| Resolution & Scaling Resolution determines the level of detail recorded by the scanner. It's measured in dots per inch (dpi). The greater the dpi number the higher the resolution. Image quality improves with higher resolution, but only up to a certain point, after which increasing the resolution simply makes file sizes unmanageable without yielding any visible improvement to the image. A high-res image also takes longer to print. Most of the time scans of 300 dpi are more than adequate. When dealing with resolution, it's important to distinguish between optical and interpolated resolution. ¥ Optical resolution is the "native" resolution of your scanner as determined by the optics in your scanner hardware. ¥ Interpolated resolution is resolution enhanced through software. Although interpolat- ed resolution is useful for certain tasks (like scanning line art or enlarging small originals), the image produced through this type of resolution is inferior in quality and crispness to the image produced by optical resolution. Choosing the Best Resolution Setting Scanning at a higher resolution requires more time, memory, and disk space. When choosing a resolution setting, consider the type of image you're scanning and the print method or output device. An easy way to determine the best resolution for your intended output is to find out the lines per inch (lpi) capability of your output device and multiply it by 2.0 just to be on the safe side. ¥ Example: To tailor a scanned image to a typical magazine printing press that prints at 133 lines per inch, multiply 133 x 2.0. This gives you 266 dpi at final size. The optimal resolution setting for your image would be 266 dpi. Note: If you enlarge the image after scanning, the dpi will decrease proportionally, so be precise with your scaling. Lpi will vary, depending on the quality of the printing job. A newspaper uses approximately 85 lpi; magazines from 133 to 150 lpi; and fine art books may go as 200 to 300 lpi. If you're outputting images to a monitor (such as doing multimedia work or for publication on the World Wide Web, you don't need to scan the images any higher than 72 dpi, as monitors are capable of only showing images up to 72 dpi. A higher resolution image will not be any clearer on the monitor and will only create a larger file taking longer to download, etc. Remember that the higher the resolution, the larger your image file will be. For instance, an 8.5" x 11" color photograph scanned at 75 dpi takes up about 1.6 megabytes (MB). Doubling the resolution to 150 dpi will increase the file size four timesÉ to approximately 6.3 MB! Going to 300 dpi will increase file size to 26.2 MB. What you need to do then is to select the lowest possible resolution that will still give you good image quality in order to keep file sizes manageable. When to Use High Resolution High resolution is important if you're processing an image through a high-end color system that carries continuous tone data from the scanner through the final film output. This is because high resolution can improve the sharpness and clarity of the dots that make up the image. When to Use Interpolated Resolution Interpolated resolution is useful for scanning line art or enlarging small originals. (Line art is any black-and-white or single color graphic, such as a logo, ink sketch, or mechanical blueprint). ¥ For line art: Set the resolution equal to that of your output device. For instance, if you're producing line art to be printed by a 1200 dpi imagesetter, you can interpolate resolution up to 1200 dpi for superior results. This will produce smoother lines and eliminate some of the jaggedness of line art scans. ¥ For enlarging small originals: Let's assume that you scan a 1" x 2" photograph at 300 dpi, and that your maximum optical resolution is 300 dpi too. To enlarge the image to two times the original size without loss of detail, interpolate the resolution to 600 dpi. This way, the image retains clarity and sharpness even if the print size was doubled. Scaling Scaling is the process of creating larger or smaller images in your scanning software so that you need not resize the images later when you bring them into your image editing program (Photoshop, etc.). To illustrate the use of scaling, assume you scanned a 2" x 2" image at 300 dpi. To double the image size to 4" x 4" without loss of detail, increase scaling to 200% and maintain resolution at 300 dpi. This is the same as scanning the image at 600 dpi at 100% scaling and then using your image editing software to enlarge the output.
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