Megapixels is one of the most misunderstood aspects of camera performance. In general, the higher number, the better the performance right? Well, no. Not always. Here’s a quick rundown on what Megapixels truly mean for you.

First a quick primer. What is an image sensor? It is the part of your camera that captures an image by converting light to a digital signal.

Location of camera sensor

Location of camera sensor

Image sensors come in different sizes and aspect ratios. There are three competing standards: Full-Frame, APS-C, and Four Thirds.

Sensor size comparison

Size difference between the formats

The Practical Difference

For purposes of comparison we will pick the two extreme ends of the formats: Full-Frame vs. Micro Four Thirds.

Low Light Performance

One common marketing trick in promoting camera sensor capability is the term “Megapixels” or MP. You’ve probably seen it – 16MP, 33MP etc. A camera sensor consists of millions of tiny individual cells that measure one “dot” each. So a 16MP sensor has roughly 16 million dots that it can assign a light value to. All these “dots” collectively make up the image. So what happens when you have a 16MP Full-Frame sensor (Nikon D4S) go up against a 16MP Micro Four Thirds sensor (Olympus E-M1)?

They both have the same pixel count. So technically they should be the same in image quality, right?

WRONG. Each individual cell in Nikon’s sensor is actually larger than Olympus’. That’s why Nikon’s Full-Frame sensor is larger – because the cells are larger even though the cell count is the same. And because each cell is larger, it is able to collect more light. This is the key. What this means is that the Nikon D4S can perform far better in low-light situation than the Olympus E-M1 – even though both are 16MP in resolution.

At ISO 12800 (film speed) the D4S far outperforms the E-M1

Full-Frame far outperforms Micro Four Thirds in low light (courtesy of dpreview.com)

Resolution Performance

What if instead of packing larger cells for better low-light performance, Nikon packs smaller cells – closer to the size of the Olympus sensor? By doing this, they can effectively pack more cells into the same area. This is exactly what Nikon did with its very excellent Nikon D800 camera, reaching a stratospheric 36 Megapixels in resolution. The result is images that you can blow up to a wall, yet retain significant detail.

Original

Full-Frame original image (7360×4912 resolution) – click to see full size

Cropped

Cropped image (450×300 resolution)

Herein lies the challenge of large resolutions. Nikon’s excellent 36MP Nikon D800 carries a mind-blowing 7360×4912 pixel resolution. But as you can see from the cropped picture of Natalie’s face, I can get a very decent picture at 0.135MP. Yes. That about one-tenth of 1MP. In practicality, most users won’t see tangible benefits beyond 6MP.

Another disadvantage is that a Nikon Full-Frame image yields about 75MB in file size! And that’s one single image! You need more hard disk space and more powerful computer to post-process your pictures. Finally, Full-Frame cameras and lenses in general are significantly bigger and heavier than the other formats. So larger format camera systems carry size, weight and also cost disadvantage.

Conclusion

Understanding camera performance is not as simple as Megapixels. So in your next camera purchase, don’t chase the Megapixel race. Ironically, the oft-quoted maxim of ‘its not a matter of size, it’s how you use it‘ is true.

If you love taking pictures of your family in natural-light or low-light setting – without flash – and you love the flexibility of being able to crop images, then a Full-Frame sensor yields significant, practical advantage.

If all you do is sharing on Facebook and you never print a picture beyond 10R (10″ x 12″), then you very likely can live with APS-C or even Micro Four Thirds (MFT). You will get significant size and weight advantage (not to mention cost). While it does not perform as well in low-light settings, at smaller resolutions, it is not as critical.

Bottom line: If you want ultimate performance, go with Full-Frame. But for practical usage, go with the newer generation APS-C or MFT cameras. Their low-light performance have improved significantly and Megapixels don’t mean anything unless used in proper context.