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Have Enough Resolution for Printing?
 frequently hear people tell me that they can't understand what's wrong with their printer. Their images are printing so poorly and they look just fine on-screen. Something must be wrong with the printer. Well, no. There's nothing wrong with the printer. The problem is that they haven't realized one very important factor about resolution. What you see on-screen is not necessarily what you'll see on the printed page.

The necessary amount of resolution (how well an image is "rendered") depends on a couple of different factors. Is the image simply black and white or a grayscale/color image? What is the final use of the image?

Black and white (1-bit) bitmap images are actually pretty easy to understand in this regard. A designer doesn't need any more resolution in an image than the resolution of the final printing device. This means that, if the image is being final printed on a 600dpi laser printer (a cheap flyer perhaps), the images need resolution of 600dpi at 100%. Imagesetters can output film at much higher resolutions such as 2,400dpi but the image's resolution doesn't need to be that high. Imagesetters discard all file resolution information that exceeds 1,200 dpi. That means that a 1,200dpi image will print as well as the same image at 3,600 dpi. To save on file storage, one might as well have black and white images scanned at 1,200dpi. I do and I know that I always have just the right amount of resolution for however they're printed.

Grayscale and color bitmap images (8–32-bit) are a little bit more tricky. One needs to know how the image will be output and at what halftone screen (linescreen) before scanning an image. The linescreen refers to the number lines (of dots) per inch (lpi) that will be used to simulate tones of color and gray in the printing process. A typical linescreen for a laser printer is 85lpi. A newspaper's screen is usually between 85 – 120lpi and a magazine is often between 133 and 150lpi.

A bitmap image's resolution should be twice the linescreen. That is to say that, in the case of a laser printer, an image would require 170dpi for the best appearance on a printer using 85lpi. A color magazine would require an image be 300dpi for best reproduction at 150lpi. Anything less will cause an image to deteriorate and pixelate. The amount of the deterioration depends on how much lower the resolution is than what it should be. Monitor and Web resolution (72dpi) is a far cry from printing resolution. Don't even consider using that.

Vector images, because they are created using PostScript principles, are resolution independent. Like PostScript fonts, their files are mathematical in nature and are treated as objects. A big plus for vector images.

One can find out the linescreen that the project will use by either checking the manual of the laser printer or by calling the person or company who will be printing the project. This is important information for a designer to have and the designer needs the information before scanning to avoid having to rescan images.

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