Image Quality Which Metric Should I Choose

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Image Quality Which Metric Should I Choose?

• Jed Hancock
• Optical Sciences 521

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Image Quality Criteria

• Image quality criteria defines the imaging
  performance of an optical system
• This is how you know you are done
• Most often a complex process
• The criteria is usually described by multiple
  image quality metrics (WFE, MTF, etc)

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Image Quality Metrics

• Evaluation of metrics
• Typically modeled (ray trace codes) then tested
  (calibration)
• Image quality is affected by the mechanics
• Optical engineers tool bag
• Opto-mechanics Tolerancing, statics,
  deflections, thermal effects, vibration
  isolation, material properties, precision
  adjustments, mounting of lenses, windows,
  mirrors..

4
Spot Diagrams

• Effective for applications where ( ¼ ?)
• Specific types of aberrations can be determined
• Geometric or RMS radius
• Geometric metric

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Ensquared Energy

• Geometric estimate of energy on a pixel
• Imaging and non-imaging applications where (¼ ?)
• Geometric metric

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Wavefront Error

• Optical path difference between the actual wave
  and reference wave
• Measured in the exit pupil plane
• Aberrations can be determined by wave fan plots
• Geometric metric

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Modulation Transfer Function

• The optical transfer function (OTF) is the
  autocorrelation of the complex
• pupil function and it is also the Fourier
  transform of the point spread function
• The MTF is the modulus of the OTF
• Extended scenes, small aberrations, complete
  system analysis
• Geometric and diffraction metric

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Point Spread Function

• The point spread function captures diffraction
  effects or the wave
• nature of light
• Small aberrations ( ¼ ?)
• Youngs double pin hole experiment
• Diffraction metric

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Strehl Ratio

• Best for small aberrations ( ¼ ?)

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Geometric vs. Diffraction
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Choose Appropriate Metrics

• Often times more than one image quality metric
  should make up the
• criteria, this depends on the application
• If WFE were the only image quality metric chosen,
  the effect of an
• obscured aperture on image quality could be
  overlooked