Megapixel Recap

January 20, 2010

I woke this morning to discover that my post about megapixel madness was up to 344 comments on the Reddit “technology” page, as well as generating a lot of talk at The Consumerist. It seems to have struck a nerve.

There’s nothing like having 20,000 people suddenly read your words to make you panic, “could I have explained that a little better?” Let me say a couple of things more clearly:

  • Yes, some people DO need more megapixels

Anyone who makes unusually large prints, or who routinely crops out small areas of the frame, does benefit from higher megapixel counts. However, those pixels are only useful if they can add sharp, noise-free information.

The typical point & shoot CCD would fit on top of a pencil eraser. There are fundamental limits on how much detail you can wring out of them. So, the giant-print-making, ruthlessly-cropping photographer really needs to shop for an “enthusiast” camera model—one with a larger sensor chip.

  • Diffraction sets theoretical limits on image detail

Many more people viewed the “Swindle” post than read my explanation of diffraction. The key point is that even if you have a lens that is well-designed and flawless, light waves will not focus to a perfect point. The small, blurred “Airy disks” set a theoretical limit on how much actual detail a lens can resolve.

Up to a point, “oversampling” a blurry image with denser pixel spacing can be useful. But today’s point & shoots have clearly crossed the line where the pixels are MUCH smaller than the Airy disk, and squeezing in more pixels accomplishes nothing.

Plus, making pixels tinier actually worsens image quality in other respects. Marketing compact cameras by boasting higher megapixel counts is simply dishonest.

  • Higher-quality lenses can’t fix this

Better lenses are preferable to bad ones; but diffraction puts a ceiling on what even the best lens can do (yes, even one with a German brand-name on it).

To get greater true image detail, the entire camera must scale up in size. This makes the Airy disks a smaller fraction of the sensor dimensions.

  • Tiny pixels are low-quality pixels

A pixel that intercepts less light is handicapped from the start. Its weaker signal is closer to the noise floor of the read-out electronics. There’s more random brightness variations between adjacent pixels. Each pixel reaches saturation more quickly—blowing out the highlights to a featureless white.

I’m aware of the theory that higher-resolving but noisier pixels are okay, because in any real-world output, several pixels get blended together. But I’ve seen enough photos with weird “grit” in what ought to be clean blue skies to be suspicious of this.

First, random pixel fluctuations interact in strange ways with the color demosaicing algorithm. Distracting color speckles and rainbowing seem apparent at scales much larger than the individual pixels.

Second, the camera’s noise-reduction algorithm can add its own unnatural artifacts—obscuring true detail with weird daubs of waxy color. (This was the problem highlighted in my example photo.) It’s better to have less noise from the start.

  • Many compacts perform much better than this one

That’s true. But isn’t reading an exaggerated polemic much more fun?

Let me be clear that my complaint is about TINY CHIP point & shoots. The new micro Four Thirds cameras (which I am following closely) were created specifically to address the shortcomings of small-sensor cameras, while remaining pocketable. But they cost a lot, at least so far.

Mainly, my complaint is about honesty. Camera makers are slapping big “14 megapixel” stickers onto cameras with tiny chips.

I just want people to understand that—as The Consumerist headlined it—these are “Marketing Lies.”


21 Responses to “Megapixel Recap”

  1. reasonluvr Says:

    That image also displays JPG compression artifacts. How can we be sure that the artifacts you describe are not functions of the lossy compression?

    • petavoxel Says:

      You’re right that I don’t know what JPEG quality setting was used here. But the nature of JPEG artifacts that I’ve seen are mostly “sparklies” around high-contrast edges; JPEG does pretty well with smooth color areas.

      In my example, the main defect is the paint-like blobs of solid color. Look at the details in the water surface. To me that looks more like a camera noise-reduction artifact.

