1. 3: The Photoreceptor Mosaic
Human Perception
3: The Photoreceptor Mosaic

2. The Photoreceptor Types
Spatial Distribution of Receptors
3.2

3. The Photoreceptor Types
Spatial Distribution of Receptors
3.3

4. The Photoreceptor Types
Schematics
3.4

5. The Photoreceptor Types
Receptor drawings
3.5

6. The Photoreceptor Types
Cone wavelength absorptions
3.6

7. The Photoreceptor Types
Curcio et al, 1990
3.7

8. The S-cone Mosaic
Psychophysical estimation of S-cone mosaic: Williams, Macleod and Hayhoe experiments, 1981
3.8

9. The S-cone Mosaic
A biological estimate of the S-code spatial mosaic, DeMonasterio et al, 1985, just outside the fovea
3.9

10. The S-cone Mosaic: Near Periphery
A biological estimate of the S-code spatial mosaic, near periphery
3.10

11. Calculating the Viewing Angle
tan(φ)=0.0025mm/17mm=
i.e degrees or 0.5 minutes or 30 seconds
3.11

12. Sampling and Aliasing
Aliasing of signals results when sampled values are the same but in-between values are not
3.12

13. Sampling and Aliasing Harmonic undersampled all = 1:16; n = all/16;
freq = 15;
f = cos(2*pi*freq*n);
plot(n,f,'b-o’);hold on
all = 1:256;
n = all/256;
plot(n,f,'r-')
3.13

14. Sampling and Aliasing Harmonic oddly sampled clf all = 1:16;
n = all/16;
freq = 11.2;
f = cos(2*pi*freq*n);
plot(n,f,'b-o')
hold on
all = 1:256;
n = all/256;
freq = 15;
plot(n,f,'r-')
3.14

15. Sampling and Aliasing F = N/2 cos(2π(N/2+f) i/N)= cos(2π(N/2-f)i/N )
Square-wave (two dimensional) aliasing
Nyquist frequency
F = N/2
cos(2π(N/2+f) i/N)=
cos(2π(N/2-f)i/N )
3.15

16. The L- and M-Cone Mosaic
Perceived aliasing patterns
Consistent with Nyquist frequency of 60cpd
3.16

17. The L- and M-Cone Mosaic
Foveal mosaic
no S-cones nor rods
3.17

18. The L- and M-Cone Mosaic
Cone receptor mosaic, Roorda and Williams, 1999
all three type of cones visible, L(red), M(green), S(blue)
3.18