Megapixels vs sensor size: which matters most?
Sensor size and megapixels come up a lot in any technical discussions about the merits of different cameras. They are related in a way because it can be good to have both, but in reality they are two separate factors in image quality that still get confused. Let’s un-confuse them.
Megapixels used to be the Holy Grail of digital photography. The more megapixels you have, the finer the detail your camera can capture – in theory. That was fine back in the day when ALL camera sensors were small and megapixels were a key differentiator.
The trouble is that if you have a small sensor, the individual photosites – the light receptors that go to make the pixels in the photo – are so small that they become less efficient. The more megapixels you have in the same-sized seensor, the smaller more inefficient they become.
You’ll often see a lot of smartphones with 48MP sensors that use a technique called pixel binnng, where groups of four pixels are combined into one, to produce 12MP images. 12MP is obviously a lot less than 24MP, but this produces better overall image quality. Where there’s an option to use the full 48MP, there are typically quality compromises that mean you don’t get the full benefit. These can include more digital noise, or only a small increase in actual detail recorded because there is a limit to what the lens can resolve optically.
This is a particular problem with small sensors like those in smartphones and point and shoot cameras. More megapixels sounds great, but in practice the small size of the sensor is the limiting factor for image quality.
Sensor size remains an important factor in image quality even with larger sensors, such as the 1-inch type sensors in some vlogging cameras through the Micro Four Thirds, APS-C and full frame sensors in regular cameras.
The first rule of thumb is that for the same megapixel rating, a larger sensor will give you better image quality. A 24MP full frame camera will give you less noise and greater clarity of detail than a 24MP APS-C camera. The differences may not be huge, but they will be there.
The second rule of thumb is that more megapixels is not always a good thing and can be counter-productive. How many megapixels do you need? That’s a topic for another article, but while cramming more and more megapixels into a same-sized sensor can yield more fine detail, it may be more detail than you need for your photographs, whether they’re to be posted only, printed and hung on your wall (printed how big?) or they’re being taken for clients.
More megapixels might get you more detail than you need at the cost of reduced performance in low light, slower burst shooting speeds and bigger file sizes. Maybe the compromise is worth it for the kind of work you do, but it still needs thinking about. For most photographers 24MP will be enough, but for those who like to produce large exhibition prints, have demanding commercial clients or just like to pixel-peep, 40MP, 60MP or even 102MP (Fujifilm’s GFX series) will be either attractive or essential.
The third rule of thumb is that you need to strike a balance between megapixels and sensor size. If you want more megapixels, fine, but it’s best if you go for a camera with a larger sensor if you do. For each given sensor size there seems to be a sweet spot where the megapixel rating is enough for good detail rendition without too many compromises in image quality.
For smartphones, that’s arguably around 12-16MP, and for point and shoot cameras 20MP looks about the maximum. MFT cameras seem to have stabilized at 20-25MP, while APS-C cameras range from 24-40MP – the 40MP APS-C sensor used by Fujifilm seems a bit of a stretch for this format, but it does deliver very good results. With full frame cameras, 24MP delivers very nice overall quality and good resolution, but you can also get 40-60MP cameras with very high resolving power and few quality compromises – but naturally these are more expensive.
The bottom line is, forget megapixels and look and the sensor size instead. Pretty well all cameras these days have enough megapixels, and sensor size is the true determination of image quality.
