VueScan Scanning Software: General Overview

© Thomas Gade

Index



VueScan serves two primary purposes: scanning the image and processing the raw data. The 'Preview' and 'Scan' actions both involve both steps—meaning scanning (or opening a file) and processing. The main difference between a preview and a final scan is that a preview is typically not saved, and it scans a larger area from which a specific crop is then selected. It is also possible to save the data unprocessed as raw files after scanning and process them at a later time.

Scanning

Scanning is the process of digitizing images using hardware devices. Fundamentally, we distinguish between flatbed scanners and film scanners. They feature one (or more) built-in light sources, film holders or glass surfaces to place originals, and complex scanning technology, which generally consists of a scan line (CCD sensor) along with the optics in front of it and a movement mechanism. In a flatbed scanner, the scan line moves step-by-step (or line-by-line) along the original to scan it. During this process, brightness measurements are performed point-by-point at precisely defined intervals. For color originals, this is done for red, green, and blue light. This data is combined into a raw file for an image. Digitizing is similar to the exposure process in photography: dark images require longer exposure times than bright ones. Exposure control is managed by varying the sampling time and/or controlling the lamp brightness. Exposure metering takes place after the preview and after defining the image by setting a precise crop area. There are film scanners that can automatically advance film strips from frame to frame or change mounted slides. On a flatbed scanner, multiple originals can lie side-by-side, or multiple crops can be digitized from one large original. These operations can be carried out with VueScan. The result of a scan process is a raw file that is initially stored in the system memory (RAM).

When 'single-pass multi-scanning' is selected, each line is read multiple times by the CCD sensor, and the results are combined into an average value. When 'multi-pass multi-scanning' is selected, the entire crop area is fully scanned multiple times, and the results are likewise combined into an average value. The 'multi-pass' process requires a precise scanner that can perform the movement of the scan head multiple times in succession with absolute consistency.

The user can decide whether the raw file is initially saved to the hard drive to be corrected later or if processing takes place immediately after reading the data.

VueScan also uses the term 'Scan' even when the aforementioned digitization process has already been completed and the raw data is being read from a storage drive for further processing. In other software programs, this would be called 'Open File'. For this reason, the following lists where the raw data can originate from when 'scanning' with VueScan:

1. As the result of an immediately preceding digitization of an original using a scanner

2. By opening raw data from previous scans ('Input|Source' set to 'File')

3. By opening raw data from a digital camera ('Input|Source' set to 'File') – VueScan is compatible with many RAW formats

4. By opening other image files in TIFF and JPEG formats

5. The raw file is already located in the system memory **

** VueScan retains a raw scan in the system memory. You can use it to output differently processed copies without having to re-scan. It is possible to output images with and without ICE correction, with and without sharpening, with and without various color corrections, etc., simply by clicking 'Save' after each parameter change. This is an excellent feature that offers highly interesting possibilities for image optimization.

If a preview is initiated for a film strip containing multiple frames, a separate data buffer is created for each file, allowing you to switch between individual frames without additional previews or scans. This requires sufficient RAM. The total memory allocation is limited by the settings 'Prefs|Image Memory', 'Prefs|Preview mem (MB)' (for previews), and 'Prefs|Scan mem (MB)' (for scans). If more memory is required, the oldest data buffers are released until enough memory is available for a new preview or a new scan.

When the 'Input|Source' setting is set to 'File', files are opened and treated as if they came directly from a scanner. The 'Input|Mode' setting is used to specify the scanner type from which the raw data (!!) originated. This is helpful for subsequent color and tonal corrections. The data to be processed can be unprocessed raw data from scanners as well as RAW files from digital cameras. If files are opened that have already been processed, no specific device should be selected under 'Input|Mode'.

When the preview image is scanned, the exposure time is set to 1.0. The scanned area is the entire preview area (meaning no specific 'crop'). The resolution is set to a value that produces approximately 1 million pixels.

During the final scan, the exposure time is calculated either from the preview or from manual settings, and the scan area is a sub-section of the preview area (bounded by the flashing crop frame). If the resolution is set to 'Auto', a resolution is used that produces approximately 4 million pixels.

Processing

Generating the raw data is only half the battle. Typically, scanning also includes processing the data into images with a natural-looking color balance, contrast, and brightness gradient. The processing specifications are applied to the preview and the subsequent scan. If the scanner is appropriately equipped, the first step compares the infrared data with the RGB data to prepare for dust and defect correction.

Next, the cleaning filter (if activated) is applied. Its job is to remove dust and scratches using the infrared data by filling these points with the immediate surrounding color. This filter also reduces film grain.

Infrared data is only provided by scanners with an IR channel. If this channel is not present on your device, these settings are turned off and unavailable.

If the 'Output|Raw file' setting is activated and 'Output|Raw output with' is set to 'Save', the data is saved into a TIFF file. This raw data can be reprocessed later by setting the 'Input|Source' option back to 'File'. Note that the IR channel data, if present, is saved as part of this raw file.

