How Big Are My Pixels?

January 21, 2010

In the firestorm of comments about the Great Megapixel Swindle,  a couple of questions kept coming up: “Instead of megapixels, what should I be looking at? And how do I even know what chip size a camera has?”

Well, cameramakers designate chip sizes using an almost incomprehensible naming system (inherited from video tubes, if you really must know) using numbers like 1/2.3″. In fact, if we don our conspiracy tinfoil hats, it’s almost as if they’re deliberately making it hard to understand the true size.

Thankfully there’s a table decoding various sensor formats here. (Though that page has grown a little dated: There are no longer any 2/3″-sensor models on the market, sadly.)

But the number I really care about is, what is the size of the pixels? Yes, new technology might still come up with a few sensitivity-enhancing tweaks. But loosely speaking, the bigger each pixel is, the better.

Pixel width is quoted in microns—sometimes abbreviated µm or um. But it’s not often listed directly in camera specs.

But many in-depth review sites like DPRreview will give the “pixel density” in their model listings. Note the ridiculous jump from the consumer point & shoots (between 35 and 50 megapixels per square centimeter) versus the serious DSLRs (1.4 to 3.3).

Might this tell us something?

So as a handy conversion reference, here’s how to translate some of those density numbers into actual pixel sizes*

  • 50 Mp/sq. cm —> 1.4 micron pixels

[e.g. 14-megapixel compacts]

  • 35 Mp/sq. cm —> 1.7 micron pixels

[10-megapixel compacts]

  • 24 Mp/sq. cm —> 2.0 micron pixels

[“enthusiast” compacts, e.g Panasonic LX3]

  • 16 Mp/sq. cm —> 2.5 micron pixels

[Fujifilm F31fd, circa 2007]

  • 5 Mp/sq. cm —> 4.3 micron pixels

[New micro Four Thirds models]

  • 3.3 Mp/sq. cm —> 5.5 micron pixels

[typical APS-C sensor DSLR]

  • 1.4 Mp/sq. cm —> 8.5 micron pixels

[professional Nikon DSLR]

Now, for the reasons I’ve vented about before, the smallest pixel that makes any sense to me is about 2 microns across. Making cameras pocketable dictates smaller sensor sizes; but unless the chip is under 24 Mp/sq. cm, you’ll definitely compromise low-light capability.

But the real leap in quality comes when you drop to “single digits” in pixel density. Even compared to enthusiast compacts, those DSLR-style pixels have 5 to 8 times the light-gathering surface. That really makes a difference.

What this world needs badly is more little cameras with big pixels. I hope we get some soon.

*Note I’m really quoting the “pixel pitch.” Each actual pixel loses a bit of light-gathering area to its wiring traces. But microlenses overtop give nearly 100% coverage; and so they’re really the relevant width in terms of light-gathering area.


11 Responses to “How Big Are My Pixels?”

  1. robert e Says:

    Just a geometry niggle re the F31fd: Fuji’s claim was that the hex-shpaped pixels and layout of the Super CCD HR allowed them to stuff more and/or bigger pixels per area than the rectangular grid, so interpolating pixel size the same way seems a tiny bit unfair to one party or the other, if ultimately irrelevant to your point.


    • petavoxel Says:

      That’s a fair point—I had forgotten about Fuji’s hexagonal pixels.

      But while that gave Fuji a better fill-factor compared to the competition 4 years ago, today sensors have microlenses that capture light over the whole sensor area. So it seem fairer to compare everything assuming 100% coverage.

  2. petavoxel Says:

    Another thing I like about quoting pixel size: Since marketers seem to adore “more is better” numbers, maybe we could get cameramakers to compete on THAT spec, rather than on empty megapixels.

  3. Hans Says:

    Hi! I fully agree with your post. Taking Robert’s earlier comment a bit further. One might say that pixel technology is advancing, do you think that technologies like Fujifilm’s EXR, Sony’s Exmor, Sigma’s Faveon, will be able to ‘save’ more pixels from smaller sensors?

    • petavoxel Says:

      I think it will be possible to wring out a few more improvements in pixel efficiency, maybe from back-illumination or something. Perhaps even 50% better— I don’t know.

      But that pales in comparison with differences in pixel area. If you jump from a 10 Mp P&S to a micro Four Thirds camera, each pixel has 640% more light-gathering surface. If you go from µ4/3 to a Nikon D700, that’s another jump of 390% in area per pixel.

      Bigger pixels win.

      • Hans Says:

        Thanks for the reply. Yes, it’s unfortunate that most of such technologies are used to counter the effects of more megapixels 😦

  4. Principia Says:

    So taking all of this into account, for those of us who are looking for something in the average consumer price range rather than Micro Four-Thirds or DSLR territory, *are* there any current point-and-shoots you would recommend based on your criteria?

    • petavoxel Says:

      Principia, you’re hardly the first person to ask this question. And unfortunately, this is exactly the problem: Manufacturers have taken away all the options with a sensible megapixel count.

      Size, Price, Quality: Pick two!

      Best image quality per dollar: Sorry—DSLR by a wide margin. Olympus E-520 is probably the smallest & cheapest (US$420).

      Best pocket-size: With some reservations, Panasonic LX3, Canon S90.

      Cheap & small: Lots of choices but little choice. I might start with Panasonic or Canon and look for a closeout on last year’s 8 Mp model. Don’t spend much.

  5. bshor Says:

    I have both the Fuji F30 and the Pentax K-x. The F30 looks positively ancient these days, and I hate the memory chips. But it took great low light pics. On the other hand, it doesn’t take HD videos, which my new Panasonic ZS3 does.

    Since the Panasonic, and other similir point-n-shoots, takes only 720p video, doesn’t that much smaller pixel count in taking video avoid the overloaded pixels issue you discuss? More broadly, if I lower the pixel count for photos, do we get around the issue?

    • petavoxel Says:

      if I lower the pixel count for photos, do we get around the issue?

      That’s the question everyone asks (here and in comment threads elsewhere). So-called “pixel binning” will probably not lose much true detail—try taking photos at all the different res settings and see.

      On the question of noise, that’s harder to predict. It depends how intelligently the camera does the downsampling. Compared to the melding of adjacent pixels which happens anyway when you look at your photos onscreen (unmagnified) or in a print, it may be a wash. Again, test your own camera and see what you think.

  6. […] of this scourge, I’ve needed to pore over DP Review’s specs listings—noting the pixel density of every model introduced since January, 2008. (There were about 450 in […]

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