound.
(And part of the problem is that a lot of guys think their 100 Watt-per-channel amp should be twice as loud as a 50 Watt-per-channel amp, clueless about the fact that to be twice as loud they'd need a 500 Watt-per-channel amp. Guys with cameras suffer similarly.)
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I've been working with light a long time, and a one stop increase seems like twice as much light to me.
For me, twice as loud is a 6 db increase, or twice the voltage. I have been working with audio for a long time, and that may influence my perception. Years and years of experimentation die hard.
If we wanted to talk in perceptual units, why not use L*?
It leads to, IMHO stupid, things like this:
The difference between 1 stop and 2 stops is 100%.
The difference between 0 stop and 1 stops is infinite.
The difference between 10 stops and 11 stops is 10%.
Another reason to not use perceptual measurements for things like dynamic range is that they ignore the effect of postproduction. If you've got a scene with 12 or 13 stops of DR and a camera capable of capturing that, you're not going to see that many stops of DR in the final print. The DR of the scene will be mapped into the DR of the print medium (Dmax 2.5 or less, which is 7 or 8 stops), with the highlights being suppressed and the shadows being boosted.
Greg7579
Forum Pro
I knew when you started this what was going to happen. Of course you don't understand it and you never will. That is not slight. Just a fact. True for me too. Mostly.
Look, David, I think GFX (even 50) has better image fidelity than any FF because I know it and see it every day.
You have the very fine alphasevenarefour and the GFX 50 something. Go shoot both and decide what you like. There is room for both systems. Tools for the job.
No need to try to figure out the math and try to establish in your mind a percentage difference.
That's not your bag. Leave that to the guys who like to talk about that stuff.
You are digging a hole you will never get out of.
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