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As the price of computers plummets, so does the cost of peripherals. Monitors are a fraction of what they cost just a couple of years ago. The same is true of inkjet or laser printers and storage devices. One of the most dramatic changes has been the quantum improvement in flat-bed scanners. Near-drum quality is now available at a tenth of the cost you would pay two years ago. Consumer-quality scanners can be purchased for less than $100. Some of them offer quite acceptable scans for placement in casual newsletters, greeting cards and Web pages. In this column, I will offer some tips to maximize the quality of your line art scans.
Line art is black and white, without gray or color. The resulting file is referred to as monochromatic, or one color. This type of file is very compact, with just one bit per pixel, and offers high contrast. It may also be called a bitmap or raster image file. The most common format is TIF (tagged image file format), though many other formats are possible, such as BMP, WMF, PICT, etc. A line-art TIF may be placed in virtually any word processing program or layout program that will receive a graphic. The background remains white and the black pixels may be assigned a color. Transparency is not possible, so the TIF must be placed on a white background or it will be framed by a white box.
As with all scanning, the quality of the initial art is important in determining the nature of the final scan. It is possible to scan and convert color and grayscale images to bitmaps if a high degree of contrast is present. First, preview your art and select it, leaving yourself some extra room on all four sides for editing purposes. Most scan programs will allow you to set a white or a black point, or threshold, which can be helpful in minimizing cleanup. To set the white point, pick the darkest area of your white background from the preview. To set the black point, pick the lightest area which you wish to appear 100% black. If your dark areas look sufficiently black in the preview, do not set a black point. Flat-bed scanners generally darken an image as they scan because the optics are not as sensitive to the shadow details. It is only advisable to pick a black point if the art you are scanning appears quite light.
If you plan to import your scan into an image editor such as Abode PhotoShop, you will want to scan as a grayscale, rather than a bitmap. This method will allow you greater control over the final product. Set your resolution to a value that equals the final resolution of the intended output device. If you will be posting this artwork on your home page, set the resolution for 72 dpi. If you plan to print to a 300 dpi laser printer, use that setting. If you are placing the artwork in a file that will go out to a service bureau for linotronic output, contact the service bureau and find what resolution they recommend. Typically, the value will be 1200 or 2400 dpi. Keep in mind that every time you double the resolution, the file size is quadrupled. You may be constrained by the capacity of your removable media if you are preparing an electronic file.
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When your scan is complete, open the file in your image editing program. The first step in cleanup is to increase the contrast. Most image editing programs will also allow you to adjust the brightness at this time. Play with these values so that you can apply as much contrast as possible without closing up your smaller white areas. As you apply more contrast, you will brighten the art to compensate. You wish to reach a compromise that will minimize the dark areas and turn the white background bright white without introducing white pixels into the dark areas.
You must now sharpen your image. Your image editor will look for areas of high contrast and turn all pixels on one side white and all pixels on the other side black. Sometimes this is all the image editing necessary. Set the pixel threshold to zero, and the sharpening percentage near maximum. Then you may play with the radius so that you clean up as much of your white area as possible while keeping detail in the dark areas.
The next step, which all the previous steps are designed to reduce, is pixel editing. Use your marquee and other selections tools to choose large areas of stray pixels and delete them. Clean up the remainder with the eraser, brush and pencil. Use these same tools to touch up the dark areas if necessary.
Now convert your image. It is time to take your file from grayscale to bitmap. Most image editors will give you three choices; threshold, diffusion dither or pattern dither. For high contrast artwork, in which every pixel should appear white or black-a drawing made of discreet lines, for example-threshold is the best choice. For artwork in which you wish to emulate grayscales, pick dither. Diffusion dither randomizes dot placement, while pattern dither applies dots of a specific shape in a repeating pattern. If your image editor has an undo feature, you may wish to experiment with the various settings. It can be useful to save more than one final output if you wish to experiment as far as the printing stage.
The final step is to crop your art. Make your cropping marque as tight as possible to minimize file size. You should do any rotating or sizing at this time. You wish your file to be ready to place so that you do not burden your word processing or layout program with image manipulation. Finally, you must save your final artwork. In most cases, you will want to choose uncompressed TIF. Compressed files take longer to print and can even cause a printer to timeout. If you are not desperate for hard drive space, it is always advisable to avoid compression.
Happy scanning.
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