  2. Alex Cummins Says:

    I got on the digital wagon early back at 640×400 but when they reached 2 megapixel (my trusty nikon 950) We were there. I was still fighting film people but I had a 16×20 print of a 2 megapixel image (well taken)that a pro lab made for me and you cant see pixelation except in a couple spots and you have to look for it. As most CONSUMERS only rarely make 8 x 10’s I always point and say pixels no longer matter. Crop in camera and expose properly and vitually any consumer pixel numer will do. You are 100 percent right about the pixel rip off. It is designed to get people to dispose of perfectly good cameras and upgrade. POINTLESS as well over 95% of the photos are never printed greater than 4×6 and and probably 85% of those are never even printed. Thanks for fighting and the work

  3. Darin Says:

    So I have a Nikon D40 (6 MP) that I am happy with. I recently got a panasonic P&S that also takes video for something to have in the pocket, video, etc. This P&S is 10 MP. I totally get that the sensor is small and the pixels are high, and so the pixels are very small. If I turn the setting down to 7MP or 5MP, will I see any improvement?

    • petavoxel Says:

      This seems to be the most-asked question I’m noticing in the various comment threads.

      My answer is that it probably does not reduce real detail (check that out yourself, using the camera’s various res options); and you will save on file size.

      The answer is less clear about noise. When you look at a photo unmagnified on a computer screen, or make a normal-sized print, many individual noisy pixels get blended together. Doing that beforehand with the camera’s own processor won’t necessarily give any advantage. But it’s probably best to try it with your own camera and see if the image seems less speckle-y with the lower res settings. Blue skies in photos are a good place to look for noise.

  4. wouter Says:

    I totally agree with you, that 12MP in a tiny camera is ridicules.
    But which camera is there which you would recommend, with less then 7MP to buy?

    Al recent camera’s have 10MP or more …
    No recent 7MP.

    • petavoxel Says:

      Unfortunately, you’re right—cameramakers have dropped all the compact models with a reasonable pixel count.

      If you demand a pocket-sized camera, and don’t want to risk buying an older model off eBay, one ray of hope might come from Canon. Their recent S90 model actually backed off slightly on the megapixel race. I still think 23 Mp/sq. cm is too high, but it’s an improvement.

      But that’s quite an expensive, “enthusiast” model. Where are the affordable models with that same pixel density?

  5. petavoxel Says:

    By the way, let me be clear that numerous other writers about photography and technology have mocked the “megapixel arms race,” long before me.

    David Pogue started railing about this subject in the New York Times more than three years ago

  6. donjumpsuit Says:

    I absolutely agree with your assessment.
    In addition, I would like to point out that most point and shoots are purchased for convenience, meaning you want to enjoy the ability to take pictures but don’t want to compromise that with having to lug around a camera bag. Usually this comes into play at night when enjoying friends at bars, parties, concerts, and clubs. This is where the point in shoot absolutely fails, in low light situations, and with an inadequate flash that is too close to the lens.

    The last point and shoot I purchases (Sony T1) I ended up giving away with no replacement planned. I love taking pictures (a search of flickr with my username will reveal this passion), but figured at this point my 3MP iPhone camera is just as bad as any point and shoot and can be substituted one-for-one.

    I am currently hoping to join the movement back to a traditional DSLR, although more expensive, impossible to carry discretely at night, and always must be concerned with its safety due to theft, if you love photography, you must make sacrifices. In this case the sacrifice is convenience, not quality. I am glad that the current DSLR’s have incorporated movie mode abilities, which traditional purists scoff at, but is very important in keeping such a hefty piece of hardware versatile, helping the decision to keep it handy during daily life.

    Low light capture is so ridiculously important, something where point and shoot cameras absolutely fail. Startling people with a flash takes all the intimacy and surprise out of capturing life as it exists in real time.

    • petavoxel Says:

      I’m an available-light shooter myself, which is one reason the terrible noise performance of most compacts annoys me so much.

      It’s exciting there is a huge amount of buzz recently about “big sensor small camera” alternatives, like the Panasonic GF1 and Olympus E-P1. But this hasn’t filtered back down to the affordable, consumer end of the market.

      It’s time.

