Size Matter, Especially with Pixels

We all know numbers can be misleading. That’s one reason people usually think the more pixels a camera has, the better its pictures. But that’s not necessarily true. Lots of things affect the quality of pictures, including the design of the sensor, the data processing that happens in the camera, whether there’s compression and how much, the quality of the attached lens, the exposure, the size of the pixels and of course, the software you use if you’ve shot RAW. Of all those, the size of the pixels may be the most important, and the least understood.

Simply stated, pixels capture light and turn it into data. That data is made up of both good and bad information. The bad information is what we refer to as “noise,” which results in lower color saturation and a grainy, or textured look to the image. All pixels collect the same amount of noise, but larger pixels collect more of the “good” data than smaller pixels. With all else equal, a larger pixel will result in a higher quality image (less noise) than a smaller one. As we raise the ISO of our cameras, that noise rises too, making it more visible. That’s why if you want to get the best quality out of any digital camera, you want to shoot at the lowest ISO possible. And if you have to raise the ISO, then the larger the pixels, the better chance you’ll have of still getting high quality images. So despite what most people think, fewer pixels can sometimes mean better quality pictures.

The Nikon D4, with ONLY 16 million pixels, lets me shoot at astronomical  ISOs, 8000 in this case, and still get good quality photos. Photo copyright Reed Hoffmann.

The Nikon D4, with ONLY 16 million pixels, lets me shoot at astronomical ISOs, 8000 in this case, and still get good quality photos. Photo copyright Reed Hoffmann.

Once you understand this, sensor size starts to play a more important role. Obviously, larger sensors have more surface area, so larger pixels can be used. But that’s not always done. And if you have a really small sensor, and want to have a high pixel count, then you’re going to have to use really, really small pixels. Generally speaking, the smaller the camera, the smaller the sensor. Of course, the smaller the pixels, the harder it is to get great quality. If you thought pixels were hard to understand, then tighten your seatbelt. Sensor sizes vary widely, and can be difficult to make sense of. David Pogue of the New York Times wrote a story a couple of years ago that’s still very good at helping understand the confusion around sensor sizes. This is one reason I’d rather think about how large the pixels are on a sensor, rather than how many. Having massive numbers pixels isn’t always helpful (camera phones are a good example here), but there are some times where that becomes very important.

There’s one big advantage to having lots of pixels – pixels equal resolution. The more pixels you have, the more resolution. Think of resolution as information. The more information you have, the finer detail you can capture. The more information, the larger you can print a photo. The more information, the more you can crop a photo and still have enough information (resolution, or pixels) for a good quality picture. So what you really need to understand is how many pixels you need for what you want to do. For example, if 16 X 20 is as large as you’d ever print, then a six-megapixel camera would do the job. If you like to crop, or make poster prints, then 12, 16 or even 24-megapixels might be best. But if all you ever do is share photos online, to be viewed on computer screens, then even six-megapixels could be overkill.

Having 36-million pixels from the Nikon D800 for this shot meant I had no problem making a 36-inch print from it. Photocopyright Reed Hoffmann.

Shooting this scene of the Great Wall of China on the Nikon D800, with its 36-million pixels, meant I had no problem making a beautiful 36-inch print from it. Photo copyright Reed Hoffmann.

The big difference here is the amount of information you need for prints versus screen. To make good prints you need more information (resolution) than screens. For example, the 24-inch monitor I’m sitting in front of now has a resolution of 1920 X 1200. That means a two-megapixel image would completely fill it. For a print that size (roughly 12 X 19), I’d want to have around

I'm only using this picture online, so only need it to be 700-pixels wide. Click on the photo to see it that size on your monitor. Photo copyright Reed Hoffmann

I’m only using this picture online, so only need it to be 700-pixels wide. Click on the photo to see it that size on your monitor. Photo copyright Reed Hoffmann

six-megapixels. If you mainly upload photos to Facebook, there’s a good chance those images are being displayed at only 600 or 800 pixels (or even less) on their maximum dimension.  So screens don’t need many pixels, and even when printing, at most common sizes, massive numbers of pixels aren’t always necessary. As people started to realize that, cameras started to change.

One of the first big moves to away from the megapixel race happened a few years ago when Nikon introduced their first “full-frame” cameras (designated as “FX”), the D3 and the D700. The most surprising news wasn’t that Nikon was now making a full-frame camera, but that they were only putting 12-million pixels on the sensor. They could easily have put many more, and that’s what their competitors were doing. But Nikon chose instead to use fewer pixels, which let them use larger pixels. By now, hopefully, you understand the value of that. For photographers who regularly shot in low light, or sports, where high ISOs were a must, this was a breakthrough design decision. By going the route of fewer pixels on a larger sensor, Nikon made a camera that no other could compete with in poor light. And Nikon’s decision paid off in the number of photographers who bought those cameras.

Now that you understand this, you’re probably wondering what size pixels your camera has. While each manufacturer releases that information somewhere in the technical specifications for each camera, I’ve found the Digital Camera Database to be an easier way to find locate this. “Pixel Pitch” is the number indicating the size of the pixels, and it’s measured in microns. I did that recently for several different Nikon cameras I’ve used, along with a couple of the “best”camera phones. Here are those numbers, from high to low:

D700 – 8.45 microns, FX, 12MP

D4 – 7.3m, FX, 16MP

D600 – 5.9m, FX, 24MP

D800 – 4.88m, FX, 36MP

D7000 – 4.78m, DX, 24MP

D7100 – 3.9m, DX, 24MP

D5200 – 3.9m, DX, 24MP

D3200 – 3.84m, DX, 24MP

V2 – 2.86m, CX, 14MP

V1 – 3.39, CX, 10MP

Coolpix P7700 – 1.86m, 12MP

iPhone 5 – 1.75m, 8MP

Samsung Galaxy S3 – 1.4m, 8MP

This chart shows you comparative sizes of the sensors found in many cameras today. The smallest, 1/3.2, is what the iPhone 5 uses. Copyright Reed Hoffmann.

This chart shows you a comparison of the different size sensors found in many cameras today. The smallest, 1/3.2″, is what the iPhone 5 uses. Copyright Reed Hoffmann.

But just as number of pixels isn’t the most important factor, you can’t simply take pixel size as most important either. For instance, the Nikon D4 produces better high ISO images than the Nikon D700, which has fewer and larger pixels. Why? The D4 is newer, and manufacturers like Nikon are constantly improving both sensor design and image processing. The same thing’s true when comparing the new Nikon D7100 to the older D7000. Images shot under the same conditions, at the same ISO, show less noise with the newer D7100, despite the fact that it has more, and thus smaller, pixels.

Same scene, at 4000 ISO with two different cameras. Viewed at 100% magnification, you can see that the 7100 has more pixels (larger image) and better noise performance than the older, though larger and fewer pixel camera, the D7100. Click to see the image full size. Photo copyright Reed Hoffmann.

Same scene, at 4000 ISO with two different cameras. Viewed at 100% magnification (click image to view this), you can see that although the D7100 has more, though smaller, pixels, it also has better noise performance than the older D7000. Photo copyright Reed Hoffmann.

So what’s all this mean? Taking sensor size and pixel size into account when buying a camera is a balancing act. Larger sensors can offer better quality, especially at high ISOs if using larger pixels. But that also means a more expensive camera and larger, often more expensive lenses. The key is in understanding the different things that affect image quality, and how they will affect your photography. While there is no one camera that does everything best, with a little knowledge, you can find the right camera for what you want to do.