Great photos are hidden in your smartphone film, it's time to show them off! But before printing your photos in large, you must imperatively check if the resolution of the image is sufficient. Here are some tips to know the ideal resolution for the size of your print.
Definition: the resolution of an image
Resolution refers to the sharpness and quality of the image relative to the format . In the digital domain, it is expressed in ppi (pixel per inch): it is the number of pixels that are counted over a length of 1 inch (2.54 cm). In printing, we speak of dpi (dots per inch): it is the number of colored dots printed on 1 inch.
The optimum resolution for printing is 300 dpi ; that's 30 pixels per inch. For 150 dpi, there are 15 pixels per inch; the pixels are twice as big, so the image is less precise.
Resolution is often confused with definition. In fact, the definition corresponds to the size of the image in pixels (length x width), it is the total number of pixels that make up the image.
See the image resolution on my computer
Under Windows, all you have to do is right-click on the image, then access the "Properties" of the file, at the bottom of the list. In the "Images" section of the "Details" tab, you can see the definition and resolution of the photo. However, the resolution is displayed only for ".jpg" files.
On Mac, double-click on the image, then "Show annotation toolbar" by clicking on the pencil icon, next to the search bar. Finally, when you click on the “Adjust size” icon, a tab appears with the definition and resolution of the image.
What is the ideal print size for my photo?
The quality of the print will depend on the resolution and definition of your photo. You know the size of your image in pixels, but you do not know what format it corresponds to on paper? There is a very simple formula to obtain the size in centimeters of your print: (definition * 2.54) ÷ resolution
For example, I want to print a 3264 x 2448 pixel photo with a resolution of 300 dpi. I calculate :
- (3264 * 2.54) ÷ 300 ≈ 27 cm
- (2448 * 2.54) ÷ 300 ≈ 20,7 cm
I now know that the ideal size to print my photo with a quality rendering is approximately 27 x 20.7 cm.
Calculate the minimum definition necessary for a quality print
Conversely, if we already know the print format, we can calculate the minimum definition necessary with this formula: (format ÷ 2.54) * resolution
For example, I want to print a photo in A4 size (21 x 29.7 cm) with a resolution of 300 dpi. I calculate :
- (21 ÷ 2.54) * 300 ≈ 2480 pixels
- (29,7 ÷ 2.54) * 300 ≈ 3508 pixels
To print my photo in A4 format with optimal quality, my digital image must be at least 2480 x 3508 pixels.
If you're not too comfortable with math, there are online converters that do the math for you!