Next, the 'restore colors' and 'restore fading' filters are applied (if turned on). This means that the entire image is analyzed to determine its original colors in order to correct color shifts and fading. (Note: 'restore colors' frequently leads to unusable results.) Sharpening is applied next. In principle, image sharpening should only be performed right before using an image, such as for printing or displaying it on the web. For this reason, sharpening should remain turned off when creating archival files. Other software tools deliver better sharpening results than VueScan. However, if you are using VueScan directly for printing, enabling sharpening may be useful and should be tested.

The final step is color correction. The settings from the 'Color' tab are used to establish the final colors of the saved images.

Following color correction, previews are displayed in the preview window, and scans are saved as TIFF, JPEG, PDF, OCR text, and/or index files according to the settings in the 'Output' tab.

Color Balance

One of the most critical attributes of an image is its color balance – ensuring that neutral colors appear neutral and other colors look true to life. VueScan's default setting for 'Color|Color balance' ('White balance') can achieve this automatically for most images.

However, VueScan's automatic white balance is not ideal for unusual lighting conditions during capture. It alters the light of a sunset so that the ground appears gray instead of orange, and scans of flowers may look less vibrant than they should. For such images, changing 'Color|Color balance' from 'White balance' to 'Neutral' yields better results.

When scanning slides, 'Input|Media' should be set to 'Image'. (Note: The alternative 'Slides' setting exists, but results may vary depending on the scanner model used.)

By setting 'Color|Color balance' to 'Manual', colors can be adjusted manually. This process requires some getting used to when using the three separate sliders for Red, Green, and Blue, as other programs offer more user-friendly solutions. However, VueScan features a gray eyedropper tool.

To use it, right-click (Mac OS: hold the Control key) on a section of the image that should contain a neutral tone (e.g., a gray shadow). You can click on various areas that you assume should be neutral gray. The remaining colors will adjust accordingly each time. Once you hit a good point, the overall color balance of the image will be correct. With a little practice, this is a powerful tool. You can reset the color balance back to 'White balance' by double-right-clicking (Mac OS: double-click while holding the Control key).

Scanning Multiple Originals / Batch Scanning

Using the 'Input|Batch scan' setting allows multiple images to be scanned and processed automatically in succession. Some scanners can eject a processed frame and feed the next one, or advance a film strip from frame to frame automatically. Flatbed scanners that accommodate multiple images on their glass bed can be controlled to scan one image after another.

The speed of batch scanning can be increased by skipping the preview for each individual image. This is feasible if the exact same crop area can be used for all images. Furthermore, uncheck the settings 'Crop|Auto offset' and 'Crop|Auto rotate'. Using the 'Input|Lock exposure' setting allows you to lock the same exposure time for all subsequent scans, minimizing measuring overhead. This is not recommended for mixed batches with varying contrast and brightness levels.

VueScan allows you to scan multiple photos or selections on a flatbed scanner using two different methods.

The first method requires the images to fit precisely into individual fields of a grid and be positioned accordingly. In the 'Crop' tab, settings are adjusted to define how many images are arranged side-by-side ('Crop|X images') and vertically ('Crop|Y images'), along with spacing between the images and more. This method requires some getting used to but is highly practical.

The second option bypasses the grid layout but requires a large amount of RAM and a fast computer when scanning at high resolutions:

1. Enable 'Input|Scan from preview'
2. Click the 'Preview' button
3. Define the first crop area with the mouse
4. Click the 'Save' button (looks like a floppy disk), then define the next crop area with the mouse, and so on.

Repeat this procedure every time you place a new batch of photos, slides, or film strips onto the flatbed scanner.

Using Raw Data

VueScan allows you to save the raw data from a scan session via 'Output|Raw file'. This file contains data directly from the scanner's CCD sensor, free of any color correction or modifications. None of the settings in the 'Filter' or 'Color' tabs affect the raw file unless 'Output|Raw output with' is set to 'Save'. In that case, settings for rotation, mirroring, infrared cleaning, and grain reduction are applied. Grain reduction should never be enabled in VueScan, as better external tools exist for this purpose.

Saving raw files offers two major advantages: scanning is much faster without subsequent image processing, which is highly beneficial when handling large amounts of images that must be loaded manually. The actual processing can run unattended in the background later on. Additionally, the saved raw scans serve as permanent source material for all types of copies. Re-scanning only becomes necessary if you need to enlarge the crop area, require a higher resolution, or if vastly superior scanning technology becomes available.

For batch processing raw data, the source and media settings in the 'Input' tab are adjusted. First, set 'Input|Options' to 'Advanced' (or click the 'More' button in older versions) and reset the software to factory defaults using the 'File|Default options' command.

