Understanding Photoshop is a biweekly column that takes an in-depth look at how digital photographs are built and manipulated. It is a college-level course in plain English for free at Photofocus. To learn more see this article.
Many purists swear that shooting film adds richness in detail and color, as well as introduces subtle nuances like film grain, which cannot be replicated with a digital camera. Additionally, many pictures that you’ll need to work with may only exist on traditional media (such as prints) or as a negative. You’ll need to use a scanner to turn these optical formats into digital formats.
Choosing a Scanner
If you work in a computer lab or other work environment, your choice in scanners may have already been made for you. However, it is still important to understand the different types of scanners that are available to consumers.
Flatbed Scanners
The most common scanner type is a flatbed scanner on which photos are loaded face down on a piece of glass. The scanner then moves a charge-coupled device (CCD) across the image to capture/digitize the image. High-quality scans can greatly increase the amount of data that is captured. So, be sure to look at high-speed scanner-to-computer connection options. For a modern computer, FireWire or USB 2 or 3 are the best options.
Be sure to pay close attention to the optical resolution of the scanner: This is the maximum size of the image before using software interpolation to enlarge it. Most users doing intermediate-level work or desktop publishing find a scanner capable of 600 to 1200 spi to be adequate. Remember, samples per inch can translate fairly well into pixels per inch. It is a good idea to have more pixels to start with, and then reduce the size of the image for delivery.
Common ppi Requirements for Final Files
- Onscreen (web/slides) 72–96 ppi
- Laser printing 150–250 ppi
- Newsprint 120–170 ppi
- Offset printing 250–300 ppi
- High-quality offset printing 300–600 ppi
Film/Slide Scanners
Specialized scanners load in slides or film negatives. These scanners use a tray to hold the material, and then a motor pulls the tray slowly across an optical sensor. This process is relatively slow due to the resolution needed. The scanner must capture a lot of data from a very small surface area to produce a usable image. These scanners are slightly more expensive than flatbed scanners but are essential if you frequently work with slides or negatives.
Need a Scanner?
Many all-in-one printers combine a printer and scanner, essentially creating a fax machine and photocopier in the process. Be sure to check if your printer offers scanning software to load your traditional photos. You can also rent scanners at many local photocopy shops.
Drum Scanners
When top image quality is a must, pros turn to drum scanners. These units are very expensive (starting at $5,000 and increase significantly). This is the oldest scanning technology. It calls for the image to be mounted on a drum. The drum is then rotated in front of a photomultiplier tube. The tube is much more sensitive than the CCDs used in flatbed scanners. Drum scanners’ primary advantage is resolution, and they should be used when you need to significantly enlarge a scanned image (such as museum archival pieces or for magazine output). Because the machines are expensive and very complex (as well as potentially destructive), users will often send images to a service bureau for drum scanning.
A drum scanner is a highly specialized piece of equipment. These machines are very expensive and are usually found only in high-end, service bureau facilities.
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Rich Harrington is a photo and video pro based in Washington, DC. He is also the publisher of Photofocus and host of the podcast. Rich has written many books through the years and is an active trainer on lynda.com. To see more of Rich’s articles, click here.
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