Definition of Contrast

Fourier Analysis

• Square wave = Sum of sine waves• Square wave = Fundamental sine wave +

harmonics• Fundamental sine wave is a wave with the

same frequency as the square wave• Third harmonic is a sine wave with 3 times the

square wave• Fifth harmonic is a sine wave with 5 times the

frequency of the square wave

Modulation Transfer Function

• Object Contrast-> Lens -> Image contrast

• MTF = Image Contrast/ Object Contrast

• MTF = 1.0 for an ideal lens (or system)MTF is determined by frequency to obtain a

graph.

Modulation Transfer Function (MTF)Frequency Object Contrast Image Contrast MTF

2 10 8 0.805 9 7.5 0.838 8.7 6.3 0.72

10 7.5 5.2 0.6915 6.3 3.8 0.6018 5.2 2.1 0.4025 4.2 1.5 0.3630 4 0.9 0.2340 4 0.7 0.1850 3.8 0.4 0.1160 3.6 0.33 0.09

Contrast Sensitivity Function(CSF)

Ganglion cellReceptiveField

Ganglion cell receptive field

Ganglion cell receptive field

Ganglion cell response to diffuse illumination

Ganglion cell response to spatial grating

Mach bandsDark band Bright band

Mach bands

Recognition Acuity

• Snellen• HOTV• LEA• Patti Pics

LEA Symbols

Patti Pics

HOTV Test

Resolution Acuity

• Tumbling E• Landolt C• Broken Wheel

Broken Wheel test

Tumbling E

Landolt C

Minimum detectable acuity

Hyperacuity

• Vernier• Alignment test• Tilt test