How to Enlarge With a Scanner
By Elizabeth Mott
Digitizing photos, slides and documents on a scanner enables you to use your images and other printed materials in digitally created business projects and communications. Once you scan an original, you'll see pixelation and distortion if you try to enlarge the digitally captured version beyond its scanned dimensions. When you want to use an image at larger than its actual size, or reproduce part of a document at a high magnification, you need to acquire your original at or above the size at which you want to view or print it.
Verify the optical resolution of your scanner in the documention that shipped with the scanner or on the manufacturer's website. Most scanners include two sets of resolution figures in their specifications. Optical resolution represents the maximum performance of the scanner hardware. Interpolated resolution represents a scaled-up value obtained by upsampling a scan the same way you would enlarge an image in a photo manipulation program. Only optical resolution can produce genuinely larger-than-actual-size scans.
Place photographic or document originals on your scanner, depending on whether it's a flatbed scanner set up for printed and transparent originals, or a dedicated slide and negative scanner. Set your scanning software to acquire the material at a multiple of 300 pixels per inch. To obtain a scan that is double the size of your original, increase the resolution to 600 ppi. For a 150-percent enlargement, select 450 ppi.
Preview your scan. Use the cropping tools in your software to select exactly the area you want to scan. Set your scanner to acquire the image in RGB color mode.
Instigate the scanning process. If your scanning software opens its results into an image editing program, use the program's tools to reduce the image resolution to 300 ppi without resampling the data. Your software shows the image dimensions doubling as the resolution reduces, indicated that all the data in your scan remain in the resulting image file. If your scanning software scans directly to a file on your hard drive, open the file in your image editor and resize it without resampling it.
To acquire an image both for online and for printed use, target the printed size and resolution. Create a downsampled version of the image for online use at 72 ppi.
Scanner hardware operates in RGB mode. If you need a CMYK version of an image for production use targeting a process-color printing press, create it in your image editor and save the master RGB image separately.
Scan black-and-white photos in RGB mode so you can acquire all the tones in the image. The resulting file gives you more image information to use in creating an ideal grayscale representation.
Most flatbed scanners lack the optical resolution to capture slides and negatives at a size that could create large-image versions, for reproduction purposes. If you need enlargements of 35-mm originals, look for a dedicated slide or negative scanner that features an optical resolution near to or above 3,000 ppi.
- Digital Restoration from Start to Finish, Second Edition: How to Repair Old and Damaged Photographs; Ctein
- The VueScan Bible: Everything You Need to Know for Perfect Scanning; Sascha Steinhoff
Elizabeth Mott has been a writer since 1983. Mott has extensive experience writing advertising copy for everything from kitchen appliances and financial services to education and tourism. She holds a Bachelor of Arts and Master of Arts in English from Indiana State University.