Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
OP Great Bustard Forum Pro • Posts: 40,355
Re: Hilarious!

FrankyM wrote:

You are assuming that read noise scales with pixel area.

I am not "assuming" -- I am defining "equally efficient sensors" as two sensors with the same QE, same read noise / area, and same saturation limit / area.

Yes, you are defining a situation designed to give you the answer you want.

What is the "answer that I want", and what's my agenda for wanting that answer? That smaller pixels, for equally efficient sensors, always result in greater IQ?

The answer you want is one that demonstrates smaller pixels have higher IQ than larger ones.

It's not an answer I "want" -- it's an observation that fits the facts, and those facts are that more pixels on a sensor of a given size result in a photo with higher IQ, if the sensors are equally efficient (same QE, same read noise / area, same saturation limit / area).

In fact, for many non-trivial measures of IQ, more pixels results in greater IQ even if the sensor with more and smaller pixels isn't as efficient.

Your example boils down to a question of read noise, as I said before, so consequently the choice of values determines the outcome. So in effect, you are defining the result.

No -- my example demonstrated how smaller pixels (for a given sensor size) result in less noise if the sensors are equally efficient.

That said, read noise is only an important player in the shadows of a photo, which is why it plays such an important role in DR. However, the dominant source of noise in most photos is photon noise, which is determined by the amount of light falling on the sensor and the QE. In that context, QE is the more important player, by far, than read noise for most photography, and pixel size plays no role in QE.

So, for example, the reason the Nikon D3s whomps all over the Canon 5D2 in terms of noise performance is because it sports a 57% QE vs the 5D2's 33% QE. On the other hand, the importance of more pixels cannot be overlooked, since that extra detail can be sacrificed for lower noise via NR (noise reduction):


But if you really want to make a comparison between large and small pixels you should start with a level playing field. Read noise, for a given manufacturing process, simply does not scale with pixel area. Therefore, your definition is comparing apple with oranges.

What is this "level playing field"? Here -- you may find this discussion relevant:


No, I don't because I'm not arguing whether larger of smaller pixels have more IQ.

OK, I'm listening.

I'm saying that if we compare two hypothetical sensors whose only difference is the pixel size and that are manufactured with the same process generation, the read noise of one does not scale to the other by pixel size. If we use different manufacturing process generations then I think it's not a proper comparison.

Did I ever say, or imply, otherwise? I did, however, give the example of the 5D2 and E5 sensors, where they are so close to the same efficiency as I've defined "efficiency", that it is almost as if Olympus just scaled down the 5D2 sensor (of course, I'm not saying that's what they did -- I'm just giving those sensors as an example of the fact that two sensors with the same, or nearly the same, efficiency isn't as rare as people make it out to be).

Sorry, I hadn't seen the above post. But it doesn't really answer my question.

What was your question? How read noise varies with pixel size in the real world? Depends on the specific cameras being compared:


No. If you give me an example where you express read noise/area then I ask what the physics is of read noise varying with pixel area. However, since you now clarify that you were defining a hypothetical sensor whose read noise was exactly 4 times the other sensor of your example, my question is irrelevant.

OK, sure. Anyway, let's recap:

  • Sensors that are "equally efficient" have the same QE, same read noise / area, and same saturation limit / area.

  • If sensors are equally efficient, then for sensors of the same size, more pixels (smaller pixels) results in photos with greater IQ.

  • The overall trend is towards sensors with smaller pixels and greater overall efficiency.

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