CREATING A DIGITAL FILE: Details

The following section contains guidelines for creating digital files (cover or text) that you send to Webcom. It covers preflighting, image and font handling, gradients, tints and other elements that go into the creation of your electronic document. By following these helpful hints, you can create digital files that will work smoothly with Webcom’s all-digital workflow. This way, you’ll get your books and other book products to market faster!

SCANNING YOUR IMAGES

Halftones
One of the most common problems encountered in digital prepress is that the images supplied to Webcom are at too low a resolution. The final resolution of scanned halftone images should generally be 300 dpi at 100% of the reproduction size. If you are in doubt about the resolution at which to scan your original image, calculate the scanning resolution using the following equation:

2 x line ruling (in lpi) x reproduction factor

The line ruling used for covers is 150 lpi and for text pages is usually 120 lpi.

To find the reproduction factor, divide the final size by the original size.

For example, you have a 4" x 5" original which is to be reproduced on a cover as an 8" x 10", the reproduction factor (using the width of the original) is:

8" ÷ 4" = 2"

In this example, the image is for the cover, so the line ruling is 150 lpi. Therefore, you would need to scan the original at:

2 x 150 lpi x 2 = 600 dpi

This resolution amount may seem high, but remember, your 4" x 5" is being blown up 200%.

If you had an 8" x 10" that was only going to be reproduced as a 2" x 2.5", then the reproduction factor would be:

2" ÷ 8" = 0.25"

You would need to scan the original at:

2 x 150 x 0.25 = 75 dpi

This resolution amount may seem low, but remember, your 8" x 10" is being reduced to 25%.

This is generally a good way to calculate your scanning resolution, except that sometimes you have no way of knowing what the final dimensions of the image will be. If this is the case, scanning at a slightly higher resolution will allow you to enlarge the image slightly without sacrificing quality. Remember, though, if you have a 300 dpi image that you enlarge to 200%, it is now only a 150 dpi image!

Line Art
While the scanning resolution equations above are helpful for halftone scans such as pictures of people, line art (logos, type) is treated somewhat differently. For line art, a higher resolution is required. They should also be scanned as Monochrome and not as Grayscale.

You may use the following chart as a quick reference for minimum and ideal image resolution. The exceptions to all of these rules are screen captures, which are 72 or 96 dpi and should remain at that resolution.

Dot Gain Considerations
You may be accustomed to scanning your images while keeping dot gain on press in mind. With Webcom’s Computer-to-Plate system, this is no longer necessary. Our platesetters have calibration sets built in that will automatically compensate for dot gain as they output the plates.

Scans supplied to Webcom should not compensate for dot gain or they will look washed out due to the combined effect of the two compensations. Instead, scan your halftones with a 5% highlight dot and a 95% shadow dot. For grayscale images, the highlight is the lightest area carrying detail and the shadow is the darkest area carrying detail. For colour images, the highlight is the lightest neutral area carrying detail and the shadow is the darkest neutral area carrying detail.

The size of the midtone dot will depend on the nature of your original. If you have a high-key original (i.e. a polar bear in a snowstorm) you will want a larger midtone dot in order to provide better detail in the highlights. If you have a low-key original (i.e. a black cat in a coal bin) you will want a smaller midtone dot in order to provide better detail in the shadows.

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