Lec 14: IQ Flashcards
Metrics to Define Image Quality
Visual Acuity
PSF (point spread fxn)
Wavefront RMS
OTF (including MTF and PTF) Strehl Ratio
The ______ is the image that an optical system forms of a point source.
PSF
The _________ is the most fundamental object, and forms the basis for any complex object.
Point source
The PSF for a perfect optical system is the _______, which is the Fraunhofer diffraction pattern for a circular pupil.
airy disk
how does diffraction affect the retinal image?
For practical reasons, imaging systems are unable to collect the entire wavefront emitted from an object. For the eye, only a section passes through the pupil with the iris representing an obstruction that deviates the light.
This deviation blurs the image.
The image blur size for a point object = 1.22 λ f / d.
Rayleigh Criterion
Two points are resolved at the Rayleigh resolution limit when the peak of the Airy disc from one point is above the first minimum of the other.
is a complex function that measures the loss in contrast in the image of a sinusoidal target, as well as any phase shifts
OTF
the amplitude (i.e. MTF = |OTF|) and the Phase Transfer Function (PTF) is the phase portion of the OTF.
MTF
measures the loss in contrast in the image of a sinusoidal target. It is the ratio of the image contrast and the object contrast.
MTF
is the reciprocal of the minimum value of C that is detectable.
contrast sensitivity (CS)
Its units are the ratio of image contrast over the object contrast as a function of spatial frequency.
MTF
• It is the optical contribution to the contrast sensitivity function (CSF).
MTF
increase spatial frequency (details), decrease what?
MTF
the number of cycles subtending 1 degree
spatial frequency
20/20 letter represents how many cycles/deg?
30 cycles/degree
