When designing digital files intended for commercial offset printing, it is essential that all of the photographs and images in your files are at least 300 dots per inch (DPI). If you have ever seen printed material that contains blurry or blocky images, it was likely caused by incorporating low-resolution images. Ensuring a high quality printed job is as simple as making sure all photos and images in your digital files are all high resolution.
All artwork design programs allow you to resize an image you are working on, but it’s important to understand why simply resizing a low-resolution image will not produce a true high-resolution image. When you resize and make a low-resolution image larger to meet the commercial printing specifications of 300DPI, all you are really doing is stretching the image. The technical term is called either resampling or interpolation. Since high-resolution images are based upon the number of pixels an image contains, resizing will not create new pixels, and will only make each pixel larger by stretching it. The only way to ensure picture-perfect high-quality printing of your photos and images is to start with a high-resolution image.