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Smartphones are rapidly hitting the point that, unless you’re planning to game or try to mine Bitcoins 5 Ways You Can Make And Mine Bitcoin Currency 5 Ways You Can Make And Mine Bitcoin Currency The revolutionary and controversial method of payment has been making headlines. There are plenty of reasons why you might want to start performing transactions using Bitcoins. But first, you have to earn some for yourself. Read More with them; the screens, processors, and memory are plenty sufficient for any application you have in mind. So, when it comes time to upgrade, more and more people are looking at the phone’s cameras as a differentiating factor. 

As those people riffle through specification sheets and stare blankly at impressively chipper salespeople, they may find themselves silently wondering, “What the heck is a megapixel, and how many do I need?”

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Megapixels are one of the most common ways of advertising the quality of cameras, especially relatively low-end cameras aimed at the mass market likes the ones in typical smartphones. This is unfortunate, because these days the megapixel count is far from being the most useful measure of camera quality.

Megapixels work like this: Uncompressed image resolution has two fundamental measurements: horizontal and vertical resolution. In other words, if you take an image and begin counting pixels across or down from one corner, you can multiply those two figures to get the total number of pixels in the image. More pixels, in general, give you a higher resolution picture. That’s where megapixels come in. A megapixel is, literally, one million pixels in the final image. 

In order to compute how many megapixels a camera produces, you simply multiply the horizontal and vertical resolutions of the sensor, and divide the result by a million. A 1000×1000 image, for example, is one megapixel. A 1920×1080 image is a little more than two megapixels. A 4k image is more than eight megapixels. So why aren’t megapixels the end-all be-all of camera quality? For starters, there are steeply diminishing returns. The jump from one to two megapixels is huge: it’s the jump from SD to HD that we went through few years ago — the number of pixels per square inch doubles. The jump from five megapixels to six, though, is less impressive. The pixels per square inch only increase by 20% – barely perceptible. The added pixels are scattered across a much larger image. This is all assuming, too, that you even have hardware that can display a high megapixel image, an unlikely proposition for any image above about four. On top of that, not all pixels are created equal.

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What Measure Hath a Pixel?

The way that point-and-shoot and smartphone cameras work is fairly straightforward: they use a simple lens to focus light onto a sheet of glass made of red, green, and blue elements, arranged in little clusters. Behind this glass sits a cheap image sensor, made of small silicon elements that register the intensity of light hitting them. The colored glass sheet filters out different colors to different sensor elements, so by measuring the disparity between the light detected under the different bits of colored glass, the computer in the camera or phone can deduce what color each pixel’s worth of the image is actually displaying.

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However, there are a couple of limits here: every image sensor element comes with a certain level of noise: random values that occur in the sensor regardless of the actual exposure to light. Engineering sensors that have lower noise level is hard and more expensive. For larger sensors (say, in a low-resolution camera), this isn’t a problem, because enough light is hitting the sensor that it easily drowns out the noise (this is why most phone cameras produce noisy images in dark rooms). However, as the individual sensors get smaller and smaller, less light hits them, and it becomes more and more expensive to drop the noise level down to an acceptable level. In the interest of pushing megapixel counts as high as they can for advertising purposes, many manufacturers simply allow the noise level per-pixel to increase – decreasing overall image quality, despite a larger number of megapixels.

To further exacerbate the problem, as resolution increases, the quality of the lens becomes a bottleneck as well. Cheap lenses introduce a degree of blurring, and increasing an image sensor’s resolution above the quality of the lens adds more pixels, but there isn’t much new information being added for those pixels, because the relevant information is being scrambled by the lens.

Worse, the poor ratio of lens quality to sensor resolution can produce color bleeding: light that’s gone through one color filter can wind up hitting the light sensor corresponding to another color, reducing the accuracy of the color in the final image and producing a gray, washed-out picture. You can see these effects yourself by taking a photo from a cheap but high megapixel camera and blowing it up on a screen to its native resolution. You’ll notice color artifacts, blurring, and generally that the image looks considerably worse than it does when scaled to fit on the screen.

All this is is unfortunate, because there are fundamental limits to how good a conventional lens of a given thickness can be. That why some smart devices, like the Galaxy Camera that we reviewed last year Samsung Galaxy Camera Review and Giveaway Samsung Galaxy Camera Review and Giveaway If you love your smartphone's camera, and want to take things up a notch, the Galaxy Camera is perfect for you. Running Android 4.1.1 (Jelly Bean), the Galaxy Camera is the exact opposite of what... Read More , have taken to including full-sized lenses.

How To Pick a Good Camera

So, let’s say you want to buy a phone with a great camera. If megapixels don’t matter, what should you be worried about? The answer is color accuracy, low-light performance, and lens quality. Unfortunately, it can be hard to find those specifications from phone manufacturers, so often the only answer is to look at reviews by technically literate blogs. If sample shots are provided, you can blow them up to get an idea of what the images look like at native resolution. This will give you an idea of the quality of the pixels that you’re getting, and not just how many of them. Right now, the market leader in phone cameras is Nokia, whose Lumia series of phones contain high-quality (if bulky) lenses and produce good results (though they are correspondingly pricey). The Lumia 1020 (which we reviewed Nokia Lumia 1020 Review and Giveaway Nokia Lumia 1020 Review and Giveaway Is it a phone? Is it a camera? No, it’s the Nokia Lumia 1020! Read More ) is a good bet right now for producing near DSLR-quality photos in a phone camera. On the IOS side of the things the iPhone 5s camera is also of a high output quality.

