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Digital Cameras
Scientific imaging uses two different types of sensors in digital cameras, CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor). CCDs are used extensively in microscopy and astronomy, as well as in many other types of image acquisition devices. CMOS is the "up and coming" technology, mainly due to lower costs of manufacture, however, CMOS currently tends to have higher levels of electronic noise than CCD (this may change as the technology improves).
Several introductory resources with information about Digital Cameras :
What's inside a Digital Camera? (Kodak Digital Learning Center)
Digital Cameras (The PC Technology Guide)
CCD History (NASA & Lucent Technologies)
More technical information about CCD and CMOS sensors:
CMOS advantages (Micron Technologies)
CCD Encyclopedia (Roper Scientific)
CCD University (Apogee Instruments Inc)
Information about consumer digital cameras (unfortunately there do not appear to be "buyers guides" for scientific grade cameras, possibly due to the low volume that they represent):
Megapixel.net (a monthly digital camera web magazine)
Digital Photography Review
Imaging Resource
Digital Camera reviews (ZDNet)
CNET : Hardware: Cameras
Scanners
Desktop and film scanners are CCD imagers that use either reflected or transmitted light to create images of paper or film. Scanners are often advertised based on their maximum optical resolution and bit-depth. While these values can be important, its also worthwhile to consider how the image is to be used before creating an enormous file (an 8x10 color image scanned at 1200 dpi with 36 bit color would create a file in excess of 500 MB).
Resources and tips for scanner users:
Sullivan's Scanning Tips On-Line (Haywood & Sullivan Design)
A few scanning tips (Wayne Fulton, Scantips.com)
Scanning (About.com)
Scanners (The PC Technology Guide)
Using a scanner on images from magazines & journals occasionally causes an artifact called moiré (from the French, meaning "wavy"). This phenomenon is due to inadequate sampling (by the scanner) of the halftone pattern used to print most periodicals. Here are some specific tips on how to deal with moiré:
(NOTE: scanning of published materials assumes that you have permission from the publisher to use copyrighted materials or are operating under the "fair use" doctrine) |
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Information about scanner hardware:
CNET: Hardware: Scanners
Scanner Reviews (ZDNet)
Imaging Resource
Film Scanner Reviews (Tony Sleep Photography, UK)
Printers
Printing usually involves the process of computer software transforming an on-screen RGB image into a hardcopy CYMK image. Because these two color spaces are not identical (CYMK is smaller), there are potential problems.
Most printers are "bilevel", they produce a pattern of individual dye "dots" of a single intensity. Bilevel printers are incapable of creating shades of colors, so to create the illusion of color, they map the dots into a grid called a dithering cell (also referred to as halftoning). A 5x5 cell of "dots" can dither 26 shades of an individual color and with three colors can create the illusion of 17,576 colors. Multilevel, or contone, printers can print more than one shade per dot, so they need smaller dithering cells to represent a specific color. Continuous tone printers can print multiple shades of each dye color and add them together on the paper to create millions of colors per dot. (source: PC Magazine 10/27/97). Bilevel printers would include inkjets and laser printers (although the newer printers may be multilevel) and continuous tone printers would include dye-sublimation and the FUJI pictrography printers.
The use of dithering creates a problem in determining the true number of pixels/inch that a printer can produce. Printers are typically advertised based on their resolution in dots/inch. Continuous tone printers can map each pixel in an image to a single dot on a page, so their resolution is the same as the dpi of the printer. However, bilevel and multilevel printers must use dithering and this effectively lowers the number of pixels that the printer can reproduce per inch. For example: the HP4500 color laserjet in our department is a 600 dpi printer, however, since this printer must dither to reproduce colors, the actual resolution for color graphics is 155 lpi (lines per inch, per Hewlett-Packard). LPI is the effective resolution (pixels/inch) of any printer that uses dithering to print digital images.
NOTE: because the LPI value is dependent on the maximum DPI of the printer and the type of halftone screen & printing technology used, check with the printer manufacturer to determine the LPI for a given model (a useful table for approximation).
Excellent introductory resources about printing:
Output (Kodak - Digital Imaging Fundamentals)
Printing (Kodak - Digital Color Theory)
Image Resolution (Kodak - Printing Digital Images)
Other printing resources:
Resolution: DPI, SPI, LPI and PPI (About.com)
Laser Printers, Inkjet Printers & Other Printers (The PC Technology Guide)
Information about printer hardware (NOTE: hardware reviews from business-oriented publications tend to look more favorably on less expensive printing technologies and/or faster printers for digital images. In the field of scientific imaging it is sometimes necessary to choose the more expensive and slower technologies to achieve the image quality needed for publication and/or presentation.)
Printer Reviews (ZDNet)
CNET: Hardware: Printers
Printer Reviews (CreativePro)
