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Digital Imaging Solutions
In PracticeTEM Imaging
Visibly safer - Digital image evaluation using automatic particle analysis at 3M
Anja Christina Krzizek and Dr. Wolfgang Schöppel, Corpo-rate Materials & Process Laboratory - Microscopy Services, 3M Deutschland GmbH Dr. Peter Stallknecht, Olympus Soft Imaging Solutions GmBH
Joggers, emergency doctors and others out in the dark Cyclists, pedestrians, joggers and others are very much at risk when their visibility to others is low. Cyclists riding at night without a light take risks bordering on negligence. Joggers ought to wear reflective clothing when jogging in low-light conditions (eg, twilight). Emergency doctors and firefighters have special occupational wear which makes them more visible when working at night. Reflective materi-als also make traffic signs easier to see and read in the dark and help make stationary obstacles and construction sites safer. Producers of these reflective materials make tre-mendous efforts to continually move development of their products forward.
Retroreflecting stripes make firefighters much more visible during night-time operations. The headlights of oncoming cars light them up nicely. This gives drivers more time to brake if necessary.
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APPliCAtion REPoRt: DigitAl imAgE EvAluAtion using AutomAtiC PARtiClE AnAlysis At 3m
Visibly saferRetroreflection ensures better visibility in dark, twilight or other low-light conditions. A layer of micro-sized glass beads mounted on a layer of material is used to obtain retro-reflection. Surface density and size distribution of the glass beads are critical to re-troreflection. At the product development department of 3M Deutschland GmbH (3M‘s division in Germany), we use scanning electron microscopes (SEMs) to determine the-se factors. We use the Scandium image analysis platform for acquisition, management, archiving and evaluation of the images. Automatic particle analysis is used for image evaluation.
Light – right back at youA particularly effective type of reflection is termed retrore-flection. Retroreflection means that most rays of light stri-king a retroreflective surface bounce back in the direction they came from. very little light is lost due to lateral scat-tering. A retroreflective object appears that much brighter to the observer, the more closely the viewer‘s line of vision corresponds with the direction the original light source is pointing (at the object with the retroreflective material). take a car, for example. the light of the headlights is bounced right back from the object being illuminated by the car‘s headlights directly to the car, and thus to the driver in the car. this object lights up in the darkness and is thus more readily visible for the driver, who sees it sooner.
Retroreflection is due to a layer of tiny micro-sized glass beads. One of the primary tasks of the research division of 3M in Germany is testing new production methods for these beads. Automated digital image analysis is used to monitor whether the results satisfy demanding quality expectations or not.
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Pearls of glass Retroreflection is achieved using a layer of glass micro beads mounted on a layer of material. the diameter of these glass beads is typically about 50 micrometers. there are approximately 25,000 of them per square centimeter. the effectiveness of the retroreflection depends primarily upon the number, size and distribution of these little beads – and on their size distribution: ie, how many of the be-ads are what size? the 3m scotchlite™ reflective material uses special additives and processing steps for attaining the desired reflective response. the product development department of 3m in germany is where we test new proce-dures for optimizing product properties and the production processes. if we use an alternative production process, does product quality remain the same or does it improve? to find this out, we investigate the macroscopic reflective response and make extensive microscopic analyses of test products.
Retroreflection exploits optical refraction laws. All light rays that strike a micro-sized glass bead are refracted, reflected and once again refracted and deflected by a total of 180 degrees. This means they are reflected right back in the direction they came from.
Evaluating new procedures via image analysis in order to assess the effects of a new procedure on the quality of the product components, we use light microsco-pes as well as scanning electron microscopes (sEms) and computer-assisted image analysis. olympus soft imaging solutions products are used for digital acquisition, proces-sing, evaluation, management and archiving of the images. these products include the following: two Colorview ii digital cameras; software for light microscopy; an ADDA ii digital interface for analog sEms; and the scandium image analysis platform, including the „solution Detection“ for scanning electron microscopy. We save the images along with all measurement results and other associated docu-ments in a single network database located on a central server.
APPliCAtion REPoRt: DigitAl imAgE EvAluAtion using AutomAtiC PARtiClE AnAlysis At 3m
Micro glass beads from a production test run under the scanning elec-tron microscope (SEM). The image analysis software Scandium records the SEM image and calibrates it automatically (a). The image is filtered, binarized (b) and then automatically evaluated. The software separates the beads, detects them, measures the projected area of the beads and sorts them into size classes. The results appear in a sheet and are visible on the actual image. Each bead is digitally colorized according to its size class (c).
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APPliCAtion REPoRt: DigitAl imAgE EvAluAtion using AutomAtiC PARtiClE AnAlysis At 3m
Scanning Electron Microscopy A scanning electron microscope (sEm) is used for inves-tigating the glass beads. making these little glass beads retroreflect as powerfully as possible is what makes the light-microscopy investigation such a challenge. We place the samples at a tilt angle of 0° in the sEm. in order to avoid distance-related errors the working distance must be identical for each investigation. the image contrast bet-ween individual acquisitions via the live image on the com-puter monitor can be optimized interactively. to optimize image quality during and after acquisition, scandium offers numerous additional functions – eg, shading correction for eliminating uneven illumination, edge detection filters for enhancing edges and automatic contrast enhancement. optimal image contrast is important for subsequent image processing. Each image is automatically calibrated during acquisition to ensure accurate measurements.
Separation and detection the image is then binarized via suitable thresholds. now the scandium solution Detection can distinguish the glass micro beads from the background and detect them as particles without further user assistance. the „separator“ filter function ensures that any particles that appear joined together are correctly detected as separate particles and listed as such. We use a preset to exclude any glass micro beads from image analysis that are located along the edge of an image and which thus appear only partially.
How many are what size?now the image is ready for the actual image evaluation. Digital particle analysis is used to find out how many glass micro beads there are per square centimeter and the number of particles per size class. surface density and size distribution are the key criteria to be determined. Classifica-tion is defined with lower and upper limits for individual size classes. the size of the micro beads is measured according to their respective area projected. the software counts the micro beads automatically, measures their size and inserts this measurement data into a sheet where each bead ap-pears with an index number, area and the class it is in. the sheet can be statistically evaluated in scandium or Excel.
Coloring the circles the software makes it easy to see which beads belong to what class – beads are colorized accordingly. the smallest beads are green and the largest yellow. this color classi-fication does not alter actual image data in any way. the software draws the colors in what is known as the overlay, which is just like a digital transparency placed over the actual image. When making a presentation using these results, this color classification can be transferred to the unprocessed original image. Another way of demonstrating size distribution, is by generating a bar graph of the results – one of several display options.
For those of us working in the product development department, surface density and size distribution of the micro glass beads are suitable measurement quantities which enable us to compare the results of various test runs. using digital image analysis provides decisive assistance in further developing our products and production processes.
ACknoWLEDGEMEntS
Text written in close collaboration with:
Anja Christina Krzizek and Dr. Wolfgang Schöppel, Corpo-rate Materials & Process Laboratory - Microscopy Services, 3M Deutschland GmbH, Carl-Schurz-Strasse 1, D-41453 Neuss, Germany
Image source: 3M Deutschland GmbH
All rights including translation are reserved. Any and all forms of reproduction must be authorized by Olympus Soft Imaging Solutions. We are unable to assume any liability for unrequested consignments received.
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