Very large prints are in demand for the healthcare and corporate environments. The best prints come from the best files. How can you be sure you are getting the best quality from your digital files?
Fall forest floor, Adirondacks. Photo: © Donald J. Rommes
Iris Arts is a web-based company that sells nature photography. Most of our clients are art consultants who license our photography to make prints for placement in healthcare facilities and corporations. Although the most-requested print size is 30-36 inches wide, we are seeing more and more requests for very large prints.
For the sake of discussion, we’ll define a very large print as anything over 48 inches in any dimension.
But the requested print size can vary immensely. For instance, recent orders have been for several 60x40 inch prints, a few 150x100 inch prints, and one wall-size print 15 feet wide by 10 feet high.
Printers like to receive files at a minimum resolution of 300 pixels per inch (ppi) because, when printed, they produce very smooth tonalities
Prints from files at 150ppi resolution may not look as good on close inspection (tonal gradations not as smooth, less detail) as the one from the 300ppi file, but unless the viewer had an educated eye, and compared the two photos side-by-side, they may not be able to tell them apart, That is especially true if the photograph will be viewed at a distance, like in a corridor, or behind a desk, or even on the ceiling.
All other things being equal, camera sensor size (resolution) determines the maximum size of the print.
Over the years, digital camera technology has advanced dramatically. Sensor size has also increased.
For example, our first serious digital camera was a 5-megapixel (MP) camera. Manufactured nearly 20 years ago, and advanced for its time, the sensor size was 2400 pixels horizontally and 2100 pixels vertically. That's enough to make a 8 x 7-inch print at 300ppi.
Over the intervening 20 years, full-frame digital camera sensors increased in resolution from 16MP to 24MP to 36MP, 42MP, and 47MP. We used all of these cameras over the years. In the last year or two, 61MP and 100MP cameras became available. These are now our primary cameras.
We also use small (16-20MP), lightweight, and portable cameras for long hikes or backpacking trips, or for extended travel where weight and size are a major consideration. Many unique photos from remote locations were made with those cameras.
The 3,000 or so photographs on our website — like those of most other photographers — weren’t produced overnight. They were accumulated over years of travel using different cameras having have different native sensor resolution.
The point is, any photographer working for a decade or more probably has many excellent images made from much lower resolution cameras than they use today. Unless EXIF data is available, or the photographer provides the information, the art consultant can't know the sensor resolution of the camera that made the photograph.
Since native sensor resolution has a significant impact on the quality of very large prints, that's something an art consultant may like to consider when deciding how large to make certain prints and where to hang them.
For illustration, here's a table showing maximum print sizes at 300 and 150 ppi using the available pixels from cameras of various sensor resolutions.
Sensor Sizes and their Maximum Print Sizes
Camera Sensor Resolution Maximum Print Size (in) at 300ppi /150ppi
20MP file 18x12 / 36x24
24MP file 20x13 / 40x26
36MP file 25x16 / 50x32
45MP file 28x18 / 56x36
61MP file 32x21 / 64x21
100MP file 39x30 / 78x60
The larger the camera’s sensor size, the greater the number of available pixels, and the larger the maximum print size.
But there's more to the story. You can make a print that exceeds the maximum print size of the original file, but you must create new pixels to do so. That’s what happens when you enlarge a photo in Photoshop.
Creating new pixels is called interpolation — a process that uses sophisticated algorithms to estimate (based on its surroundings) the values of the new pixels it generates.
Different interpolation algorithms from different software companies produce somewhat different results. But regardless of the algorithm, any flaws in the original file get magnified with enlargement — artifacts and electronic noise (especially in dark areas) certainly. But the similarly-colored pixels generated by interpolation can clump together, giving a chunky or blocky look to the image.
All things being equal, the best enlargements start with carefully exposed original files that have been processed with minimal artifacts and no noise. These factors are under the photographer's control. In other words, photographic craft is still very important to the quality of the original file and its subsequent enlargement.
That craft includes careful exposure at low ISO, quality lenses, using the best RAW processor, special care in post-processing, choosing the right program for interpolation, and careful masking to restrict sharpening and noise reduction only to areas where they are needed.
Very large prints require very large files which tax computer processors and storage systems, and are a challenge to transfer electronically.
For example, the Photoshop file (16-bit) for a 60x40 inch print at 300ppi is over 1.2 Gigabytes and increases in size if further adjustments (layers) are made in Photoshop.
A 150x100 inch print requires a minimum of a 7.5 Gigabyte file at the same resolution. Those sizes are cumbersome and slow to work with, so 8-bit files at 150ppi (or lower) are often used. But even a 150x100 inch print at 150ppi requires over 1.5 Gigabytes.
As a photographer, how can you best prepare your files to make prints that size? Or do you leave it to the art consultant’s printer?
As an art consultant, how do you know the photographer’s file — whether enlarged by the photographer or your printer — will make a very large print that meets your expectations for quality?
We'll address these questions in the next segment of this blog.
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