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.

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 7,000:1. This means that the highlights can be 7,000 times brighter than the shadows and SilverFast Multi-Exposure will still capture details. These two graphs illustrate the increase more drastically in luminance values.

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.

For best possible results please assure that the image is not moving during the multiple scan passes: Either use a film template or fix the image with tape. This is needed to prevent the film from moving due to the vibrations and movements of the scan, otherwise additional scan passes would scan different crops.

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. SilverFast 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.

Make sure that your scanner supports Multi-Exposure.

Multiple reflective or transparent images can now be selected, scanned and optimized automatically using the new Automatic Frame Detection.

The workflow is very simple:

1. Perform a prescan or preview the image.
   SilverFast will initially display one large frame for the entire preview window.
2. Select AutoFrame button to activate the auto frame detection.
3. SilverFast now generates individual frames for each image.
4. The auto adjust will then optimize all images automatically.
5. Additional corrections such as sharpening, image size or resolution can be done individually.
6. All images will be corrected by a single scan. The batch function may also be used for this purpose.

Example: automatic frame detection in SilverFast Ai

Prescan without (left) and with (right) automatic frame detection

The automatic frame is available for all SilverFast 6.5 versions and is best suited to identify images which are positioned on the flatbed without an image holder.

In those cases where an image holder is required, the recommendation would be to generate an according template and save the positioned frames, "General / Save Frame".

The AutoFrame Alignment was developed and designed to offer the user an extremely efficient, yet convenient scanning experience. When positioning multiple images on the scanner, AutoFrame Alignment and the frame detection will not only "find" and frame the originals, it will align them in a rectangular order. Pictures will automatically be rotated for straight edge alignment. Manually cropping and aligning images in another editing application is no longer necessary.

SilverFast's intelligent detection and alignment algorithms perform these actions with a simple selection. Image frames can also be arbitrarily rotated for further fine tuning.

With version 6.5 SilverFast SE, SE Plus, DC SE and DC VLT include the new SilverFast Basic mode.

SilverFast Basic provides a simplified user interface to give beginners an easy start in SilverFast. In basic mode, users become familiar with the essential features of the imaging software while being presented only with minimum editing tools. Once a comfort level is attained, users can then switch to standard mode, where the full functionality and powerful features are then available for increased productivity.

SilverFast's AACO is an excellent tool for the correction of dark, high-contrast areas of the image while preserving the details in the highlights. It operates automatically when selected but can also be manually manipulated. The intensity and the complexity of the shadows, which are to be lightened, can be adjusted without affecting the highlights of the image.

The extended print dialog offers the possibility of printing images or image areas selected by the frames in the preview. The selected images can be scaled, rotated or positioned manually on the print sheet.

The USM dialog and its preview windows may now freely be resized and enlarged. This can be done by click dragging the lower right corner of the window. Now, a better control of the image is achieved before scanning that allows a much larger preview of the final sharpening effects.

The support of the JPEG 2000 format enables SilverFast's strongest compression to process such data 3 to 7 times faster than Photoshop. In combination with SilverFast's HiRePP function, even 3GB files may be compressed and re-opened very quickly. It is important to note that Photoshop internally calculates with 15 bit, while SilverFast uses true 16 bit!

Scanner noise comes in random patterns and is mostly visible in the very dark areas of the scan. This is where the CCD is getting very little light to work with, so the difference between the signal from image details and the background noise from the CCD and other analog components is too small, resulting in image noise. If the image is scanned only once (normal scanning), the noise will be imprinted on the scan. When scanning with multiple sampling, the same image is rescanned repetitively. Since the noise patterns randomly change each time, SilverFast can differentiate the noise, cancelling it out if inconsistencies are present.

Scanner noise is clearly visible Scanner noise is eliminated

How does it work? With multiple sampling turned on, SilverFast will perform either 4, 8, or even 16 scans during scan time. You can specify the count, usually the more the better. After performing the scans, the single images are averaged together into one image. Since noise is random, a special averaging procedure will cancel only the noise but leave the image details untouched. There is a problem associated with this process: Every scan might not exactly be in the same position with reference to each other, so normal averaging would blur the resultant Multisampling scan. That is why Silverfast SE Plus has an intelligent auto-alignment, so no blurring effect can occur.

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