When you create a print-ready file designed for banner printing, the image needs to be 100 DPI or higher. The file also needs to be set to the size in inches of the banner you plan to order.
DPI is the number of pixels, or dots per inch, in the file. The higher the number, the better the resolution of your art will be. The better the resolution, the clearer the picture will be. This is the reason that photos found on the internet rarely work for printing banners. The standard DPI for web images is 72 DPI, and most of these images are not bigger than a 3 inch by 3 inch space. So when you blow that up the size of a banner, such as 36 inches by 36 inches, you are effectively reducing the number of pixels per inch to 6 DPI.
Even if you take the art you found online and raise the DPI to 100 using a program like Adobe Photoshop, it does not make the image look any clearer. You have to start from a high quality file to get high quality output.
Think of it this way. If you have a globe and you use a magnifying glass to look closer at it, you won’t be able to see any buildings or any better detail than what is already being seen on the globe except to make it larger. You have to have a high resolution image to begin with, there is not a way to “Res Up” low-resolution artwork.
If you absolutely have to have the art that you found online, you can redraw it using a vector program such as Adobe Illustrator. Banner printer companies can do this for you, but generally they charge an Additional Design Fee.
Next week we will be covering banner design software.