What is DPI in printing and how does resolution affect print?

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You’ve prepared a beautiful design, it looks great on screen, and you send it off to the printer and wait for your project. When it arrives the print quality is not what you expect. Some of the pictures look grainy and pixelated so the print job is a mess, a nightmare!

There is a rule in print, “Sh!t in, Sh!t out”. The trick is to make sure your print files give you the best possible quality print and a good printer will be able to advise you on this. In this article, we explain what DPI is in printing and how it relates to the finished job.

Most printers, including Smart Printing Company, have systems in place to check the image resolution of the printed image before it gets to that stage. However it’s not always clear cut, so we have written this article to help you understand how to get the best results from your print project and avoid print disasters.

Definition: What does DPI stand for?

DPI represents (Dots Per Inch) and it’s the way graphics and print professionals measure the resolution and quality of an image. Images are made up of dots which can be seen under a magnifying glass and the dot density is measured by counting the number within a given area. In this instance the area is a square inch, hence the term DPI ‘Dots Per Inch’.

While there is a “standard dpi value” quoted by most printers, often this depends on the size of the finished image and its viewing distance. More on that later.

What is DPI and how is it used?

DPI is a measure of the resolution of an image. It allows graphic designers, professional photographers and printers to measure how good the final image will look. Typically, a lower DPI means a lower quality image, whereas a higher DPI will generate a better quality image.

However, there are exceptions, for instance, some Photoshop users will know that it’s possible to increase the DPI within the software but this does not improve the final image quality. This process, known as ‘upsampling’ just changes the size of the dot and usually makes the printed image look worse.

As a rule, it’s not possible to improve the quality of an original image so it’s best to take the best quality image possible and if a lower DPI is required then it could be downsampled accordingly.

DPI vs PPI resolution, what’s the difference?

PPI refers to Pixels Per Inch, which is a term used to express image quality on screen. It’s similar to dots per inch except it’s more accurate to refer to on-screen resolution as pixels.

Industry standards with DPI

300 DPI is often stated as the minimum resolution for print quality, However, the reality is that most printers’ actual print resolution is much lower. While 300 DPI stands as the optimum for high-end work and fine art productions, it depends on the printing device.

For example, some very high quality digital and inkjet printers can reproduce a very high printing resolution. Most marketers can use a DPI as low as 150 a reasonable benchmark (see the table below).

Low resolution – For on-screen viewing

On the internet, speed matters so web designers use lower quality images to allow the page to load faster. On a standard computer monitor the display resolution is much lower than printer dpi because images on the web are typically 72 DPI, which is why they are unsuitable for quality print.

Low resolution images are fast to process and take up a minimal amount of field space.

Medium resolution – For most print

At the risk of lowering the bar, images with 150 to 300 DPI resolution are not ideal but the truth is they can produce good results depending on the intended size of the image. For instance, a 150 DPI image may not be suitable for a full-page spread but would be fine for a picture image within a page.

Images that fall within this range will process quickly and won’t take up much file storage.

High resolution – Quality print

300 DPI resolution should be seen as the ideal resolution wherever possible, and a good digital camera is capable of even higher resolution. A good rule is to start with a high DPI as it can always be downsampled later in the process, for example, if the file is too large.

High-resolution images tend to be slow to process and take up a large amount of storage space, which is why some printers lower the resolution during the pre-press process.

The right resolution for each print

One important consideration is how the print will be used. As an example, a large format print which is designed to be viewed from a distance can work really well with a much lower resolution because the eye cannot pick up the dots from a distance. We have put together this chart to help you decide the right minimum resolution for you

Photos and images:

  • Fine art and high-end work
    • 300 DPI
  • Brochure work
    • 150 DPI
  • Small posters A2/A1/A0
    • 100 DPI
  • Larger work (signage and wall art)
    • 50 DPI

What’s the human eye’s visible resolution limit?

There is a reason 300 DPI is seen (no pun intended) as the optimum resolution for printers, and that’s because it’s about the limit of the human eye. While some people can distinguish higher resolution, the returns are ever diminishing, and these extremely detailed files can slow down file handling and even cause other issues in the pre-press process.

Other factors that influence print quality

DPI is not the only factor when it comes to producing quality printed materials. Factors such as paper, the line ruling (Lines Per Inch or LPI) that the printer uses, along with colour profiles and space used in the artwork RGB, CMYK, using the correct bleed, and the quality the printer prints can make all the difference! We cover some of these in a bit more detail below.

Print Quality

Sometimes this is affected by the printers attention to quality but to be fair many printers (not all) attempt to do a good job with the machines they have. The difference comes down to the capability of the machine. For example, a quality inkjet printer can reproduce astoundingly high resolution but often an eyeglass is needed to appreciate the density of printed dots per inch.

Therefore quality beyond 300 dots per inch is often not recognised on the printed page, but the quality can be negatively impacted by factors such as excessive dot gain, the printer resolution, the printer using more ink than is required or simply having a limited range of capabilities and therefore not printing the best dpi for the job.

Laser printers print in a random dot, but often the look of the finished item has a hazy appearance.

Paper type and quality

Uncoated paper has a tendency to look flat and lose details. No matter how many dots per inch are printed, the end result can still look a little flat, so beware of this if you are printing high resolution work. However, we have found a great material in Fedrigoni X-Per – talk to us about getting the best results when printing on uncoated paper.

Coated stocks such as gloss and silk reproduce most screens and allow more dots to be visible.

Original file

While digital cameras are standard, some cheaper examples or mobile phones have a high pixel resolution but the image size is quite small. This means it is stretched and each time the size is doubled the DPI is halved! Make sure your camera measures up.

Wrapping things up

From a file preparation perspective, in our opinion when it comes to images DPI has the single biggest impact on print quality. Take care to deliver high resolution images in your artwork; ask your printer to scan the artwork to ensure the printing dots per inch are sufficient for the intended output.

Beware desktop software such as Word and Powerpoint as they can sabotage your efforts by downsampling the images without notifying you.

If you have any questions about DPI or any print resolution questions, please get in touch and we will be happy to help.

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