What is DPI?

At Ortery Technologies, we have come across many customers who misunderstand DPI. Specifically, they get it mixed up with image resolution and how it is related to printing a digital image. Today we would like to shed some light on this and hopefully make the relationships between these terms clearer.

DPI stands for ‘dots per inch’. This terminology is from the time of dot matrix printers and literally means how many dots will be placed on the paper per inch. So, essentially it is print resolution.

Digital images use pixels to measure resolution. Image resolution is figuratively equal to pixel width multiplied by pixel height and expressed in MegaPixels (MP). For example a 12MP camera with a 4:3 sensor ratio would be able to produce pictures that are 4000 x 3000 in size. (4000×3000= 12,000,000 pixels = 12 Megapixels).

A visual representation of DPI in photography

 

To print a 4″ x 4″ picture at 300dpi, you will need an image that is at least 1200 x 1200 (or 1.44 Megapixels). In this case, PPI and DPI are the same. Note however that PPI and DPI are meaningless unless there is an intended print size. In this case 4″ x 4″.

Monitors and the Internet typically display images at 72 or 96 PPI. So, if you wanted to show a 4″ x 4″ image at 72 PPI on your website, then you would need an image that was at least 288 (72 x 4) x 288. What we can see here is that you need a lot fewer pixels to display images online than you do with print. So if you are taking pictures for the web, you may not need a 24 MegaPixel camera. It is essentially way, way overkill.

DPI-1

For print, however, it is nice to have a lot of megapixels to work with. Here is a chart from DigitalPhotographyLive.com that shows what MegaPixel value corresponds to printing at three different dpi (print resolutions) – Excellent, Good and Poor.

megapixel-vs-print-size-465x263

At Ortery Technologies, we have come across so many of our clients asking how DPI applies to their website, print, and other marketing media. We always refer them to the simple definition and work with them to see what would be the best output for their product photography needs. Ortery Technologies solutions are capable of producing professional quality image and video files for all media outputs.

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