in Images and Color
Understanding image resolution requirements for printing
To reproduce images for printing, a higher resolution is needed than what is required to reproduce the same image for on-screen uses such as email or web page marketing.
As a general rule to determine the required resolution, one would take the linescreen of the printed piece, double it, and that should be the minimum resolution of the image you provide. So, if something is printing at a 175 line screen, the target image resolution should be at least 350 pixels per inch (PPI). It is also important that your image be scaled to the same approximate physical dimensions it is used in your layout. Don't worry, you can always adjust the size a bit in your layout program. If you find yourself placing an image at 10% of its original size, this is an example where you should resize it in Photoshop.
Many of our customers provide their images at 300 PPI, which is adequate, though slightly below, the rule-of-thumb formula.
When you supply your images at a low resolution, we don't have the detail to crisply reproduce them on the printed page. To illustrate this, we started with the high-resolution nutcracker, below to the left. We then saved a version at screen resolution (72 PPI).
Above is a high-resolution
Above is a low-resolution
Above the eye detail
Above the eye detail
Depending upon the subject matter, the resolution required for print can be somewhat subjective. For example, an image with fluffy clouds may look fine at a lower resolution, while an image with great detail — such as the grille of a car — will require a higher resolution for high-quality commercial printing.
Our preflight process will identify any images which are suspect. If we flag one, you can decide the best course of action. Keep in mind that even though we catch the problem with our preflight process, this also may cause a delay while we wait for a replacement photo.
As a side note, "pixels per inch" refers to an image's resolution. Technically, "dots per inch" refers to the printed page. Regardless of whether you say "PPI" or "DPI", provide your images at a resolution of at least 300! And remember, while it's ok to scale your images in your page layout program a small amount to perfect your design, be careful that you do not overdo it! If you enlarge an image in InDesign, you are effectively lowering the resolution of the placed image inside the box. For example, if you have a 300 PPI image and you place it at 200% in InDesign, it becomes 150 PPI and will look half way between the two nutcracker examples shown.
Hope this helps! If you have any questions whatsover, please contact your sales representative.