AnswersWhat's Happening?

Why are enlarged images blurry?

This is the most common question I get asked and seems to be the most difficult to explain and understand.

There are two common standards for images

  1. Screen images are 72dpi (dots or pixels per inch) and RGB (made up of Red, Green and Blue dots or pixels)
  2. Print images are 300dpi (dots or pixels per inch) and cmyk (made up of cyan, magenta, yellow and black dots or pixels)

Images can be easily converted from cmyk to RGB and visa versa. However when you come to change the size of them you can run into some difficulties.

  1. Reductions in size are usually straight forward and are sharp.
  2. Enlargements often run into problems and are blurry.

When an image is enlarged the computer has to create extra pixels/dots to fill in the space. It does this by either duplicating the same colour pixels/dots or taking the average shade of colour of the two starting pixels/dots. This substitution creates the blurred images.

The example below shows a section of 36 pixels/dots that shows what happens when you enlarge a web image by 200%.

The example below shows a section of 18 pixels/dots that shows what happens when you enlarge a web image of 72dpi to a print image of 300dpi.

As you can see by the diagrams when an image is enlarged there are a large number of pixels/dots that the computer needs to substitute. The larger an image is increased the blurrier it gets.