Sizing Images for Printing, Display or Projection

Jul 31, 2017  By William Royce
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To get the best out of every image, photographers should understand how to correctly size image files, whether they are from a digital camera or a scanned image from film. Most importantly, you don’t want to create an image file that is too small. A good Leica image deserves the highest quality you can reasonably obtain from it, regardless of how you show it. This article explains how image sizing is done, whether you are creating a print, displaying it on a computer, or projecting the image to a room full of people. I will also discuss an interesting fact: both Lightroom and Photoshop are capable of “up-sampling” images which, in their original state, don’t have enough pixels to provide a satisfactory result. This means here are ways to create more pixels to meet your needs.

PRINTS
It has been said that prints are the ultimate display medium for photographs. For acceptable quality, prints should be at least 300ppi (pixels per inch), in both the vertical and horizontal direction. This means you need a digital image file that provides enough pixels to achieve this count. The good news: recent Leica cameras (and of course other brands)  produce images with pixel counts more than adequate for very large prints. Even the M8, at 10.2 MP, can produce excellent images that are quite large. A table of pixel dimensions, with a corresponding 300ppi print size, follows:

It is also worthy of mention that a modestly priced flatbed scanner can produce scans of 35mm film at about 2000 ppi, which will yield an image file that is about 3000 x 2000 pixels in size with reasonable quality. Flatbed scanner manufacturers may claim much higher resolution but most will only produce larger files that do not increase in true resolution above about 2000 dpi. Some high-resolution scanners may produce better results, including drum scanners, but can be very expensive.

To determine the required pixel count (image size), you need to consider the size of the print. For example, a 12″x18″ print, at 300ppi, needs pixel dimensions of 5400 x 3600. In Lightroom, the pixel count is determined by the export or print process. If you are ordering a print from a printing service, you will need to export an image file that has sufficient pixels to yield ahigh-qualityy print. During export, set the Image Sizing to the desired inch dimensions and set the resolution to 300ppi or better. The following illustrates this recommendation. Once the Export is complete, the resulting JPEG in this case will be 5400 x 3600 pixels. (figure 1)

In Lightroom, if you are printing directly from the image (without exporting), you need to first select the image you wish to print, select the Print function and specify the layout and size of the final print, including the paper size. Under the Print Job tab, set the print resolution to 300ppi or higher. (figure 2)

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