A common issue in photography is file size and resolution. Many times people will get an image for a project or for print and find that image is not suitable for the particular application because the file is either too large or too small. Different output applications require different resolutions. Knowing how photo scanners work will give the consumer a better idea of what type of scanner is best suited to their needs.
Analog to Digital
Scanners convert analog photos into digital files. Flatbed photo scanners use a charge-coupled device (CCD) sensor. Light is passed across a photograph, the CCD reads the information and converts light into digital information in the form of pixels that make up an image on the computer.
Resolution and Dynamic Range
- Resolution or ppi (pixels per inch) is the number of pixels the scanner acquires during the scan. Pixels are the digital information or interpretation of the film image. A large resolution allows an image to be enlarged and still maintain a good print quality in the image. Flatbed scanners scan one row at a time and continue down the photo with carriage moves. A 1200x2400 dpi (dots per inch) scanner reads 1200 color samples per inch. The first number is the optical resolution of the CCD and the rating of the scanner, i.e. 1200 dpi scanner. The 1200 dpi is the amount the CCD scans. The larger number is the possible positioning of the carriage stepping motor. Stepping motors move in precise steps, at each pulse the motor moves only 1/2400 inch vertical steps. The motor rating of 2400 does not add to the optical rating.
- Bit depth is also important for overall image quality. An 8-bit scanner reproduces 256 colors and a 24-bit scanner reproduces 17 million colors and so on up the range of numbers.
- Dynamic range is the amount of recordable colors and shades from pure white to black. A high dynamic range means less noise in an image and greater highlight and shadow detail. The higher the dynamic range of the scanner the more pixels a scanner can acquire.
Scanner Software
Many scanners come with some sort of interpolation software that lets the user make minor adjustments before the scan. A preview window will open where the scan parameters are set and any edits can be made here. Since CCD scanners have some trouble reading some highlight and shadow detail, it is best to do a raw scan and make edits in a dedicated software-editing program.
Physical Components
Flatbed scanners with CCD sensors have improved in quality. The basic assembly is a light box, a glass surface to lay the copy onto, a carriage with a CCD sensor that moves under the glass to scan the image and a cover (or lid). These scanners use high-luminance white LED lamps as their light source. These lamps do not need any warm up time, they use less power to operate and do not contain any mercury so they are environmentally friendly. In addition, they are user friendly, just put the photo on the glass, close the lid and set the scan.
Caroline Thompson - Caroline Thompson has been a professional photojournalist since 1999. She combines writing and photography in her stories. ...
