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KODAK PROFESSIONAL: Technical Information Bulletin

Minimizing Retouch and Rework Due to Dust
 
 

KODAK PROFESSIONAL HR 500 Film Scanner
KODAK PROFESSIONAL HR 500 Plus Film Scanner
KODAK PROFESSIONAL HR Universal Film Scanner

Contents

10 September 2002

 

Introduction

Dust is a problem for any film scanner.

Many scanner users have little or no interruption in productivity due to dust. Other users experience significant challenges with dust. Dust problems depend on the type of scanner, the environment, and the workflow. Customers who own several types of scanners may find some models immune to dust and others to be sensitive to dust. The opposite may be true at another location that has a different workflow.

If dust is on the scanner's sensor or the optical path, the scan will have streaks. If dust is on the film, the scan will have spots. This can be avoided by proper cleaning techniques or by using DIGITAL ICE technology which automatically corrects many scan defects. DIGITAL ICE technology is included in the KODAK PROFESSIONAL HR 500 Plus Film Scanner and KODAK PROFESSIONAL HR Universal Film Scanner when used with KODAK PROFESSIONAL Digital Print Production Software (DP2), KODAK PROFESSIONAL HR 500 TWAIN Data Source, or KODAK PROFESSIONAL HR Scanning Software.

This document contains dust control and abatement measures that can improve productivity of linear array scanners.

 

Linear Array Scanners

Linear array scanners are able to quickly scan any file size (resolution) from small to large. They employ CCDs containing 1 row of Red photosites, 1 row of Green photosites, and 1 row of Blue photosites. (Note: It is more accurate to call CCD pixels "photosites" because they gather light photons and convert the photons collected to electrical charge.) In the HR Scanners, there are up to 6,002 photosites for each of the 3 colors. The number of active photosites for each scan depends on the magnification used and the film size. During a scan, film is moved while the rows of CCD photosites are turned on to capture 1 vertical line of image data, turned off and reset, then turned on again to capture the next vertical line of image data. The light source is nominally white light and all 3 colors are simultaneously captured each time a vertical line of data is taken. The HR 500 Plus Scanner and HR Universal Scanner capture infrared data from images. DIGITAL ICE Software uses this data to automatically remove most of the dust and some scratches from scans.

The scanner or host software must compensate for 3 rows of Red, Green, and Blue photosites that are side-by-side in the CCD by matching each vertical line of Red data with Green and Blue data taken from precisely the same vertical line on the image. Any defect that appears at photosite #4354 Red will appear in pixel #4354 Red for every vertical line of data captured. This causes photosite #4354 Red to be part of a "streak" horizontally across the entire scan. If the source of the problem at photosite #4354 is not removed, subsequent scans will have a streak across the image in the direction the film moves while being scanned at the same location.

 

Area Array Scanners

Area Array Scanners, like the KODAK PROFESSIONAL RFS Film Scanners, operate similarly to digital or film cameras. The entire image being scanned is captured at one time. Usually these scanners have one area array CCD so there must be a subsystem which changes the light source to produce Red, Green, and Blue light. Each image must have data captured in three separate exposures. The physics of creating area array CCDs tends to limit resolution/file size.

 

Diagnosing Streaks in Linear Array Scanners

Continuous horizontal lines across images occur because the scanner calibration has been compromised by dust. Dust streaks are usually 2 pixels wide or wider. To determine the width of a streak, view the image at 1:1 or 100% magnification only. Other magnifications interpolate pixels and may result in misleading pixel counts. Streaks that are approximately 10 - 20 pixels wide (depending on magnification) are caused by large objects like a human hair. Dust that causes streaks smaller than 10 pixels may be so small that you need a magnification loupe to see it on the scanner light bar. Very small dust particles may cause streaks that are 2 pixels wide, but more often the streaks will be 3 pixels wide or wider. One-pixel streaks are only caused by electronic problems, never by dust.

Note: The following information applies to non-negative images (slides). If negative film is scanned, substitute "Light" where "Dark" appears, and vice versa.

Symptom

Causes

Recovery Method

Dark Streak(s)

Dust fell on the light bar after the scanner was calibrated.
Most common causes are:
- dust on the film prior to scanning, or
- dust in the scanning room atmosphere.

Clean the light bar, then calibrate the scanner.
See Cleaning the Light Bar

Light Streak(s)

Dust was on the light bar during the previous calibration. The dust fell off the light bar causing a streak that is lighter than the pixels above and below it.

Clean the light bar, then calibrate the scanner.
See Cleaning the Light Bar

Combination Streak(s) of Light and Dark Near Each Other

Dust was on the light bar during the previous calibration. The dust moved to a nearby location. This produced a light streak where the dust used to be and a darker streak at the new location.

Clean the light bar, then calibrate the scanner.
See Cleaning the Light Bar

* Can be neutral density or colored. See explanation below.

