What does the term ‘resolution’ mean to you? For some people it’s a satisfactory conclusion, drunken revellers often make one on New Year’s Eve, for others it’s a compound of spirit and tenacity.
Resolution means different things to different people. Can you see the difference in quality between the images above? This short article explains, in simple terms, the basic principles of image resolution.
Digital imaging is a complex topic and it can be confusing. We often receive digital photographs from clients that may look good on screen, but they’re less than adequate for print output. When we talk about resolution we’re referring to the pixel count, which will usually determine the optimal size and quality of a printed image.
A digital photograph has no physical dimensions, although size and resolution are intrinsically linked. The image is composed of individual pixels, which are tiny blocks of colour that make up the overall picture. The pixels are set in a grid and the term ‘image resolution’ usually refers to the number of pixels in the grid. An image with more pixels results in more detail and a better quality reproduction. Generally speaking, the higher the resolution, the sharper the image will appear on the printed page.
The resolution of a digital image is expressed in pixels per inch (PPI). It’s also commonplace to hear PPI referred to as DPI, which is technically incorrect. These two terms are closely related concepts, which merits a more in-depth explanation, but we’ll leave that out for the sake of keeping this article simple.
The optimal image resolution for commercial printing is generally about 300 PPI. Let’s suppose you have a digital photo that’s 3000 x 3000 pixels, the optimal size of the printed image will be about 10 inches (254mm) across. If we print the photo any larger then we’ll begin to see some degradation in the quality of the printed image. Once we scale the image passed the point where anymore detail can be resolved, individual pixels become visible so the image loses any sharpness of detail.
If in doubt, always supply the highest resolution file that you have. If it’s not a particularly high-res file, don’t artificially increase its size by resampling the image; that’s another article altogether.