The number of pixels available to the sensor of a camera is often put forward as a selling point by manufacturers or sellers.
However, having a sensor with a higher number of pixels is not necessarily a good thing. Depending on the photos you take, it will be better to choose a sensor that has fewer pixels, but each pixel has a larger surface area – something you are rarely told about when buying a device on the market.
Here are some explanations to better understand how many pixels you need on your device.
A sensor could for example contain 6,000 pixels across its width and 4,000 pixels across its height. 6,000 x 4,000 = 24,000,000 pixels. This camera will therefore have 24 Mega Pixels (usually rated 24MP).
When comparing different cameras, we usually compare the number of pixels. But what we forget to compare is the size of these pixels. Indeed, the larger these pixels are, the more efficient they will be because they are able to record more light and do so with better quality.
If you take two 24 Mega Pixel cameras, they both contain the same number of pixels. But if one of the sensors is a full frame and the other a micro 4/3, the pixels of the second will be half as large as those of the first. The surface of a micro 4/3 sensor is half that of a full-frame sensor. To fit the same number of pixels, we have to divide the size of each of these pixels by two.
So when comparing two devices, don’t stop at the amount of pixels. Also consider the quality of those pixels. A 24MP camera with a full frame sensor will have better quality than a 24MP camera with a micro 4/3 sensor.
Stitch Per Inch
Dots per inch (DPI) — also known as DPI from English Dots Per Inch — is a unit of precision that defines the resolution (usually of a printer or scanner).
The higher the number of dots per inch, the sharper the resulting image.
If you draw a line, at 50 DPI you begin to see a clear, well-defined line, at 300 DPI the line is perfectly sharp.
300 DPI is the limit of precision that the human eye can discern. It is therefore useless to go above 300 DPI. If you want to obtain a perfectly defined image, you have to get closer to 300 DPI (whether on a screen or for printing).
Print accuracy and viewing distance
The distance from which we look at a print or a screen has an influence on the amount of detail we need for the display.
The closer you are to the displayed image, the greater the definition will have to be.
A classic print (for a book or an exhibition for example) will be done at 300 DPI. But if your image is intended to be seen from afar, there is no need to go up to this resolution. To give you an example, an advertising poster intended to be displayed on top of a building can be printed at less than 15 DPI. With distance, no one will see the lack of definition.
How many pixels do you need in your device?
The number of pixels you need depends on what you are going to do with your photos.
When deciding, you should keep two factors in mind:
- The size of the images you want to create (will they be printed on A5, A4, A3 paper, a 4m x 3m poster?)
- The distance at which it will be seen (will the people who will see your images be physically close to them or not?)
Here are some sample displays to help you better understand the relationship between size, distance, and print accuracy needed to get your photo sharp:
Computers and TV screens
- For an image published on a social network so displayed in 600 x 400: 600×400 pixels = 240,000 pixels = 0.24 MP (yes, you don’t even need a megapixel).
- Retina Display laptop screen: 3840 x 2160 pixels = 8.3 MP
- HDTV: 1920 x 1080 = 2.5MP
- 4K TV: 3840 x 2160 = 10MP
prints
Small print (classic photo): 15 x 10 cm (6×4 inches)
- at 300 dpi = 1800 x 1200 = 2.1 MP
- at 240 dpi = 1440 x 960 = 1.4 MP
Medium print (for a large format book): 30 x 20 cm (12 x 8 in)
- at 300dpi = 3600 x 2400 = 9MP
- at 240dpi = 2880 x 1920 = 6MP
Poster print: 90 x 60 cm (36×24 in.)
- at 300dpi = 10800 x 7200 = 78MP
- at 240dpi = 8640 x 5760 = 50MP
Ideally for a poster you need a device with between 50 and 78 MP of definition, but in reality you can do it with a much lower definition, in particular by increasing the sharpness in post-production. Some photos taken with a 24 MP camera, very sharp lenses and retouched in post production manage to have a good rendering in poster printing.
When choosing your device, you must therefore bear in mind the maximum print size you will want to obtain.
For most people, with a 24 MP device, you’ll be able to make a nice impression at 64 x 43 cm (25 x 17 in). With 12MP you will have a print of 46x28cm (18×11 in)
One last thing, don’t worry too much about pixels when two devices are close enough. Between 20 and 24 MP, the difference will be minimal.
Advantages and disadvantages of having a lot of pixels
Depending on the use you will make of your device, it may be interesting to have few pixels, or on the contrary to have a lot.
Advantages of having fewer pixels (therefore bigger pixels)
- Best suited for low light conditions
- Faster bursts
- Photos take up less space on your memory card and hard drive
- Photo transfer is faster
Advantages of having more pixels (thus smaller pixels)
- Better resolution
- You can create larger enlargements
- You can crop more easily while maintaining good print quality
(If you want to buy camera equipment, you shouldn’t look for the best camera, but rather find the one that will best suit your needs. To do this, you must understand the market, know your needs, and then match them to know buy wisely. Choosing the right camera for your needs will save you money, allow you to progress faster, and help you improve your photos.