Why Streaks Can be Neutral Density or Colored:
If the dust particle is large and centered on the light bar, the shadow it casts on the linear CCD array covers all 3 colors in the linear CCD array. The HR Scanner linear CCD array has 3 rows of sensors side-by-side. The first vertical row of 6002 pixels has a red filter over it, the center row has a green filter, and the third row has a blue filter. When the dust particle is small or is located on one side of the light bar, the shadow that falls on the CCD may cover only 1 or 2 rows of photosites on the CCD. This results in colored streaks because 1 or 2 colors captured will be brighter or dimmer compared to the neighboring colors.

 

Operating and Maintenance Tips to Reduce Streaks

 

Understanding the Calibration Process

When you calibrate HR Scanners, every photosite in the CCD is "linearized" so they have the same response to light. If dust is on the light bar during calibration, some of the pixels will be darkened by the shadow of the dust. When calibration is performed, every brighter pixel is reduced in level to match the dimmest pixels. There will be no problem if the dust never moves. Streaks happen when the dust moves after calibration or if new dust appears while scanning. When the dust moves, the pixels that were originally shadowed by the dust will now be brighter than their neighboring pixels. The pixels that become shadowed by the dust movement will now be darker than their neighboring pixels. This is why it is important to eliminate as much dust as possible in the scanning room and why it is important to clean the light bar before you calibrate the scanner.

Calibrate the scanner after each magnification or file size change because, when magnification changes, the light falling on the CCD changes and each pixel in the CCD requires a new and different calibration value.

  

Cleaning the Light Bar

Why:
Removing dust particles from the light bar surface prevents streaks in scanned images.

When:
Clean the light bar before calibrating the scanner. This sequence is important!

How:
Using a dry, microfiber cloth, make a single vertical wipe along the light bar. If additional cleaning is needed, dampen (do not soak) the microfiber cloth with 90% or higher isopropyl alcohol. Do not use rubbing alcohol! E-Wipes, a pre-packaged isopropyl alcohol cleaning pad, may also be used. We do not recommend any other cleaning method. Use only dampened materials to clean the light bar. Excessive moisture is not recommended.

 

Calibrating the Scanner

Why:
CCD response changes as room temperature changes and as time passes. Lamp light output changes slightly over time. The materials used in the HR Scanners expand and contract very slightly in response to variations in temperature. We recommend you calibrate HR Scanners every 3 hours. Some customers prefer to calibrate every 2 hours, others prefer to wait until 4 hours. The HR Scanner application software may contain an internal timer that forces recalibration at a set interval. The user can set the interval. Each customer needs to determine whether the default (3 hours) is appropriate or whether they should calibrate more or less often.

With the latest versions of firmware, HR Scanners remember calibrations from magnifications previously used. If you change magnification and then return to a previous magnification, you can use the same calibration again, or you may choose to recalibrate. The software application will present these options to the operator.

When:
The application software (DP2, TWAIN or HR Scanning Software) requires that you calibrate the scanner every time the magnification, resolution, or file size changes so all the CCD pixels are linearized to the new pattern of light. When scanning long jobs that do not require a magnification change, calibrate the HR Scanner approximately every 3 hours.

How:
Each software application that can control the HR Scanner has a Calibrate button located on the capture screen. When you click the Calibrate button, the scanner is calibrated in a short period of time. Clean the light bar before calibrating. Sites with a low occurrence of streaks do not need to clean the light bar before every calibration (once a day or once a shift may be enough).

 

Maintaining a Clean Scanning Environment

Each customer site has different challenges regarding dust control and abatement. This information covers a range of possible solutions from simple and inexpensive to elaborate capital improvements. Appropriate measures for a site depends on the productivity goals for the digital workflow and how those goals balance with the cost of making the scanning environment cleaner. The Basic items are low cost or no cost unless removal of carpet and replacement with hard flooring is required. The items under More Serious Measures can be inexpensive or significant depending on the building and materials. Extensive Measures need not be prohibitively expensive but may be necessary for sites that want to minimize the need for image rescanning and retouching.

Why:
Static attracts dust. When static is reduced or eliminated, the only remaining causes of dust or streak artifacts are (1) dust on the film before the scanning operation begins, and (2) dust in the environment. If the scanner environment is dusty, some dust will inevitably make its way to the light bar or onto the film even if static-reduction measures have been taken.

How -- The Basics:

  • Use hard flooring material that does not produce fibers or dust that can become airborne.

  • Avoid carpets.

  • Clean the floors regularly to keep dust under control.

  • Use cleaning methods and equipment that do not exacerbate the dust problem (vacuum cleaners with HEPA filtering or other micro filtering methods, wet mopping, etc.).

  • Dust work surfaces and equipment regularly. Use techniques that remove the dust from the room rather than spreading it around.

  • Do an occasional "deep cleaning." Clean under all the equipment in the room to remove hidden dust.

  • Do not allow heat or air conditioning outlets to blow on the scanning station.

  • Do not allow fans from other equipment to blow on or towards the scanner.

