If you have been looking at clipart for printing, or indeed, any graphics, you are likely to have seen reference to DPI.
DPI stands for Dots Per Inch and this tells us the quality of the clipart or graphics for printing or screen display. Digital images are made up of pixels, and in this instance, a pixel represents a dot.
This is a bit of an extreme demonstration, however, pixel art is a great example of this. When you look at the pixel art paw illustration, every pixel is clearly seen. This is likely to be a low-resolution file, with a low dpi. While this is great for pixel art and is often seen in computer games, it’s not great when you want a more smooth effect or where you need detail to be seen.
However, in this example, the chameleon is completely smooth, with crisp outlines. This is because he is a high-resolution file saved at 300 dpi. This means, there are 300 dots (pixels) for every inch, therefore when printed, the dots will be virtually invisible.
Why DPI Matters for Printing
DPI matters when printing. The resolution for screens is 72 dpi. However, if you used 72 dpi for a print file, it is likely to be fuzzy and slightly pixelated. You will not get good crisp lines on your print.
We most often use 300 dpi for printing to get good results. However, sometimes you will see prints with higher or lower dpi. This will largely depend on the end use. Printing a poster at 150 dpi will give adequate results for, say, a classroom poster or party invitation, however it might not work so well for a photograph with lots of tiny detail.
The printing quality will also differ depending on the surface. A photo will look very different printed onto photo paper, for example, than a t-shirt.
It’s important to note that the printer will have a part to play here too. While something may look a little fuzzy on one printer, may print great on another. Therefore it is always good to test before doing a bit print run.
How to Calculate Image Size
So, if you need to print, for example, a 10″ image, and you want to be high quality with no fuzziness and all the detail to be clear, you will need the image to be at least 3000 pixels tall.
If you are printing the image at 150 dpi, you will need the graphic to be at least 1500 pixels tall.
This is why we normally measure images by pixel size, not in inches or centimetres.
So, I Can Just Stretch The Image…??
Well, perhaps not a hard and fast ‘no’, but resizing an image to increase the pixels, won’t necessarily give you great results. While the difference might not be discernable if you are making a small resize, if you were increasing an image which is 300 px across to 1000 px across, you will likely see a degradation in your image quality.
Therefore, it is best always to check the image size before buying if you need a certain size printed version.
Most clipart creators, creating clipart for educational resources, will create clipart which will print between 4 & 6″. Some will create bigger/smaller, however as clipart for educational use will likely be inserted into letter/a4 paper, this is a good size.
Clipart for digital use (PDF, apps, websites etc), need only be 72 dpi.