Here is a quick guide that explains how we measure image resolution and what is required for both print and on-line/screen images.
Image resolutionIn the context of editing photos, resolution is a measurement of the output quality of an image. It’s important to explain how image resolution is measured. Within the industry there are several different units that are used to measure this but we will focus on the most common, DPI (dots per inch) and PPI (pixels per inch).DPI (dots per inch): This specifically refers to how many dots of ink will print per inch. The higher the number, the clearer the image will be.In general, for all printed material the required resolution is 300dpi. The exception to this is for large format printing such as Billboards where the lowest acceptable resolution is 72dpi. It is acceptable in this case as the images will be viewed from afar so the dots will not be visible to the naked eye.If you are taking images yourself, below is a quick reference list to help you recognise if an image you have is suitable for print:
- 5 Mega Pixels = 2592 x 1944 pixelsGreat Quality: 25.5 x 33cm
(10 x 13 inches)
- Good Quality: 33 x48cm (13 x 19 inches)4 Mega Pixels = 2272 x 1704 pixels
- Great Quality: 23 x 30.5cm (9 x 12 inches)
- Good Quality: 30.5 x 40.5cm (12 x 16 inches)3 Mega Pixels = 2048 x 1536 pixels
- Great Quality: 20 x 25.5cm (8 x 10 inches)
- Good Quality: 25.5 x 33cm (10 x 13 inches)2 Mega Pixels = 1600 x 1200 pixels
- Great Quality: 12.5 x 17.5cm (5 x 7 inches)
- Good Quality: 20 x 25.5cm (8 x 10 inches)PPI (pixels per inch) – This term is used when referring to online and screen resolutions.
For web imagery images must be at 72ppi. This allows them to be viewed clearly and also helps to keep the file size of the page down which in turn enables the page to load faster.This is why typically images from the internet are not suitable to print from.It is important to remember that the resolution of an image can always be reduced but it can’t be increased. When you try to enlarge a picture with a low resolution, you are asking for pixels to be added that don’t exist; the image will get blurrier.