Did you hear about the HTC One's fancy new "UltraPixel Camera"? HTC touts the camera as an end to the "megapixel wars." UltraPixels! Revolution! And, yes, the technology sounds very promising, but, uh, wait a second, what is an UltraPixel anyway?
HTC's new phone only has a 4-megapixel camera, and that could lead people to think it's inferior to the (roughly) 8-megapixel cameras on competing phones like the Nokia Lumia 920 and iPhone 5. Indeed, huge megapixels counts have long been used to trick customers into thinking that one camera is more sophisticated than another. The solution? Rewrite the language? Or maybe just confuse people more with another meaningless term.
HTC really wants you to know that its megapixels are BIGGER than the megapixels on competing cameras. That's why they're so ULTRA, get it? Fewer pixels on an identical surface area means the pixels are bigger. Both the HTC One and Lumia 920 have a 1/3-inch sensor, but the 920 has 8.7-megapixels compared to the HTC One's 4MP. That's why the HTC One has larger 2-micrometers pixels whereas the 920 only has 1.4-micrometer pixels.
Size matters. Image sensors are covered in photodiodes, which convert light into electricity, which is processed and recorded as data. Each pixel in your photo represents one photosite on the sensor.
When you take a picture, the camera's shutter flies open for a fraction of a second letting photons pour in. Bigger photosites can capture more photons, and thus, capture more data. The difference is especially pronounced in conditions where the light sucks.
More data means more quality—to a point. You need enough pixels so that you can view the image at a reasonable size on screens. Think about how ridiculous a 100 x 100 image would look on the 1920 x 1080 on the HTC One's 1920 x 1080 screen. But then again, most cameras output photos way larger than what most people will ever need. The 4-megapixel camera on the HTC One outputs 2688 x 1520 images, and that's really dangerously small if you want to crop or edit your images at all, but HTC is gambling that it is good enough for most people. All you're doing is uploading photos to Facebook and Instagram anyway, right?
The resolution of a camera's image sensor is only one of many factors that affect image quality. The lens, image processor, autofocus, and metering all have to work well, too. That's why in our recent smartphone camera battlemodo, five cameras with nearly identical megapixel specs yielded such different results. Sure, the HTC One has an industry-leading (along with the Lumia 920) f/2.0 lens. But other than the favourably large aperture, we don't know if this camera—for all the hype—is really any good at all.