In Smartphones a 5 megapixel Camera is Usually Better

I am watching the latest TWiT (This Week in Technology) video-cast as I punch up these couple of postings and Leo Laporte just covered a point that I found interesting. I was not surprised by their comments as the science behind why this is so is well understood and documented.

Basically they were saying that they find that smartphones with 5 megapixel cameras take ‘better’ clearer richer pictures than those phones with 8 or 10 megapixel cameras.

At about this point anyone reading this who has done any research on imaging sensors and photo-site density will be nodding their heads and saying to themselves “Yep. That’s right.”

The quality issue comes about because those smartphones with the larger 8 or 10 megapixel cameras have a sensor in them that is the same physical size as the sensor in the 5 megapixel smartphones (or at least very close to the same size). It is a well documented fact that as the photo-sites (pixels) get smaller (i.e., the pixel density increases) the quality of the capture falls off. The key reason for this is that significantly less photons are captured by each photo-site container on the sensor and many more photons get clipped on the edges of the photo-cites and are not captured.

The image sensors in phones range from 2.4mm x 1.8mm (known as a 1/1.6” sensor) up to 3mm x 4mm (known as a 1/3.6” sensor). Most smartphones with a 5 megapixel or denser sensor will be using the marginally larger 1/3.6” sensor. But even with the slight larger sensor the pixel density is extremely high.

An eight megapixel 1/3.6” sensor has a photo-site density of around 60 million pixels per square centimetre (60MP/cm²). A five megapixel sensor of the same size has a density of 40MP/cm², which is still high but is a third less dense than the eight megapixel sensor. Hence each photo-site on the five megapixel sensor will collect more photons and get a better ‘reading’ of the light coming into the camera with far less photons being clipped and lost. This results in a better overall capture of the scene being photographed.

It is highly likely in the years ahead that sensors in smartphones might get slightly larger but they will not get much larger because their size is governed by how far from the sensor the ‘lens’ can be positioned. And with mobile phones getting slimmer and slimmer the lens is not going to be able to get much further away from the sensor, which it must if the sensor is going to get larger.

All of the above is the reason that compact cameras and digital SLR (DSLR) cameras are not likely to be replaced by camera phones any time soon. The pixel density in a half decent compact camera is around 2oMP/cm². More expensive semi-compact camera have densities around 10MP/cm². The pixel density in a semi-pro DSLR is typically less than 5MP/cm² (the Pentax K-7 is 4 million/cm²). In a pro DSLR the pixel density will be under 3MP/cm² (the Canon EOS-1DSMkIII is 2.4 million/cm² and the Nikon D3S is 1.4MP/cm²).

So you can start to see why a camera phone is not going to get anywhere near the picture quality of a DSLR—not in the next ten or so years anyway.