Scanning
The goal in scanning is to capture all of the information that will be needed for reproduction.
- Information not captured in the scan can never be replaced.
- Image processing techniques can improve, enhance or correct a degraded image if the mechanism of degradation is known.
- A scan should capture all the detail of the original that can be reproduced, while keeping file sizes manageable.
- The resolution of the printing device should be considered when choosing the scanning resolution.
- The first color scanners were analog rather than digital.
- All scanners contain elements similar to the human visual experience.
- Light sensitive capture elements (photons are absorbed and electrons are emitted.).
- An optical system for focusing the image.
- Filters (usually RGB)
- Transport system to either move the original or the scanning apparatus.
- Software (Controlling and processing).
Drum Scanners - Usually use photomultiplier tubes (PMT), one each for RGB. Unsharp masking and color separations are often performed on-line. A PMT consists of a photocell inside a vacuum tube. PMTs can detect densities up to 3.5 to 4. On a digital scanner adjustments for different images can be made from within programs such as Photoshop.