How -- More Serious Measures:

  • Run portable HEPA air filters in the scanning area at all times. Filter airflow capacity should filter the air volume in the scanning area at least 4 times an hour. Regular filter maintenance is critical to keep the filters effective. Portable HEPA filters are available from Sears, Honeywell, Enviracaire, Bionaire, Amairecare, EnviroPro, Mitsubishi, Panasonic, and many others.

  • Use static-reducing floor mats at entrances.

  • Establish clothing guidelines for the scanning area. Eliminate fabrics that "shed."

  • Ceiling materials should not shed fibers into the scanning area.

  • Seal gaps in floorboards, window/door openings, and where walls meet the ceiling and floor. This is especially important with older buildings.

How -- Extensive Measures:

  • Pressurize the scanning area with filtered air. When doors open, only filtered air can leave the scanning area which keeps dusty air outside. This clean-room technique may not be prohibitively expensive. You can purchase equipment to achieve a suitably low level of dust contamination and which is far less expensive than serious clean-room setups.

  • Have employees wear disposable clean suits in the scanning area.

 

Controlling Static

Why:
Static attracts dust. Any dust on the film or in the air eventually makes its way to the scanning area.

When:
At all times.

How:

  • Use film cleaners with a forced air ionization station after the Particle Take-off Rollers (PTR) to remove static caused by cleaning the film.

  • Control the humidity in the scanning area. Avoid low humidity which promotes the build-up of static charges.

  • Operators should wear clothing that reduces static charge (cotton is better than silk, wool, or synthetics).

  • If necessary, use dust-free, anti-static containers to transport the film. We recommend the SIMCO Static Removal Kit (see information below).

  • For minor static issues or very infrequent streak/dust problems, install anti-static brushes in the HR Scanner Long Roll Transport. Anti-static brushes are being installed in new Long Roll Transports. Kodak Service Representatives will retrofit early-model Long Roll Transports at no charge to the customer.

    Mod 2 will not be effective for customers with regular occurrences of streak/dust problems. It is not recommended as a solution for moderate to severe dust/streak problems. In these instances, we recommend the SIMCO Anti-Static Ionizer Kit.

  • For moderate to severe static/dust problems, Empire Tech Solutions stocks ionizing blowers which can reduce the static charge on film and around the scanning area.

    Empire Tech Solutions, Inc.
    1151 Pittsford Victor Road
    Pittsford, New York 14534
    Phone: 585.924.8980
    www.empire-tech.net

  • For customer sites where film is spooled on cores without flanges, install KODAK Anti-Static Film Core Flanges. These conductive flanges are placed on the spindles to support the film and reduce static build-up as the film unspools and is taken up again during scanning.

    This item for the HR Scanner Long Roll Transport is available beginning May 2002. To change to this type of flange, contact your Kodak Service Representative and request Mod 4 for the Long Roll Transport.

    Mod 4 is included with all new Long Roll Transport accessories; serial number 208 and higher. The new conductive flanges have a metal center section (the original flanges are completely plastic).

    Note: If you use reels for long roll film, conductive flanges will not reduce static in and around the Long Roll Transport.

 

Always Use Clean Film

Why:
Dust on the film is a major contributor to visible dust artifacts or continuous streak problems. Dust causes retouch work and can increase the frequency of continuous streaks if the dust transfers to the light bar during scanning or fast forward/fast rewind operations.

When:
For highest productivity, always clean the film before scanning.

How:
We recommend film cleaners that use multiple large diameter PTRs followed by an ionized air station that blows air over the film. This process removes the static charge that builds up from the film being unwound from the spool and passing over the PTRs. Some customers clean their film twice to make sure all dust is removed and to return the film to the original order in which it was spooled.

Transport cleaned film in bags or other containers that do not hold a static charge (conductive plastic or metal). Information that must travel with the film should be on a material that will not shed fibers on the film. If the information must be on paper, keep the paper out of contact with the film.

Static removal measures such as orange anti-static cloths (flapping or stationary) are minimally effective. They are not recommended because the cloths can shed fibers onto the film.

The film cleaner area should be as clean as the scanning area. If the area around the film cleaner is not kept clean and dust free, film can attract dust during the cleaning process! The most effective cleaners have PTR shafts parallel to the table or floor. Vertically mounted PTRs often put one edge of the film so close to the table that any dust from the table is attracted back to the film. Clean PTRs regularly and replace them when they are no longer sticky enough to be effective.

 

Using Compressed Air

If compressed air is needed, direct it away from the scanner area. Never direct an air stream towards a scanner or a table holding a scanner because there can be dust on these surfaces. If dust remains unmoved, it will not cause a problem. If the dust is disturbed by the air stream, it can rise into the air and possibly settle on the light bar which will cause streaks.

Kodak and Kodak Professional are trademarks of Eastman Kodak Company.

TIB7024

Technical Information Bulletins provide information of limited or specific application. Responsibility for judging the applicability of the information for a specific use rests with the end user.