Set 'Crop|Preview area' to 'Default', 'Crop|Crop size' to 'Maximum', 'Crop|Y images' to 1, and uncheck all boxes in the 'Output' tab except for 'Output|Raw file' (which must be enabled). As each frame is scanned, files named scan0001.tif, scan0002.tif, etc., will be generated. You can change the target folder and file naming structure using the 'Output|Raw file name' option.

To process these raw files later, go to the 'Input' tab and set 'Source' to 'File'. Under 'Input|Files', select the first image in the series (typically scan0001.tif). Under 'Input|Mode', select the exact scanner model that originally generated the files. All other settings are then configured exactly as if the files were being processed live from a scanner.

Set 'Input|Batch scan' to 'All' to process all files in bulk, or select 'List' to manually input specific frame numbers. Entering '1-3,5,7', for instance, will process frames one through seven while skipping the fourth image when the 'Scan' button is pressed.

Maximizing Image Quality

The underlying concept here is to scan each pixel multiple times and then average the values. Each doubling of the sampling passes increases the effective number of useful data bits by 1. For instance, if a 10-bit scanner like the Nikon LS-30 samples each pixel position four times during a single scan pass, it effectively yields 12 bits of usable image data. There are several ways to obtain multiple exposure readings. The first is 'single-pass multi-scanning'. Some scanners can sample each pixel position multiple times before moving the scan head to a new position. Film scanners that support 'single-pass multi-scanning' include: Minolta QuickScan 35, Scan Dual, Scan Dual III, Scan Multi, Scan Multi Pro, Scan Speed, Scan Elite, Scan Elite II, and the Nikon LS-2000/LS-4000/LS-8000 models.

The second technique is 'multi-pass multi-scanning'. Most scanners are capable of performing this function. However, some devices reset the scan head alignment imprecisely after each completed scan pass, meaning this task is not always achieved with satisfactory results.

Another option is to scan at a high resolution and then average adjacent pixel blocks. For example, if you set the resolution to 2700 dpi and average each 2x2 pixel block, you obtain a higher-quality 1350 dpi file. Scanning directly at 1350 dpi in this scenario simply means that all other pixels and lines are discarded. Conversely, scanning at 2700 dpi with 'Output|TIFF size reduction' set to '2' averages the 2x2 pixel blocks, increasing the number of effective bits at this resolution by 2. This method is impractical if data is required at the scanner's maximum possible resolution, but it is an interesting alternative when using flatbed scanners that are marketed with unrealistically high, nominal resolution specs.

File Formats

VueScan offers the following output formats: TIFF (.tif), JPEG (.jpg), PDF, and OCR. Every index print is saved as a BMP file. JPEGs can be saved at 8-bit for black and white (grayscale) and 24-bit for color images. When an image is saved as a JPEG, some image data is lost even at the highest quality (and lowest compression) setting. This loss compounds if the file is edited and saved again. Therefore, it is better to initially generate TIFF files and edit them until no further significant changes to the archival image are expected before creating JPEG copies. Since storage is relatively inexpensive, it is highly recommended to preserve the TIFF versions permanently, even though files in this format can be quite large.

There are six different TIFF options: black and white images (grayscale) require a single color channel, while color images possess three color channels (Red, Green, Blue). A black and white image can get by with one bit per pixel if it only needs to distinguish between pure black and white (e.g., text documents). If tonal values ranging from black to white with various shades of gray are present, 8-bit or 16-bit per pixel is required. Color photos feature three channels, each with 8-bit or 16-bit color depth. Scanners and digital cameras often utilize different internal bit depths ranging between 8 and 16 bits per channel. Values above 8-bit can only be fully utilized if the output file is saved at 16-bit per channel.

Various scanners feature a fourth channel for infrared light, which is used for automatic dust and scratch detection. VueScan offers the option to save these four channels together in a 64-bit file as Red-Green-Blue-Infrared (RGBI). Additionally, the infrared channel can be output separately as a standalone 16-bit file.

The raw scan files are output in a linear format when using more than 8 bits per channel, and with a gamma of 2.2 when using only 8 bits per sample. The final saved TIFF files always feature a gamma correction corresponding to the selected color space (1.8 for Apple RGB, ColorMatch RGB, ProPhoto RGB, and ECI RGB, and 2.2 for all other color spaces). It is completely normal for raw scan files in linear format to look very dark initially.

TIFF data can be compressed. VueScan uses 'CCITT Group-IV compression' for 1-bit files and 'LZW compression' for all other formats. The latter is slightly slower when saving but reduces the required storage space by roughly 40%. The file size of JPEGs can be controlled using the 'JPEG quality' setting, with defined values ranging from 75 (highly compressed, medium quality) to 95 (low compression, high quality).

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Table of Contents:

General

Introduction

Calibration

Scanning black-and-white film

Scanning color negatives

Scanning slides

Identifying film types

Tabs

Source

Crop

Filter

Color

Output

Settings

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