Almost every modern user of PCs and mobile gadgets is roughly guided by the resolutions of anything and is able to distinguish by the number of pixels the camera with the best matrix, the monitor with the best picture and the video with the best quality. However, when transferring content from “digital” to living paper, many have problems.
Actually, the catch lies in the fact that when printing, we have a new variable that the average user is not familiar with – print resolution. Only a narrow specialist engaged in printing, advertising, photo printing, etc., can easily name the minimum required resolution to create a physical image on a huge billboard, a small business card or a T-shirt with a print. In this article, we will focus on common examples of printing that each of us may encounter in everyday life (printing on A4, A3, A2, A1, A0 sheets), and also derive a simple formula for calculating the required resolution for any given task …
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What is DPI
So, print resolution is measured in DPI (dots per inch), that is, in dots per square inch (1 inch = 25.4 mm). The easiest way to explain this parameter is using an example of the principle of operation of such an outdated device as a dot matrix printer – in this case, DPI corresponds to the number of strokes of the needles with ink in an area of 1 × 1 inch.
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How many pixels are needed for quality print
Naturally, the DPI parameter does not matter at all as long as the image stays on your monitor, but the resolution of the source file is critical. You will not be able to print a photo quality on A4 paper at 300 DPI if the original image on the screen has a resolution of 1024 × 768 pixels.
Standard DPI values used in printing
Resolution 75 DPI – for text documents;
Resolution 150 DPI – minimum quality for printing images;
300 DPI is a common quality for photo printing.
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What is the size in pixels for A5, A4, A3, A2, A1, A0 sheets depending on DPI?
Below you can find the correspondence between the resolution values of the original image and the size of the sheet of paper on which you are printing (the data is calculated for print resolutions of 75 DPI, 150 DPI and 300 DPI).
A5 format size (148 x 210 mm) in pixels
at DPI = 75, the resolution of the A5 format has 437 × 620 pixels;
at DPI = 150, the resolution of the A5 format has 874 × 1240 pixels;
at DPI = 300, the resolution of the A5 format has 1748 × 2480 pixels…
A4 size (210 x 297 mm) in pixels
at DPI = 75, A4 resolution has 620 × 877 pixels;
at DPI = 150, A4 resolution has 1240 × 1754 pixels;
at DPI = 300, A4 resolution has 2480 × 3508 pixels…
A3 size (297 × 420 mm) in pixels
at DPI = 75, A3 format resolution has 877 × 1240 pixels;
at DPI = 150, A3 format resolution has 1754 × 2480 pixels;
at DPI = 300, resolution of A3 format has 3508 × 4961 pixels.
A2 format size (420 × 594 mm) in pixels
at DPI = 75, the resolution of the A2 format has 1240 × 1754 pixels;
at DPI = 150, the resolution of the A2 format has 2480 × 3508 pixels;
at DPI = 300, the resolution of the A2 format has 4961 × 7016 pixels…
A1 format size (594 x 841 mm) in pixels
at DPI = 75, A1 format resolution has 1754 × 2483 pixels;
at DPI = 150, A1 format resolution has 3508 × 4967 pixels;
at DPI = 300, A1 format resolution has 7016 × 9933 pixels…
A0 format size (841 x 1189 mm) in pixels
at DPI = 75, resolution of A0 format has 2483 × 3511 pixels;
at DPI = 150, the resolution of the A0 format has 4967 × 7022 pixels;
at DPI = 300, resolution of A0 format has 9933 × 14043 pixels…
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How is the number of pixels corresponding to the size of the paper determined?
As mentioned above, a print resolution of 300 DPI is considered to be sufficient quality for transferring graphics to paper. To print a photo or just a picture in this quality on an A4 sheet (297 × 210 mm), you need to have an original image with a resolution of 3508 × 2480 pixels, if the quality requirements are halved to 150 DPI, then the original resolution of 1754 × 1240 pixels will be sufficient. and for printing text, 75 DPI and a resolution of 877 × 620 pixels are enough.
In any non-standard situation, you can resort to forbidden techniques and use mathematics. For example, to find out the required resolution of the original image for printing, we can build the following formula:
R = L × DPI / 25.4
R – the required permission of the party;
L – side length in mm;
DPI – the required print quality;
25.4 – convert inches to centimeters (1 inch is approximately 2.54 cm) and multiply by 10 to convert to millimeters.
You need to print the image at 150 DPI on A4 paper (297 × 210 mm). We get:
R (height) = 297 × 150 / 25.4 = 1754 pixels;
R (width) = 210 × 150 / 25.4 = 1240 pixels.
Accordingly, the original resolution should be 1754 × 1240 pixels, which matches the data in the above table.