Return of Interesting article on DxO about 5D III and D800...

Started Apr 10, 2013 | Discussions thread
qianp2k
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Re: Return of Interesting article on DxO about 5D III and D800...
In reply to aftab, Apr 11, 2013

Very interesting to read and excellent writing

http://www.dxomark.com/index.php/Publications/DxOMark-Reviews/Looking-for-new-photo-gear-DxOMark-s-Perceptual-Megapixel-can-help-you

DXOMark indeed uses words sharpness and resolution interchangeably as you can see in its above explanation of Perceptual Megapixel. It uses the word "sharpness" but then it explains the reasons to change to P-MPix unit,

This measurement bypasses the problems inherent to MTF:

  • Describes resolution with a single number,
  • Correlates with the way the human vision perceives resolution
  • Uses a unit that is well-known to photographers — the megapixel.

Anyway DXOMark's sharpness is not regular sharpness you can enhance in software but a resolution that human eyes can perceive - perceptural sharpness expressed in MP unit.

aftab wrote:

Strictly speaking, this is not a reply to your OP only, it is more like a response to everything posted so far.

I see lots of accusations here, people don't understand the terms resolution and sharpness clearly etc. And to support this assumption there are lots of articles in the web too. Funny, really!

Scenario A

One doesn't need to be a rocket scientist to know that A is sharper than B. We often get lost in definitions and numbers and frequencies etc. But one can easily see sharpness. In this case it is about more contrast and more well defined edges (abrupt and clear transition of information from black to white or Actuance). So, if we really insist on defining sharpness we can say Sharpness = Clarity.

How about resolution?

Scenario B

Does anyone really think that some people don't know that A has more resolution than B? Yeah, it shows so many line pairs/so much area.. yaada yaada and one can talk about how Fourier transform or that nyquist frequency can explain them. But everybody knows what they see, Resolution = Detail.

Now, we must talk about real world, because that is the norm in this forum (as if we can ever capture something that doesn't belong to this world:P).

Scenario C

A has more resolution than B, because we can count 1753 hair in A vs 1248 hair in B.

Now, let us look at scenario B and scenario C again. In both cases A looks sharper than B. What does that mean? More resolution = more sharpness. That is resolution = sharpness in this two scenarios. And almost all scenarios are like this. So, we can actually use the terms resolution and sharpness interchangeably.

At this point if you have this intense desire to shout at me and say, you don't understand nothing, please look at at scenario A again. We all understand sharpness when we see it. But some of us will hang on to the definitions forever and will deny that fact that sharpness (sharper edge transition) and resolution (detail) are the same for all practical purposes (display size, viewing distance, visual acuity etc). When you have better details in an image it is because the edges of those details are clearly defined. The portrait that shows more hair and skin pores will appears sharper than the one that shows less hair and no skin pores.

Things get a bit complicated if we try to understand how pixel count of a sensor translates into image resolution and as such image sharpness. But we know that law of diminishing return works here and better lens with higher actuance capability combined with higher MP sensor will give the sharper perceptible image than lesser lens with same sensor.

Anyways, another picture

We can say A has higher resolution. Or we can say A is sharper. Same thing.

Disclaimer: I may change my mind tomorrow morning, I am drinking wine at the moment. Australian Penfolds red wines are really nice.

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