i feel like people always downplay megapixels

Started May 1, 2012 | Discussions thread
PaulRivers
Senior MemberPosts: 7,414
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Re: Pixel count vs resolved detail
In reply to Great Bustard, May 1, 2012

Great Bustard wrote:

And that's why it's downplayed. Because ever since 5-6mp cameras, it's been diminishing returns in the amount of real detail seen. In the 10-16mp camera category, some cameras with more megapixels actually produce less detail than cameras with more megapixels (that that I said some, not all).

This is not true. For any given lens, sensor size, and relative AA filter strength, more pixels will always resolve more detail.

It is true that it's been diminishing returns.

For the second part, I disagree strongly, I've seen a few comparisons where the camera with lower megapixels resolves more real detail than the camera with more megapixels.

However, to be clear, I specifically said "some", aka, "a rare few".

There is debate on whether that's a sensor issue (megapixels), or whether the higher mp camera just has a worse lens, worse, design, etc etc. But the OP's original post was on "downplaying" the megapixel rating, and this is why the megapixel rating is downplayed - because there's no huge difference between today's cameras with different megapixel ratings once they got into the 10-16mp range (with the same size sensor).

I suppose I should add that I'm thinking of compact cameras. To be fair, writing this I realized others might be thinking of dslr's, and the point of not gaining advantage is different with a larger sensor and a sharp lens.

But even when they do produce more detail...

...which is usually...

...it's by a very, very, very tiny amount.

Consider the Canon 50 / 1.4 at 8 MP:

http://www.photozone.de/canon-eos/159-canon-ef-50mm-f14-usm-test-report--review?start=1

and 15 MP:

http://www.photozone.de/canon-eos/565-canon50f14apsc?start=1

Under ideal conditions, it can resolve 26% more across the frame.

I don't know how to read those charts, my thoughts are based on studio comparison shots, and would bring up the issue of how fair the test is (there's a lot of debate about whether dx0 mark results are actually indicative of real world results).

To be fair, I wasn't thinking of dslr's when I wrote my post (which in retrospect is a category that isn't excluded from this thread).

Look at the studio comparison shots here at dpreview or at imaging resource. A new camera comes out with more megapixels, and it's often nearly impossible to tell the difference in side-by-side, 100% crop, direct comparison, studio controlled images. If there is a difference, there's someone claiming "huge, dramatic differences!" when they're like "if you look at this specific part of the image, you can 'clearly' see that some of the lines are very slightly sharper on the new model vs the old model".

Of course, comparing photos made from different numbers of pixels at 100% isn't the best way about it. One would upsample the lower pixel count photo (ideally, without interpolation) to the size of the larger pixel count photo, and then compare.

That's a side topic, my point was that whether you resize them or not it's the same deal - differences are measured in terms like "at 100%, camera b has slightly more defined lines than camera A!" and then is claimed to be some sort of huge difference.

The difference is usually (though not always) there, but at this point it's nearly always tiny.

Now some people have gone to far the other way, claiming that more megapixels is some kind of negative (which it usually isn't), but downplaying the megapixel count is accurate - it just doesn't make much of a difference. And I don't mean in some silly "you don't need more detail" sort of way - we'd all love more detail. I mean in a "you don't actually get more detail" kind of way.

Many factors limit how much detail can be squeezed out of the photo:

  • lens aberrations

  • diffraction

  • DOF

  • motion blur

  • camera shake

  • AA filter

  • jpg engine / RAW processor

  • involuntary NR (noise reduction)

  • noise

So, while more pixels will always resolve more detail (for a given lens, sensor size, and relative AA filter), how much more detail you get from those extra pixels is another matter entirely.

And my point is that the returns from modern cameras nowadays from more megapixels are usually so small that those other factors make a much larger difference than the differences in megapixel counts between modern cameras.

For example, even in dslr's, the Nikon d800 is 36.3mp. The Canon 5d Mark 3 is 22.3mp. The Nikon has 62.8% more megapixels than the Canon does....

But even the most optimistic reviews of the d800 suggest it only has a fraction more detail than the Canon. And to get that, you have to blow up the Canon shot to the Nikon size and view it at 100%.

The OP said that megapixels are "downplayed" - I think that they are, and rightly should be. That's different than saying "they don't matter at all".

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