In printing terminology, resolution is the number of pixels (or dots) that make up a computer generated image. This is usually expressed as the number of pixels across by the number of pixels down, for example 3000x2000pixels. Sometimes, we see the same concept but expressed as the total number of pixels that make up the image, so the example above (3000×2000) would be a 6 million pixels image or a 6 megapixel image.
When we look at an image on a computer screen, this image is rendered with a fixed number of pixels per square inch of monitor surface, and this is called dpi or dots per inch (sometimes called ppi or pixels per inch). A standard computer monitor has the capacity to render 72 pixels per square inch (retina screens renders double that).
In printing, however, the printer’s capacity to render images has a much higher density, as much as 300dpi for high end lithographic printing. What this means is that if we print an image with only 72dpi using a machine that requires 300dpi, the image will appear as of low quality and showing the pixels prominently. To use an analogy, it is like painting a wall, one coat will look unfinished, two will look denser, and a third coat will make the colour on the wall solid and evenly distributed, of a professional finish.
So how can I ensure that the image I choose to send to the printers is ‘dense’ enough or has the right resolution? To use the painting analogy, you get more paint to be able to give the wall three coats… and for the images, you get enough pixels across and down to ‘fit’ more of them in each square inch, and therefore increase the pixel ‘density’ or resolution. This would be approximately 3 times more pixels! By reducing the size of an image approximately 3 times we bring a 72dpi image to an optimum printing resolution of 300dpi.
Still confused? Let me make it a lot simpler using a little trick. Divide the number of pixels across and down by 10 and this will give you approximately the size in millimeters at which you can safely print that image…
For example, the image above was 3000x2000pixels, and when you look at it on your computer screen will appear to be larger than the monitor. If we divide the pixels by 10, we get 300x200mm, which is approximately the dimensions of an A4 sheet of paper (210x297mm). In other words, a 3000x2000pixels image would be ideal for high resolution printing (lithographic printing) up to approximately A4 in size.
This is a very simplistic approach to the concept resolution. Some types of printing such as digital and wide format do not require the full 300dpi. For example many digital machines would render a good definition print from just 150dpi. This would be the same as dividing the number of pixels by 20 to get the optimum millimeters. Just make sure you check with your printer about the quality of the images if you are in any doubt.
At Print Bureau, we have an expert team of project manager and designers that can advise you on how to make the most out of your images or how acquire high resolution Royalty Free images for your publications to enhance the visual impact of these. Contact us and we will be delighted to help.