A megapixel (mp) is simply one million (1,000,000) pixels or dots, forming a photographic image.
A 1 mp image can be of several formats, i.e. that several combinations of width x height can give the same number of megapixels. 5000×200 pixels, 2500×400 pixels or 1250×800 pixels are all 1 mp images. However, as the images tend to be rectangular and to respect certain standard formats, like the 4:3 image ratio. Other popular ratios are 3:4 or 16: 9 (same as the hd TV screens). This imposes some constraints on camera manufacturers. But, on some cameras, the photographer can select the desired image ratio.
More Megapixels = more information
The higher the number of megapixels is, the more an image contains information. So it will be more detailed. Most modern cameras have sensors that give images around 8 to 10 mps. High-end devices, get up from 12 to 24 mps approximately. Some really high end studio cameras can even go into the 50 mps range!
The megapixels race
Gradually, as the capacity of digital cameras increased rapidly, manufacturers began promoting the number of megapixels as a measure of the quality of the images produced by their cameras. But it’s important to remember that megapixels is only one factors, among many, that determine a digital image’s quality. Other factors are lens quality (sharpness), sensor size, noise, and many more.
You can not add information to an image
One important thing to understand: It is easy to reduce the amount of information in an image. But it is impossible to do the opposite. If I reduce the size of a large image to that of a postage stamp, then re-enlarge it to its original size, I will get a blurred image, without any details. Here’s an example: Reducing image size to 10% eliminates 90% of the information, which cannot be subsequently restored.
Note: In this demonstration, the quality reduction is only clearly visible on a computer screen and not so much on a tablet or a telephone screen.
Click to enlarge – Reducing the size of the picture to 10% eliminates 90% of the information. Which can’t be restored later. Image © Charles Martel 2015
Why is this? It’s because reducing the image’s size, (e.g. the actual number of pixels, not just the on-screen size), reduces the amount of information contained in it. Then enlarging it again, only multiplies the existing pixels that are left, without recreating the lost information. So if, initially your device has a low resolution sensor, it will be impossible to increase it thereafter.
Other factors affect the image’s quality
However, it is very important to understand that the number of megapixels is only one of many factors determining the quality of the image.
Other important elements are:
- the physical size of the sensor,
- The quality of the lens,
- The data processor (computer) in the camera
- The quality of processing,
- The cleanliness of the camera’s components,
- The sophistication of post-processing software used,
- The vision and technical capabilities of the photographer,
- etc.
Upcoming articles will cover these in more details.
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© Charles Martel 2015