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PGY 4440C PHOTO COMPUTER IMAGING
Scan Resolution and Scaling
Resolution determines the level of detail recorded by the scanner, and is 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 resolution simply makes file sizes unmanageable without yielding any visible improvement to the image. There are two types of 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, and is
useful for certain tasks like scanning line art or enlarging small originals.
Choosing the best setting
When choosing a resolution setting, consider the type of image you're
scanning and your printing method. 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 1.5 to 2.0.
Example: To tailor a scanned image to a typical magazine printing press that prints at 133 lines per inch, multiply 133 x 1.5 or 2.0. This gives 199.5 or 266. The optimal resolution setting for your image would then be 200 dpi to 266 dpi (depending on how high the output quality will be). Lpi will vary, depending on the quality of the printing job. A newspaper uses approximately 85 lpi; magazines from 133 to 150; and fine art books may go as high as 200 to 300 lpi.
If you're outputting images to a monitor (such as doing multimedia work), you don't need to scan images 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 simply create larger files.
Remember that the higher the resolution, the larger your image file will be and the longer it'll take to print. An 8.5" x 11" color photograph scanned at 75 dpi takes up about 1.6 megabytes (MB). Doubling resolution to 150 dpi will increase the file size four times - to approximately 6.3MB! Going to 300 dpi will increase file size to 26.2MB.
What you need to do is to select the lowest possible resolution that still gives you good image quality to keep file sizes manageable.
Using high or interpolated resolution
High resolution is important if you are 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.
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, when producing line art to be printed by a 1200-dpi imagesetter, you can interpolate resolution to up to 1200 dpi for superior results. This will produce smoother lines and eliminate some of the jaggedness characteristic of line art scans.
For enlarging small originals: Assume that you are scanning a 1" x 2" photograph at 300 dpi, and that your maximum optical resolution is 300 dpi as well. 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 they are delivered
to your image-editing program. Scaling has an inverse relation to resolution:
The lower the resolution, the larger the image can be scaled. At the highest
resolution, images can only be scaled smaller.
To illustrate the use of scaling: Assume you scanned a 2" x 2" image at 300 dpi. To double 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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