When the art of a skilled photographer meets the stunning craft of a professional printer amazing artwork can be created. It may seem like magic, and to some degree it is, but ultimately it comes down to a basic premise:
Quality In = Quality Out
Making sure that the digital photograph you’ve selected meets the specifications necessary to ensure a high-quality photographic print doesn't require a magic wand.
Here are 4 basic specs that you need in order to help determine image quality:
1) Digital Image Pixel Resolution (Width x Height)
2) Print Size (Width x Height)
3) Digital Image PPI (Pixels per Inch)
4) Printer’s Recommended DPI (Dots per Inch)
Once you have all of your specs it's time to do a little math. Here’s a table to help you figure everything out.
"Chicago Art Source has frequently turned to Larry when our projects require mural-scale graphics. Time and again, Larry has delivered superior image quality combined with his unbeatable eye for a unique vantage point."
Senior Project Manager
Chicago Art Source
Divide the Pixel Resolution by the Print Size to determine the number pixels per inch (PPI). Now compare the number of pixels per inch to your printer's recommended DPI (Dots per Inch). The desire is to have the PPI greater than or equal to the DPI. Bee-Bye-Bicke-Bye-Bo.
Don't panic if the PPI is less than the DPI, there's some wiggle room on the numbers. Talk to your printer to see if the difference is within their tolerance or ask them to run a test print at actual size. This is the best means to gain peace of mind.
Your printer will do most of these calculations automatically. For those of you who like to do things for yourself, here’s a step-by-step guide to help you work out the math. Enjoy.
Digital Image Pixel Resolution
Step 1: Determine the Pixel Resolution of the digital image (width and height).
In the table above pixel resolution = 4000 wide x 6000 high
Pixel Resolution measures the number of pixels on the X (width) and Y (height) axis of a digital image. The supplier of the digital image will be able to provide you with the Pixel Resolution of your selected image. In most cases, that would be TheArtAroundYou.
Note: If you decide to go with another photographer (are you crazy?), make sure to request the Pixel Resolution of the raw image prior to resizing. Some stock image suppliers will artificially enlarge an image to simulate high-resolution. We all know the opposite of Quality In = Quality Out.
Step 2: Select your Print Size (width and height in inches).
This is your responsibility, so go crazy. Just remember that size does matter. The bigger the print is the greater the need for a larger pixel resolution. This will make more sense when we get through all of the steps.
In the table above: Print Size = 20” wide x 30” high
Step 3: Calculate the PPI (Pixels per Inch).
Divide the digital image pixel resolution by the Print Size width and height respectively.
In the above example:
Width: 4,000 ÷ 20 = 200 PPI
Height: 6,000 ÷ 30 = 200 PPI
Note: Normally, the PPI for both width and height will be the same number. If not, no worries, your Print Size may require that the original image be cropped. Just calculate for the known dimension, either width or height and assume that the PPI is the same for both.
Step 4: Determine DPI (Dots per Inch)
The recommended DPI for your project will be provided by your printer and is determined by the print size, substrate, printer type, type of display and viewing distance. Your printer will figure all of this out and provide your with their recommendation.
In the above example: DPI = 150
Note: DPI represents the number of dots that a printer can generate per inch. DPI can range from as low as 72 DPI to over 2000 DPI. Usually, the more dots the higher the quality but there is a point of diminishing return. So don’t automatically assume you need the highest DPI possible. Let your printer recommend an appropriate DPI for your project.
Step 5: Compare PPI and DPI
Ultimately, we want PPI to be equal to or greater than the recommended DPI. In the above example the PPI is greater than the recommended DPI, so everything is sweet.
In the above example: PPI = 200 ≥ DPI = 150
So, what happens when your PPI is less than the DPI? The above calculation is a rough guide and there is some flexibility (plus or minus) in the ratio between PPI and DPI. For example, most printers are able to compensate for lower than desired PPI by employing color profiles that can enhance the finished print quality by blending, sharpening and smoothing individual color pixels.
Ask your printer if the PPI is adequate for your project.
Step 6: Peace of Mind
When in doubt ask for a test print at actual size. Printers are normally happy to provide a test sample of your selected image. This usually includes a small portion of the image, hopefully on the actual substrate, printed at actual size. This is the best means of determining if the original digital image will meet your expectations.