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Generally, the technical image quality of a digital image (before we get to the post-processing stage) is the product of the characteristics of the lens and the recording medium, with an important dash of good technique from the photographer.

Lenses are covered under What characteristics make a good lens good?, but what about the other important component, the sensor? DxOMark famously publishes some measurements, but what's really important? Obviously megapixels are part of it, but what else matters? Are there non-lens camera features other than the sensor which can have a positive or negative effect on image quality?

Most importantly, what do these things look like in actual real-world images, and how can I recognize them by looking it photographs rather than just review charts and graphs?

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+1 great question! Amazing that it was not asked until now. –  Regmi Apr 7 '13 at 16:46
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MOAR MEGAPIXELS! ;) –  Todd Lehman Apr 11 '13 at 22:49
    
Good question! I cannot help thinking that the D800, for example, could offer much better dynamic range and ISO performance if Nikon would pack in less pixels. Say, 24M instead of 35M. Am I thinking wrong here? –  Caetano Sauer Jul 2 '13 at 10:01

1 Answer 1

I'll try to avoid getting too technical - there are others that can fill in more detail. I think, apart from resolution, the most important aspects to me would be dynamic range and low light performance. DxO rates sensors on the following:

Resolution

With sharp lenses and good technique, more pixels can never hurt, especially if you are printing large or cropping wildlife images for example. Apart from those two scenarios, higher resolution is something you usually don't see unless you are pixel peeping, and comparing two similar spec cameras may be hard to distinguish the difference.

Colour Depth

Sensors with more colour depth can resolve more tonal values. I would think that the colour spaces most people use would limit the ability to see real life differences. DxO rates colour depth under the "Portrait" score.

Dynamic Range

I have shot a few frames with a D800, and it's incredible what detail you can pull from both the shadows and highlights compared to older cameras. This is easily seen in real life high-contrast images such as landscapes. In a few years we can ditch HDR, bracketing and throw out our grad ND filters :) DxO rates dynamic range under their "Landscape" score, as extended range is useful to avoid blown out skies.

Low Light (High ISO) performance

This is another measurement that's easy to see in real life examples, as some sensors are certainly better at limiting noise in low light. DxO rates low light performance under their "Sports" score, given its usefulness in poorly lit gyms, stadiums and hocky rinks.

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You left out a critical metric: cost. Except for the D4 and 1Dx, every other camera cares about the cost of the sensor. No matter if it can out-resolve the Hubble, you have to be able to afford it. –  Pat Farrell Mar 17 '13 at 3:01
    
For the purposes of this question, I think it's most appropriate to consider cost as an inherent factor in making any real-world device rather than a "metric". Like power consumption or size, it's something that real designs inevitably balance against rather than an aspect of quality in itself. –  mattdm Apr 1 '13 at 17:58

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