Scanning and imaging techniques in platemaking
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Platform-based desktop scanning devices are now widely recognized as competing objects with traditional drum scanners, and from different perspectives, the differences have moved to indicators of productivity, image size, and maximum resolution. In addition, there are a large number of attributes that affect the decision to make a purchase.
Resolution is the standard for scanner quality. When evaluating accurately, it is important to compare the optical resolution or mechanical resolution of each device. Manufacturers typically use the largest interpolation resolution, and the added pixels actually use "creation" to increase the resolution that the sensor can achieve. The problem with other resolutions depends on the design of the device, and the maximum resolution is not supported across the entire scan area. The use of lenses reduces the effective size of larger originals to accommodate the size of the CCD array, thus also reducing the maximum scanning resolution.
The dynamic range is a measure of the logarithm of the sensitivity of the scanning sensor, especially in the dark region. Product specifications can be given in terms of Dmax or dynamic range. The starting point cannot be 0.0, so Dmax can be greater than the value of this range. In each case, the higher the number, the better the quality of the scanner. The Dmax of 3.0 is the low-end standard of professional scanners, and the Dmax of 4.0 represents the high-end equipment. This number is above the point at which the sensor reads the dark details as black.
Color depth is another indicator of scanner image quality. The final image may be output in 8 bits per color (24 bits in RGB), but the ability to obtain a larger color depth (10, 12, 14 or 16) is indicative of better quality and greater color depth. This gives the operator more opportunities to determine how the data is sampled, thus also increasing the control of the final image.
The area in which the image is scanned has a significant impact on the purchase decision. Be aware that some scanners, especially low-end scanners, use an additional file input to get a larger scanned image area, while the entire scanning area is only 8.5 x 11 inches.
The drum type photomultiplier type and the flat type CCD type have been considered as tradeoff points between scanning quality and ease of operation in the past. Advances in technology have greatly shortened this gap. However, it is generally believed that the roller type is competitive in high-resolution scanning applications, especially large format originals. In addition, off-line installation and setting, larger image areas for batch scanning, hardware-assisted processing, etc. are also reasons for the high productivity of the drum type.
RGB vs. CMYK conversion is also a factor in making purchase decisions, especially for scanners used in mass production. High-end devices typically provide instantaneous RGB to CMYK conversion through a hardware processor. Growth in online publishing and other interactive formats have increased the benefits of storing images in RGB format or in a device-independent color space than in CMYK.