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Pressure Sensitive Film - Summary of Responses

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  • Pressure Sensitive Film - Summary of Responses

    Here is a summary of the results we recieved in response to our query on the analysis of Fuji Pressure Sensitive Film. Our apologies for the delay. This has been along time coming.

    Miss Emma A C Johnson
    University of Teesside
    Middlesbrough, England
    a.. Sensor Products Inc. USA offered to provide this service for us. They have a system called "Topaq" that
    read and interprets sheets of the fuji film.
    a.. Matthew P. Reed, Ph.D. of the University of Michigan Transportation Research Institute suggests using an ordinary flatbed scanner and a do-it-yourself calibration.
    For the calibration, subject samples of your film to known pressures (weights applied to film held between two flat metal plates works well for many pressure levels). Contact area x Weight gives you the control you need to ensure that you span the range of experimental pressures.
    Scan the calibration samples with your flatbead scanner in 8-bit grayscale mode. Use a program such as NIH Image to compute the mean and standard deviation of the calibration exposures in terms of pixel value (0 to 255). If the coefficient of variation is too high (you be the judge), your exposures weren't sufficiently uniform -- a
    flatter calibration surface might be in order. Along with the calibration samples, scan two or more pieces of material whose color and reflectance you believe will remain stable. The color charts
    Fuji distributes with their film are a good choice (store your film
    and these reference samples in a dark place).

    You will find that the film responds nonlinearly to applied pressure.
    The particular response you get will depend on your scanner, the
    duration of applied load, temperature, humidity, and the age of the
    film (but mostly the first two). You will also find that the film
    repeats very well under controlled conditions (e.g., your
    calibration). The duration of applied load is important -- you must
    calibrate using a load history that is similar to your application.

    Your subsequent analysis of experimental samples is straightforward.
    Scan the exposed film and transform the pixel values into pressures
    using your calibration curve. NIH Image can facilitate this as well
    (the macro language is very useful). Also scan your reference
    samples to verify that your scanner hasn't drifted. Note: Don't use
    the Prescale film calibration samples as your reference. The film
    density changes with time, even if you protect the film from light.

    a.. Sylvain Couillard of the Human Performance Lab, University of Calgary, Canada have found that the films can be scanned and saved onto a computer to be analysed with Adobe Photoshop by using color intensity.

    b.. Alan M. Wilson of The Royal Veterinary College in Herts, UK said to find a scanner and a computer image analysis package, for instance NIH image which you will find referenced in BIOMCH-L archives and downloadable.
    a.. Tyler Kress and Dr. David Porta of The University of Tennessee and Bellarmine University, Kentucky used the color chart provided with the film for their analysis.
    a.. Joseph E. Hale, Ph.D. of the Minneapolis Sports Medicine Center found that analysis of Fuji Film can be readily (and inexpensively) performed using a digital camera/scanner and image analysis software. He says, 'I worked with Fuji extensively during my graduate work at the University of Iowa; our methodology is summarized in the following article':
    Hale, J.E., and Brown, T.D.: Contact Stress Gradient Detection Limits of Pressensor Film. Journal of Biomechanical Engineering 114:352-357, 1992.
    a.. Jim Funk of the Automobile Safety Laboratory, Charlottesville also suggests using a standard optical flatbed
    scanner and NIH Image. He writes, ' To correlate grayscale values to stress values, I applied a
    calibration curve. The calibration was done using a simple in-house device
    that applied a known force (delivered by slowly and carefully lowering a
    weight) over a small circular area via a lever arm. Edge effects were
    mitigated by placing a thin piece of rubber padding under the point of
    weight application. As I recall, the relationship between stress and
    average grayscale value was somewhat nonlinear.'
    a.. Priv. Doz. Dr. Dieter Rosenbaum of Funktionsbereich Bewegungsanalytik - Movement Analysis Lab
    Klinik für Allgemeine Orthopaedie has analyzed fuji film with a commercial scanner and a freeware program (OSIRIS). They have calibrated their fuji samples in a material testing machine and have used
    these results to convert the color intensity into pressure values. This was their fourth project using fuji film and it worked well.
    He states, 'In the previous projects we used a digital image analysis system we had access
    to (for measurements in the subtalar and chopart joint) or a dedicated system
    that we rented from our german supplier of fuji film (retropatellar
    measurements). I did not see a major disadvantage of using the simple
    cheap-and-easy method (scanner & freeware)'.

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