Image Resolution (DPI) | Does it matter?

YES it does – it is critical!
Images on screen are made up of individual dots or ‘Pixels’. Each pixel is a single colour which when used small enough, and close enough to hundreds of other pixels will fool the eye into seeing an image.  If you take a close look at magazine images you will see that they are comprised of lots of coloured dots, which although aren’t technically ‘Pixels’ they are performing the same job. The resolution of an image is simply the amount of pixels for a given area, which is normally given in ‘Dots Per Inch’ or ‘DPI’ (‘dots’ simply means ‘Pixels’).  Magazines are generally printed with images at 300dpi. Newspapers are printed at a lower resolution with images typically 200dpi or less, which is why when you look at newspaper images the dots are more noticeable – there are less of them per square inch. So in general resolution is an indication of the detail an image contains and is a good indication of the ‘quality’ of the file. However the lighting, sharpness, colour-balance and the general expertise of the photographer will all dictate the actual quality of the image. Now lets take a look at monitor or screen resolutions…

Computer monitors come in a wide range of screen resolutions which means that an image will be displayed in various different sizes dependent on the monitor settings. However as a simplified ‘rule of thumb’ images for screen-only work (i.e websites and emails) are required to be around 72dpi. This is accepted as the ‘norm’ in terms of screen resolution and minimises file sizes whilst maintaining the quality of the image. Because this resolution is much lower than that of print, an image which looks perfectly fine on screen will not look as good when printed. Lets look at an example to see why: Imagine an image which is 720 pixels wide by 720 pixels deep. On a 72dpi screen this image will be 10 inches square, however at 300dpi it will be less than 2.5 inches square. At this smaller size the image will look just as good in print as it did on screen, but if you want it to be 10 inches square when printed then you’ll have to enlarge it. This can only mean one thing, you are going to need more dots!

Just make it bigger…
Image manipulation software such as Photoshop has very complicated mathematical algorithms which can ‘interpolate’ the image, but in essence it is still just adding in pixels of similar colours around all the existing ones in order to create the illusion of a larger resolution image. Although the best interpolation software is much better than simply ‘blowing-up’ the image, there are limits to how good the final image will end up being. In general the larger the resolution and size of the original image, the more it can be enlarged before pixellation starts to become noticeable. This is because there is more information in the image – i.e  ‘dots’ – so there is more information to work with. However, any image that is enlarged too much will start to look very blurry or pixelated

  1. Images intended for print should be a minimum of 300dpi at the physical size you want to print them. If you do not have software that gives you this information, then Pixooma will be able to advise you.
  2. File size is not necessarily a good indicator of the actual image size, especially with JPEGs as they are a compressed file format.
  3. As a general guide you should expect that any image you view on screen will be approximately 1/4 the size when printed professionally.
  4. If you have access to software that can do so, DON’T simply enlarge an image or change its resolution. This will simply add pixels to give an approximation of what a higher resolution inage would look like. It is better to leave images as they are and get Pixooma to advise on whether the image can or should be enlarged.
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