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Image Quality –Which Metric Should I Choose?

Image Quality –Which Metric Should I Choose?. Jed Hancock Optical Sciences 521. 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

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Image Quality –Which Metric Should I Choose?

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  1. Image Quality –Which Metric Should I Choose? Jed Hancock Optical Sciences 521

  2. 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…)

  3. 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 λ) • Specific types of aberrations can be determined • Geometric or RMS radius • Geometric metric

  5. Detector outline Ensquared Energy • Geometric estimate of energy on a pixel • Imaging and non-imaging applications where (≥¼ λ) • Geometric metric

  6. 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

  7. 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

  8. Point Spread Function • The point spread function captures diffraction effects or the wave • nature of light • Small aberrations (≤ ¼ λ) • Young’s double pin hole experiment • Diffraction metric

  9. Strehl Ratio • Best for small aberrations (≤ ¼ λ)

  10. Geometric vs. Diffraction

  11. 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

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