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Digital Conversion of Single-Use Camera Ranging Lab

This article discusses the problems with the traditional ranging lab method and proposes a digital method using slanted-edge analysis to determine the best focus. The issues with the method are inconsistent results and the influence of multiple systems on the MTF calculation. Possible solutions are suggested to address these problems.

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Digital Conversion of Single-Use Camera Ranging Lab

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  1. Digital Conversion of Single-Use Camera Ranging Lab Michael Spaeth SUC Tech Center Eastman Kodak Company

  2. Ranging Lab

  3. Problems with Ranging Lab • Negatives are read via microscope • Tiring for observer • Human differences • What you see as a line pair, I may not • Red tint of color AgX negative

  4. Digital Method - Theory • Digitally sample images • Whether with CCD array or film scanner • Run images through a slanted-edge test to find MTF • Compare MTF’s to find ‘best’ focus

  5. Slanted-Edge Algorithm • Slanted-Edge software www.pima.net/standards/iso/tc42/wg18/wg18__sfr_matlab_page.htm • Written in Matlab • Needs high contrast in target • Needed to be converted to IDL

  6. Slanted-Edge Test - Matlab

  7. IDL Conversion Test

  8. Ranging Lab Program • Loops Slanted-Edge Analysis • Compares MTF values to determine ‘best’ focus

  9. Ranging Lab Program Demo

  10. Problems With Method • Inconsistant • Does not return same value each time through • Possible Reason – • low contrast in images, creating high error in MTF calculation • Possible Solution – • use target with higher contrast • alter image to raise contrast

  11. Problems With Method • All the plots are the same • Possible Reason – • multiple systems influencing system MTF • Possible Solutions – • Analyze all systems other than optics and subtract MTF for these systems • Reduce number of systems in process

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