Enhancing dynamic range of a scanner
SilverFast’s Multi-Exposure generates 48 bit RAW scans that are then calculated using variable exposures. The function is similar to exposure rows, as they are known from the photography profession. With this feature, the supported scanner’s dynamic range is significantly increased while the noise of the CCD’s is effectively minimized. Hence, more details will become visible in the shadow areas of an image. Here, there is one main advantage over Multi-Sampling: Multi-Exposure reaches the same quality much faster! The slower 8x or 16x multisampling processes become completely obsolete, since a higher quality can be achieved using the Multi-Exposure feature.
Maximizing Dynamic Range in Photography - Introduction
The dynamic range of each stage (capture, scanning, editing and storage) plays a crucial role in the quality of the results. In general, technologies with greater dynamic range produce better results.
The objective of Multi-Exposure is to enhance the Dynamic Range of scans from film material since a scanner rapidly reaches its limits with single scan acquisition.
Because no substantial improvement of dynamic range can be achieved with reflective scans, Multi-Exposure works with film material only.
Todays film material, whether black&white or negative color film or slides, provides a very high dynamic range, because film manufacturers added more layers of different sensitivity.
As a matter of fact, a regular positive film, more commonly called slide film, holds a contrast range of up to 8 f-stops. A well exposed and developed negative can hold up to 12 fstops.
The Problem
The reliable capture of tone in the digital image of a photograph is influenced by many elements within the scanner.
* If the dynamic range in the captured scene exceeds the contrast range of the scanner, the details cannot be captured with that device despite the scanner’s bit-depth capabilities.
* The results are lack of information in highlights and shadows.
* The noise and grain reduce the visual quality of digital images and printouts.
The “Ansel Adams” solution of scanning - SilverFast HDR Workflow
If Ansel Adams had been a software developer there is a rather 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. But, since that did not happen, LaserSoft Imaging itself researched and developed a new dimension:
SilverFast Multi-Exposure
In order to meet or match the dynamic range of the photographs being scanned, three SilverFast products can be used in conjunction with each other:
1. SilverFast SE Plus or SilverFast Ai Studio captures the maximum dynamic range using the Multi-Exposure feature.
2. SilverFast HDR-Studio processes and optimizes the HDR-scan for output and archive.
SilverFast Multi-Exposure captures the maximum dynamic range of the original by performing multiple scans with different exposures. This is clearly different from the Multi-Sampling procedure, in which multiple scans are performed to identify and remove random noise patterns in an image. The new Multi-Exposure feature not only eliminates noise but also increases the dynamic range of the hardware.
Multiple exposures can eliminate noise and also reveal more fine image details in the hightlights and shadows. This will be most noticable in the sharp specular highlights and pronounced textures.
The Advantage
Scanning interior photographs and trying to capture subtle nuances in the highlights and shadows can be frustrating. At best, it requires time and effort and sometimes may seem impossible. This is entirely dependent on the effective dynamic range of the scanner, which is essentially the scanner’s ability to capture different tonal values in an image. So, if the software enables the hardware to capture more details in the highlights and shadows, it effectively increases the dynamic range. The graph displays the increase in dynamic range achievable using SilverFast Multi-Exposure with several different scanners.
As a reference, a dynamic range of 2.0 means the scanner is capable of reproducing a contrast ratio of 100:1, a dynamic range of 3.0 represents a contrast ratio of 1000:1. In our dynamic range tests according to ISO21550 (international standard) the Epson V700 flatbed scanner was capable of scanning a dynamic range of 3.9, which is a contrast ratio of almost 10,000:1. This means that the highlights can be 10,000 times brighter than the shadows and SilverFast Multi-Exposure will still capture details. This kind of dynamic range is usually achieved only with drumscanners, which can cost up to many times the price of a flatbed or film scanner.
Do you really need HDR Imaging and Multi-Exposure?
HDR Imaging could play a major role in the next dimension of digital imaging. In the coming decade, more and more HDR technology will arrive and change the way images are captured, processed, edited, displayed and stored. LaserSoft Imaging is proud to be a part of this process, providing an HDR imaging solution and upgrading technology that already resides on many desktops today.
Expectations are that HDR software will lead to an increase in productivity and greater expressiveness.
More information:
www.silverfast.com/show/version6-5/en.html
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