How Digital Cameras Work: The Megapixel Myth (part 2)
See the first part of this here.
The Megapixel Myth is one of the longest running misconceptions ever devised in photography. It was conceived by camera developers to try to create an empirical value on which consumers can (mistakenly) judge the value of a a digital camera. The myth states that the higher the number of megapixels a camera has the better the resolution of the images it produces are. In this part I will continue explaining the truth behind this misconception.
Pixel Size
This is one of the biggest aspects that denotes the resolution of an image you have captured. To fully understand this aspect you need to understand how an image sensor works (See this article for more information).
When discussing pixel size of an image sensor you are really talking about the size of the photovoltaic cells that make up the image sensor. These are the cells that convert light photons into electrical current, then into binary data. The size of each of these cells is very important in the collection of light to produce an image. Larger cells will allow more light to be captured by a single cell than with smaller cells, meaning there is more essentially more data created by each cell. There are many other technical aspects that denote the quality of the data created by a cell, but for now I will try to keep this as simple as possible. As more light is absorbed by a single cell you increase the signal that the cell transmits, meaning that you essentially decrease the noise associated with that cell.
Image Sensor. Image by infomatique
Pixel size is the primary reason why many smaller camera devices, such as cell phones and point and shot cameras may boast higher megapixel qualities but do not produce decent images, and usually contain high degrees of noise. Making smaller cells allows for more pixels to be captured by a smaller sensor, but also do not let sufficient light into each pixel. This causes pixels to not only contain more noise but also be inherently darker.
Image sensor. Image by John.E.Robertson
It is usually easier and more cost effective to produce an image sensor with smaller pixels because it is possible to cut multiple sensors from the same wafer. As you increase the size of the pixels and decrease the number of pixels on a sensor it begins to become more costly to develop, as you cannot cut as many image sensors from a single wafer.
The Mega Pixel Myth
So the final question left is: Are megapixel ratings an accurate method of measuring a camera’s quality. The final verdict is… Only a little bit. Yes, the number of megapixels can be important if you are wanting images of the highest quality but you also need to consider the size of both your image sensor and pixels on the sensor as well. These three aspects, along with your lens’s quality will determine the quality of any image you take. It only takes a 6 megapixel camera to create a good 8×10, so do not think you have to get the camera with the most megapixels to get the best results. Most of the time this idea will work against you.
A 12MP camera (D300) that will work wll for most people. Image by armno_old
Very good points in this article
Megapixels are very important for marketing but less interesting to define image quality.
As you point out in your article, you can get decent 8 x 10 prints with a 6Mp camera.
I made some 15×23 prints made with pictures taken with my old EOS 10D camera (6Mp) and have seen even larger prints made with such pictures when it was the only resolution available for DSLRs.
Sensor and pixel size are much more relevant factors than the number of Megapixels.
15×23 off a 10D that is impressive, good work