When you proof large graphics, the viewing distance of the final printed product needs to be taken into account. Viewing distance is probably the most misunderstood concept involved in printing large format graphics for items like signs or trade show displays. What you may not realize is that the viewing distance goes hand-in-hand with the resolution and size of an image (end product). Look at it this way:
While walking through the mall, you notice signs with photos of products and models. These images are a printed reproduction of the original. Now think about the distance between you and the images: 5 feet? 10 feet? 15 feet? Can you tell the resolution of the image (or how many dots per inch) from where you are standing? Probably not.
Or, while driving down the road a billboard featuring Michael Jordan catches your eye. It looks lifelike right? Now guesstimate the distance between you and the billboard. The distance will probably range between 500 and 2,500 feet. The average size of a billboard is 48 feet wide by 14 feet tall, and the resolution averages from two to 20 dots per inch (dpi). Imagine a one-inch by one inch square on a piece of paper. Now draw two circles side by side within the square and fill them in so that they are solid black. What you are looking at is a resolution of 2 dpi. If you were to fill a piece of paper with however many one inch squares (including the filled circles) that will fit and place it on a wall, then stand back 20 feet. Suddenly the paper starts to turn darker and the further you move back the darker the paper becomes until it appears solid black. This is the same effect that you see on a billboard.
Therefore, the closer the viewing distance, the higher the resolution needs to be. When proofing large graphics, the farther the viewing distance, the lower the resolution needs to be for your eye to create a high resolution image. Most trade show attendees view images on exhibit displays from five feet away or greater, so the 20 dpi of a billboard print would look jagged or pixelated. However, since we don’t look at banners, signs and displays up close as we would a brochure, the resolution need not be as high as for the brochure. The optimal resolution averages from 100 to 150 dpi, depending on the printer and print method.
The proof is in the proof!
Viewing a proof of large graphics should be mandatory before going to production. For large graphics, it is recommended to proof a reduced-size image of the entire file, and a finished-size swatch of any photo or area of concern. The swatch shows exactly how the print resolution will appear, while the mini version of the whole image will let you determine if any colors shifted or any elements dropped out. Note that the mini version of the whole thing may appear jagged or fuzzy because it is printed on the large format printer. As an added measure of accuracy, proofs should be printed on the actual media that will be used for the large-format graphics.
In digital printing, the goal of course is to provide the client with the best possible product, but we must also consider the product’s use, as well as the distance at which the public is viewing the product. Clients who are “in the know” can save themselves time and trouble through a better understanding of what the large-format print actually is – dots of ink. Remember: The closer you view a printed object, the higher the printing (and scanning) resolution needs to be.
The moral of the story is simple. Follow the file specifications, or “specs,” that your printer provides, and you will be pleased with the result!