"How To" Guides > Printing Images
Printing Quality Photo and Document Digital Images
The single most important factor in producing quality prints from digital images is deciding on the pixel per inch (PPI) resolution to reflect in prints. Rules of Thumb for pixels per inch are recommended in this article by consolidating thoughts from many sources.
Quality Printing Considerations
Affordable, easy to use, and very capable consumer printers now make it possible for non-professionals to produce their own high quality prints of digital photo and document images.
On the other hand, many local and online printing services offer reasonable pricing, consistent high quality, and a broad range of print sizes and image products. With the easy ability to upload/transfer digital images to these printers, it often makes sound sense for families and local historical societies to turn to these professionals for many of their printing needs, particularly for photo realistic image enlargements.
Regardless of how much printing you may have done professionally, it is useful to understand printing processes and terminology. This will make you a better printer and/or consumer of printing services.
Rules of Thumb for Photo Print Resolution
Cropping and aspect ratio considerations aside, digital image file pixel dimensions for height and width are spread over inches of paper in the printing process. A given number of pixels spread over a 4" x 6" piece of paper will be reflected as more pixels per inch than the same number of pixels spread over a piece of paper that measures 8" x 10". It is this density of pixels in the print that is the greatest impact on photo print quality.
Opinions vary as to what level of pixel density or resolution is needed to attain satisfactory print results. It is generally agreed that the eye is not capable of discerning differences beyond 300 pixels per inch. The following defined ranges are an attempt to consolidate the thoughts and recommendations of many.
300 PPI / Professional Photo Quality - The photo print resolution quality targeted by professionals. There is broad agreement that one does not obtain a print quality advantage beyond 300 PPI.
240 to 300 PPI / High Photo Quality - Many agree that few people can discern a meaningful difference between 240 PPI and 300 PPI. Therefore, for most non-professional image uses, this level of resolution should not compromise results.
200 to 240 PPI / High Quality - Among resolution recommendations of professional printers, this range is often described as very good quality. (You may recall our recommendation to perform archival scans at 600 PPI. This suggests that the 600 PPI scan can be tripled in print size and still maintain a print resolution of 200 PPI.)
150 to 200 PPI / Good Quality (Photo Realistic) - In this range, you may want to test prints at various sizes before committing resources to a major project. Based on minimum resolution standards set by major online printers, you are still likely to be satisfied with print resolution in this range.
100 to 150 PPI / Acceptable Quality - Results in this range will vary based on the nature of the image, the size of the print, and the intended purpose of the print. It is possible that results are still satisfactory.
Confusion Between Pixels Per Inch (PPI) and Dots Per Inch (DPI)
Frequent reference to dots per inch (DPI) often confuses the discussion of print resolution. DPI is simply how many dots of ink a printer can lay down on an inch of paper. It is generally agreed that when a printer is capable of DPI in the range of 600 for text to 1200 for photo realistic images, this is sufficient for most non-professional printing needs. With modern printing technology, it is generally agreed that print quality is not improved noticeably beyond this, and today's moderate priced printers exceed these DPI levels.
In describing and recommending rules of thumb for printer image resolutions, our primary focus is placed on pixels available in a digital image file and how you choose to reflect them as pixels per inch (PPI) in the printed image.
