SilverFast Multi-Exposure^®

What is the Dynamic Range?

The Dynamic Range of a scanner, also referred to as density range or contrast range, is a measurement for a scanner’s capability to recognize contrast levels. Contrary to reflective originals like photo transparent originals (black & white film), color negatives and slides consist of multiple film layers, which respond to light differently. Therefore, transparent originals achieve a high Dynamic Range when captured, which usually exceeds a scanner’s capabilities. As a consequence, especially in the very light and shadow image areas, image details get lost when scanning.

The Dynamic Range of each stage (capture, scanning, editing and storage) plays a crucial role in the quality of the final output. Generally, technologies with greater Dynamic Range produce better results.

How does Multi-Exposure increase the Dynamic Range?

SilverFast Multi-Exposure records an original’s maximum Dynamic Range by performing a double scan with an increased exposure time of the second scan. This procedure captures the light image area’s details in the first pass and the shadow details in the second. Afterwards an algorithm calculates the final scan, which now contains any detail, from each single scan.

The “Ansel Adams” solution for scanners

If Ansel Adams had been a software developer there is a probable chance he would have developed the SilverFast Multi-Exposure function for LaserSoft Imaging. Being the greatest master of Dynamic Range in photography, he was the first to systematically measure the sensitivity of all the equipment involved. Following his example LaserSoft Imaging researched to consider the high Dynamic Range of slides and negatives during the scan process.

Exposing an original twice with different exposure times can reduce image noise and record more image details in the light and shadow image areas at the same time. This is especially noticeable among sharp highlights and distinct textures.

Multi-Exposure was used to considerably reduce image noise in the example image on the left. In the image above Multi-Exposure managed to capture a lot more image details in the shadow areas. These differences would be especially stark when printing in large format.

For explanation: The density (density range = Dynamic Range) is specified as the decade logarithm of the light transmission’s reciprocal. That is, a Dynamic Range of 2.0, 3.0 or 4.0, respectively, means the scanner is able to implement a contrast ratio of 100:1, 1000:1 or 10,000:1, respectively. Therefore, an apparently slight Dynamic Range increase in the Canon CanoScan 9000F Mark II example from just 3.17 to 3.98 actually means that the 9000F Mark II with Multi-Exposure is capable of perceiving a contrast ratio of not just 1.479:1, but of 9.550:1. Using Multi-Exposure, the 9000F Mark II can distinguish more than 6x as many grayscales.

This kind of Dynamic Range is usually only achieved with drum scanners, which can cost up to many times the price of a flatbed or film scanner.