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Looking into the future, there’s a lot of reason to be excited about the new Pelican Imaging cameras, which use a grid of conventional cameras (each of which capture only a single color to avoid fringing) combined with clever software to produce images of much higher quality than is possible with normal smartphone camera setups. As an added bonus, the setup also captures in native 3D, and can be manufactured more cheaply than regular smartphone cameras. These devices aren’t out yet, but are expected to hit the market within a year, and represent a major shift in the quality possible for phone cams, so keep an eye out.

So that’s the lowdown on megapixels. Hopefully, you’ll now be little more prepared to make informed camera buying decisions. Let us know how your camera performs in the comments, and what brands you prefer for their camera quality!

Image credits: “Reflex Camera” by Markus Spiske, Sony DSC S650 (2007), by Alistair Paterson, Olympus e510 MOs Image Sensor, by Carlos Sancho, Nokia Lumia 1020 by Karlis Dambrans

  1. Suleiman O
    July 15, 2014 at 8:01 pm

    @Howard B Donno donnoo wa wa wat it is...search moi.

  2. Suleiman O
    July 7, 2014 at 1:10 pm

    Good read. What about Samsung Galaxy Note 3's 13 MB camera that has 4K technology ability?

    If we bring a 13 MB regular point and shoot camera against 13 MB cellphone camera, will the end result be the same?

    Does the size of the lens matter for cameras that have equal Megapixel output.

    Do all cellphone cameras have " cheap image sensor" ?

    Can a high end cellphone camera, like Samsung Galaxy Note 3, compete with entry level SLR cameras?

    • Andre I
      July 8, 2014 at 2:36 am

      If you were to take a regular point and shoot camera and a cellphone camera and compared the quality of pictures taken under similar conditions, you'd probably find that, on average, the point and shoot took better photos. That's not a hard and fast rule, of course, but point and shoot cameras can use bigger sensors and bigger lenses, and generally have an easier time taking higher-quality photos.

      As far as lens size, bigger lenses and sensors generally allow you to take higher quality photos given similar engineer time investments and component costs. Smartphones have a variety of image sensors in them, but the vast majority of them trend towards the cheap end due to the (very narrow) margins on smartphone hardware.

      SLRs tend to have a marked advantage over even high-end smartphone cameras, but that gap has narrowed recently, and will continue to shrink in the future. I suspect that some modern smartphones can probably outperform very cheap or old DSLR cameras. What it boils down to, I think, is whether or not the phone you're looking at takes photos that are good enough for your purposes. As the saying goes, the best camera is the one that you've got with you.

    • Howard B
      July 10, 2014 at 2:54 pm

      What's a "13 MB camera"?

  3. Howard B
    July 6, 2014 at 5:59 pm

    "A megapixel is, literally, one million pixels in the final image. "
    I beg to differ.
    Originally, in the computer world, at least, prefixes such as "kilo," "mega," and "giga" meant multiples of 2^10: 1KB = 1024 bytes (2^10), 1MB = 1,048,576 bytes (2^20, or 1024 x 1024), 1GB = 1,073,741,824 bytes (2^30, or 1024 x 1024 x 1024).
    Then hard drive manufacturers decided they could make their hard drives look bigger by making 1MB = 1,000,000 bytes. So "decimal megabytes" was born.
    Oddly enough, though, hard drives were pretty much the only thing that used "decimal megabytes;" if your 1GB RAM stick had 1,000,000,000 bytes, your PC WOULD NOT BOOT. It would fail RAM testing before your monitor even lit up. Decimal megabytes is nothing more than a marketing scam, and saying "1 megapixel = 1,000,000" pixels is just perpetuating this scam.
    Tech journalists tried to fight this the wrong way, creating "explicitly binary prefixes" by adding a lowercase "i" - KiB, MiB, GiB - instead of discrediting the HD manufacturers' interpretation, which sucks: The "decimal megabytes" numbering was allowed to continue.
    Note that this scam doesn't extend to SSDs or memory cards: Memory cards that aren't a power of 1 MB (binary!) don't exist, and SSDs that aren't a power of 1MB are because of reserved space for "replacement blocks" (a 120GB SSD is 128GB with 8GB reserved).

    • Jackson
      July 10, 2014 at 3:18 am

      In this case, mega does mean 10 to the power of 6.

    • Howard B
      July 10, 2014 at 2:47 pm

      @Jackson:
      "In this case, mega does mean 10 to the power of 6."
      In whose definition? Who sets the standards?
      If there was a standards body for those definitions, it would help a lot. I could say a 1024 x 768 image was "one megapixel" because it was "close enough."

      PS: Why isn't there a "Reply" button on your reply? I can only reply to my original post; does that mean that I *am* replying to myself, and you'll never see it?

  4. Hildy J
    July 6, 2014 at 4:42 pm

    The article is useful and relevant when it comes to smartphones. However, people should be aware that the jump to actual cameras introduces a new variable - the size of the sensor chip.

    A larger overall sensor chip allows each pixel sensor to be larger, potentially increasing its accuracy and reducing noise. You can read all about it in Wikipedia (http://en.wikipedia.org/wiki/Image_sensor_format). The trend for good cameras seems, to me, to be towards "full frame" (the size of a 35mm film frame with a 3:2 aspect ratio) and "four-thirds frame" (whose name does not refer to the size, it's smaller than full frame, but to the 4:3 aspect ratio).

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