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.

Last time, we talked about resolution as it relates to print vs. web image reproduction. This time, we’re going to talk about color world.

Your computer monitor creates color using light, like a television screen, using the RGB or red, green and blue model.

The print world creates color using pigment. Full color images are commonly rendered using the CMYK or cyan, magenta, yellow and black model, but some high-end print shops use the Pantone Hexachrome model which adds orange and green to the color mix. Items might also be printed using spot colors (such as those defined in the Pantone matching system), metallic or iridescent inks, or varnishes that give particular visual effects. In addition, the color and reflective quality of the paper affects how a printed image looks.

What this means, simply, is that the colors in your document do not look the same on the screen as they do on the printed page.

In fact, the colors in your document might not even look the same from one monitor to the next – equipment age and manufacturing differences can cause a great deal of color variation in individual monitors.

Similarly, if you print your document on your color office printer (which probably uses the CMYK model), you may not get the same results on a different office printer, or with a professional printer.

If your color requirements are not strict, you may never run into a problem. The sky looks blue on your monitor – it looks blue on your printout – no problem! But there are a couple of common pitfalls when moving an image from the monitor where you do your layout to the printed page.

1. Dot Gain
“Dot gain” refers to the tendency of printed dots to spread as the ink soaks into the paper. This is particularly noticeable on newsprint, which is uncoated and very absorbent (as anyone with a puppy can attest!). If you are preparing something to be printed on newsprint – such as an ad – for the image to look right on the paper, it will probably have to look too light on your monitor.

2. Luminosity
Images on your monitor are luminous – lit up. Images on paper are not. This can make printed images look too flat and dark if you are expecting them to look like the image on your monitor. Again, making the image appear too light on the monitor can give better results on the printed image. Using a coated paper stock or a varnish can increase the apparent luminosity of a printed image. Sometimes shifting the color mix toward yellow or green can make the image seem more luminous.

When going from screen to print, if you are having the image professionally printed, your printer may have some good ideas about how to improve your results.

When going from print to screen — for example, if you want your website to look like your business card — you will want to talk to your web designer about how to get the best results.