Pixels
Digital photos consist of a large number of pixels. These points make up the smallest elements of a photo. In English these pixels are called ‘pixel’ (which is derived from picture element ie: image point). If you zoom in very far on a photo on the computer, the individual pixels will become visible as square blocks. So a photo that is ten pixels wide and ten pixels high has a total of one hundred pixels.
The size of a digital photo is not expressed in centimeters but in pixels. That’s because a digital photo has no dimensions. Only when a photo has been printed does it have a length and width in centimeters. More on that later.
Resolution
The size of a digital photo is therefore expressed in pixels. For example, one speaks of a photo of 800 by 600 pixels. This size is called resolution. One is then talking about a photo with a resolution of 800 x 600. This means that the photo is 800 pixels wide and 600 pixels high. This resolution determines how large the photo will appear on your screen. The more pixels, the larger the photo on your screen.
To print
What resolution should a photo have to get a good print? For that you need to know what dpi is. Dpi stands for dots per inch . dot is English for dot and inch is an English length measurement: 1 inch is about 2.54 cm. Converted 1 centimeter is 0.39 inch. Dpi stands for the number of dots printed per inch. The more dots per inch, the higher the quality of your photo.
If a printout contains approximately 300 dots per inch (300 dpi), then it is called photo quality. You can equate the points with the pixels from your photo. With this knowledge we can now calculate ourselves how large a photo should be, if it is to be printed properly at 300 dpi.
A commonly used photo size is 15 by 10 cm. Suppose you want to print a photo at this size at 300 dpi:
The width needed is: 15×0.39×300 = 1773 pixels.
The height required is: 10×0.39×300 = 1181 pixels.
If you have a photo that is larger than 1773×1181 pixels, then you are always in the right place. But if you have fewer pixels, the print quality will be lower.
This way you can also determine whether you can print your photo enlarged. Do you want to print a photo full screen on one sheet of paper? The normal paper size of a printer is A4 and the proportions are 29.7×21 cm. Not all printers can print borderless, but for the example we take the total A4 as a starting point.
We then arrive at the following:
29.7×0.39×300 = 3475 pixels.
21×0.39×300 = 2457 pixels.
You see, it takes a large file of 3475×2457 pixels to print the photo.
You can also settle for less than photo quality. Take a resolution of around 200 dpi as a lower limit: this still gives beautiful photos. If you print photos at less than 200 dpi, the result will always be mediocre.
crop
In addition to enlarging a photo, it can also be worth using part of a photo. You then crop the photo. In fact, you are left with a smaller photo. But you can print that smaller part enlarged, for example in the normal photo size of 10×15 cm. You are satisfied with a lower quality print and opt for printing at 200 dpi. That means your crop should be at least 1170×780 pixels in size. If you shoot photos with reasonable quality, for example 1800×1360 pixels, you can crop quite a bit: about 60% of the photo.
printing centers
You can have your digital photos printed at an online center. You then have to send the photos to the printing center via the Internet. The exchanges usually indicate clearly whether your photo has the correct resolution. Usually there are three grades: Excellent, Good and Pass. Always try to submit photos that fall into the Excellent category, then you can be sure that you will get beautiful photos. Read more about the best print center in our article ‘Which print center?’