Today’s Question: If you print an 8×10, say, whose resolution matches your printer’s maximum resolution, the print should look good. What happens if your image file has significantly higher resolution than the printer’s capability? Does the image suffer in any way? (I assume it’s not benefitted. Is it?)
Tim’s Quick Answer: If the image contains more information than the printer needs to produce the given print size, the image data will be scaled down as needed. In general this won’t produce any significant degradation in image quality, although that “extra” resolution won’t provide a benefit either.
More Detail: Different printing methods involve different requirements in terms of image data, which translates into total pixel count. In some cases there is a specific amount of information required for a given print size, such as with a photo inkjet printer. In other cases, such as with offset press printing, the requirement isn’t quite as specific, and so there is generally a range of acceptable image resolutions to use.
Ultimately, the pixel per inch (ppi) resolution you set for an image is simply shorthand of sorts to help describe the total number of pixels in the image. For example, if we assume a print size of 10 inches on the long edge, and a photo inkjet printer that renders the output at 360 pixels per inch, then we know that the image file needs to be 3,600 pixels on the long edge to achieve optimal image quality.
If we send an image that has more than 3,600 pixels on the long edge, the printer will scale down the image data accordingly. If we send an image to the printer that has fewer than 3,600 pixels on the long edge, the printer will scale down the image data accordingly.
The alternative, of course, is to scale the image data to the optimal value before printing, such as within Photoshop. In other words, with this type of workflow we need a specific amount of data for printing at a given size. Our option is to let the printer scale the image data or to do so before printing with software such as Photoshop.
When it comes to final print quality then, the real issue here is which software will do a better job of scaling the image data. In the early days of photo inkjet printing there was a significant difference. Scaling the image in Photoshop before printing generally produced a print of much higher quality than if you started with an image at the “wrong” size and let the printer software perform the scaling.
Today, however, printer software has improved to the point that the differences are quite minimal. I still personally prefer to resize my images with an advanced software tool such as Photoshop. But the difference between resizing in Photoshop and letting your printer do the resizing will generally be relatively minimal, thanks to improvements over the years in the software that controls modern printers.
Note, by the way, that different printers render the image at different resolution values. Many photo inkjet printers use a value of 360 pixels per inch, but many others use slightly lower or higher values. An increasing number of photo inkjet printers are now available that render at 720 pixels per inch, for example. It is therefore a good idea to obtain information related to your specific printer before choosing how to scale your images.