  7. jdpafundi Says:

    This is a truly well written article. Even with all the technical terms strewn about, it was very easy to understand. It really is amazing what these camera manufacturers have people believing nowadays; the world is completely caught up in megapixels. It’s funny because I just picked up a Nikon D90 because I’m getting serious about photography and my Canon P&S really has it’s creative limits. Anyway, when I took it to my parent’s house for the first time, the first question my brother asked me was, “Woah, how many megapixels does it have?” I answered that it has 12 and he was completely blown away like it was the greatest thing on the planet. I had to laugh because it just was a perfect example of how our society has been manipulated by the race to higher megapixel counts.

  8. Ranger 9 Says:

    I’ve enjoyed this series, although I feel that one of the most important points was a bit buried: who needs all those extra pixels anyway?

    The ways most of us view our images (HDTVs, computer monitors, reasonable-size prints) don’t need anywhere near 14 megapixels for maximum-quality reproduction. I wrote a post of my own about this last year:

    Pinching pixels at the expense of image quality is bad enough, but pinching pixels that are going to BE THROWN AWAY ANYWAY is ridiculous. I don’t feel that “fraud” was too strong a word for this scam!

  9. Matt Needham Says:

    If people took the time to do some test shots instead of trying to write refutations to your article they could see what you’re saying with their own eyes. With my 10mp Canon G7 it’s easy to see the effects of aperture diffraction at apertures of f/4.5 and smaller. In my opinion it’s usable aperture range is f/2.8 to f/4. Great articles!

  10. emptyspaces Says:

    A well-written explanation. I’ve been sick to death of all this megapixel nonsense for a long time, too. Keep on fighting the good fight!

  11. Kai Says:

    Here’s a question I don’t think I’ve seen yet. Unless I read incorrectly, you are referring to Point and Shoot cameras. How about DSLR cameras… does the same principle apply?

    (Sorry if this question was already mentioned and I missed it.)

    • petavoxel Says:

      Yes, this is the same reason “full frame” DSLRs will always have an advantage over APS-C models.

      Lets put it this way: Nikon just introduced their new top-of-the-line D3s—their flagship model for photojournalists and sports shooters. It costs over $5000. Presumably they could afford whatever kind of technology might make the images come out better.

      But it’s just a 12 megapixel camera. Considering the sensor dimensions, that’s shockingly low. However that makes each pixel freaking huge (relatively speaking). Even shooting in extremely dim light, the camera can take pictures with very little noise.

      I just added a new post with a comparison of different pixel sizes, which goes into this further.

  12. douginator Says:

    Stay after this. More people need to know about this information!

  13. […] of megapixels in a camera is just salesmanship and gains no actual benefit. The author later gives more explanation of his argument, which is that diffraction puts a physical limit on the useful size of a pixel for […]

  14. James Says:

    So if all the experts/photo enthusiasts now agree why not pressure the camera companies? I as an “averge Joe” read the camera review sites/forums to help me pick a camera/improve my knowledge/photo skills. I’m sure that if the focus was put on the feature that matter eg size/quality of sensor chip, lens, etc) that companies would start to shy away from using megapixels as the selling point.

    After all how do you think the average person got to know of “megapixels” in the first place – It was from the “experts” telling them to use that as the guide in selecting cameras! Lets hope this is the start of a change in thinking/selling digital cameras.

    PS. Surely it’s not that much harder to make a bigger/better/cheaper sensor chip these days?!

  15. […] all. I did try to respond to many of the questions and misunderstandings that I was seeing, in a followup post here. And I’ve expanded on the same issues in many other posts as […]

  16. jednoucelovy Says:

    Some time ago I attended a lecture on new approaches in optical sensors research. The lecturer pointed out an interesting (and little known) fact that the human eye sees more details than what would correspond to the density of the photosensitive cells. The neural processing in retina exploits those diffraction “airy disks” (covering several cells) to actually bring up the effective resolution rather than suffering from diffraction blur. As far as I know, contemporary consumer cameras are nowhere near adopting any kind of diffraction super-resolution.

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