Images: Print vs. Web : Understanding resolution
“But — it looked great on my monitor!”
These are words that every printer dreads hearing. Usually, it means a disappointed customer. If that disappointed customer has ever been you, with a little understanding of the differences between images on print and on screen, you can be a happy customer instead!
There are two major differences between images seen on a computer monitor, and images seen on a printed page. The first is resolution. The second is color. This time we’re going to talk about resolution.
Resolution is essentially a measure of how much information about the image is present. In traditional dot-based printing (like what you see in a magazine or newspaper) resolution is typically measured as dots per inch, or dpi. Newspapers are almost always printed at a much lower resolution than magazines. Look closely at a newspaper photograph — you can probably see the dots that go to make up the image. Now look at a magazine — you probably can’t see the dots with the naked eye. But if you pulled out a magnifying glass, you could see that they are there, but much smaller than the dots in the newspaper photo, so there are more of them in an inch. Magazine photos are at a higher dpi. Higher dpi means a sharper, clearer image.
Digital images are measured in pixels per inch, or ppi, which roughly corresponds to dpi in printing. Where the difference comes in is that computer monitor displays are very low resolution compared to print — most are only 72 ppi. So, an image that looks terrific on your monitor at 72 ppi may look blurry when printed out. For good print results, 300 ppi images are safe, but images with a ppi as low as 150 may look all right depending on how they are being printed.
If you are sending images to a print provider, find out exactly how they want the images formatted.
The images on most web sites are only 72 ppi. They don’t need to be any higher in resolution to look good on a monitor, and lower resolution equals smaller files that are faster to load, so this makes sense. But it means that you can’t grab your company’s logo from the web page and expect it to look good on your business cards.
That is, unless the image is huge on your web site, and really small on your business cards. For example, an image that is 35 inches wide at 72 ppi can be redefined to be 8.5 inches at 300 ppi. If you have an image from a web site that you would like printed out, try redefining it as a smaller image with a higher resolution, while keeping the total number of pixels the same.
Keeping the total pixel dimensions the same or smaller is very important. Attempting to stretch an image to make it larger nearly always gives poor results. This makes sense if you think about resolution as a measure of image information — on a smaller image, that information has already been discarded, so when you try to enlarge it again you are basically asking your drawing program to invent image information that doesn’t exist.
For important company images, such as your logo, the best advice is to save copies at the highest resolution possible, and know where those images are stored. That way you can always go back to the source.