DPI and resolution explained

Resolution & DPI Explained

A question we often get asked here at Blue Horizon Printing is about DPI (dots per inch), the term is often mentioned but rarely explained, for example for us to print an image we require an image to be at least 100 DPI, this ensures that the quality of our canvas prints always meets our customers expectations. The easiest way of working out how large your image can be printed is to use our sites ordering system. However I thought it was about time I sat down and wrote a clear explanation of what exactly is meant by DPI.

Dots Per Inch usually refers to the maximum number of dots a printer can print per inch. It often is used interchangeably with PPI to describe the resolution of digital images and scanners (which produce digital images).Generally speaking the more DPI the higher quality the print will be. The term DPI usually refers to the image when it is being printed for example on canvas. In canvas printing less than 100 DPI and the image starts to show pixellation:

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With the common inkjet printer, DPI represents how many dots of ink are placed within the span of a linear inch on a printed image. Every pixel output is made up of a limited number different coloured inks, some printers have 3 colors (magenta, cyan, yellow), others have 4, and some have 6 or more. These colours must then make up all the millions of colours possible in a photograph / canvas print. To compensate for the limited number of colors, each pixel of the digital image is represented by mixing many tiny dots of ink together.

So to put this into perspective, every camera will have Megapixel ratio, for example these days most quality cameras will have at least 10 Megapixels. The word megapixel can be broken up into two words, in this case meaning 1 million, and an abbreviation for picture element. The “pix” part arises from the common abbreviation for picture. A pixel is basically a little dot that when combined with a bunch of other little dots, (one million in the case of 1 megapixel), produces what our eyes recognize as an image. Obviously it takes a lot of these little dots to produce a sizable image. https://www.bluehorizonprints.com.au/canvas-prints-sydney

When printing your image, a printer attempts to recreate it on paper by translating megapixels or image resolution to dpi (dots per inch). Dpi is the printer’s measure of printing resolution; in particular the number of individual dots of ink a printer can produce. At around 250 dpi and above the human eye has trouble seeing these individual dots of ink and the printed picture appears as one large image.

So a 1200 dpi printer uses 1200 dots of ink in every inch to make up the colours. A lower DPI would have fewer ink dots making up each pixel, which would make the colour look less clear. A higher DPI would have more ink dots for each pixel and should give more accurate colour definition (especially under close examination). In canvas printing less than 100 DPI and the image starts to show pixellation:Kidspixellate1


Calculating DPI

To calculate DPI, simply divide your images pixel dimensions by the size of the photo on canvas you’d like. (For example, if your image is 1200 pixels wide by 1600 pixels tall, and you’d like to order a 12″ by 16″ picture on canvas, your DPI would be 100. This number is ok as the dots are still pretty small (there is 100 per inch), but it would be better at 150!

At half the DPI (50DPI) the image would be twice as big however there are now only 50 dots per inch and these dots are starting to become visible.

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