function AF = agefact(age, D)
%agefact(age) Calculates Ijspeert's age factor (AF) given age in years
%	and doubling age (D). If not specified D is set at the default 70 years,
% 	based on Ijspeert's equations.
% 

function B1 = B1calc (p, AF)
%B1calc(p, AF)	Calculates B1, an essential constant in determining how 
% 	the pointspread function is effected by pupil size. Input variables 
%	are as follows:
% 
%p = pupil size in mm
%AF = age factor (calculated with agefact)
%
%Output value is in c/rad^-1

%B2calc(p, AF)	Calculates B2, an essential constant in determining how 
% 	the pointspread function is effected by pupil size. Input variables 
%	are as follows:
% 
%p = pupil size in mm
%AF = age factor (calculated with agefact)
%
%Output value is in c/rad^-1

function B3 = B3calc(AF, m)
%B3calc(AF, m)	Calculates B3, an essential constant in determining how 
% 	the pointspread function is effected by eye pigmentation. Input variables 
%	are as follows:
%
%AF = age factor (calculated with agefact)
%m = pigmentation factor.
%
%Note that this function can be used with the pigment function to obtain a 
%default m value.
%Usage: B3calc(AF, pigment);
%
%(From Ijspeert, et al. 1992.)

function b = bcalc(AF)
%bcalc(AF)	calculates a constant used in determining the B1 and B2 variables.
%
%AF = agefactor = agefact(age)  (age in years)
%
%From Ijspeert, 1992.
%
%SEE: B1calc, B2calc, agefact.

function c1 = c1calc(AF, p, m)
%c1calc(AF, p, m) Calculates c1, a value used in the calculation 
%of the pointspread function (PSF) and the modulation transfer function (MTF). 
%C1 aids in the modeling of the PSF and MTF dependence on pupil size.
%
%AF = age factor
%p = pupil size in mm
%m = pigmentation parameter
%
%Based on the modelings of Ijspeert et al, 1992.
%
%SEE: c2calc, cshort

function c2 = c2calc(AF, p, m)
%c2calc(AF, p, m) Calculates c2, a value used in the calculation 
%of the pointspread function (PSF) and the modulation transfer function (MTF). 
%C2 aids in the modeling of the PSF and MTF dependence on pupil size.
%
%AF = age factor
%p = pupil size in mm
%m = pigmentation parameter
%
%Based on the modelings of Ijspeert et al, 1992.
%
%SEE: c1calc, cshort

function c3 = c3calc(AF, m)
%c3calc(AF, m) Calculates c3, a value used in the calculation 
%of the pointspread function (PSF) and the modulation transfer function (MTF). 
%C3 aids in the modeling of the PSF and MTF dependence on pigmentation.
%
%AF = age factor
%m = pigmentation parameter
%
%Based on the modelings of Ijspeert et al, 1992.
%
%SEE: c4calc, clong, agefact

function c4 = c4calc(AF, m)
%c4calc(AF, m) Calculates c4, a value used in the calculation 
%of the pointspread function (PSF) and the modulation transfer function (MTF). 
%C4 aids in the modeling of the PSF and MTF dependence on pigmentation.
%
%AF = age factor
%m = pigmentation parameter
%
%Based on the modelings of Ijspeert et al, 1992.
%
%SEE: c3calc, clong, agefact

function cla = clong(AF, m)
%clong(AF, m)	Determines c for the long angle factors
%
%AF = age factor = agefact(age)
%m = pigmentation parameter (see pigment)
%
%Based on Ijspeert, et al. 1992.
%
%SEE: c3calc, c4calc, cshort

function csa = cshort(AF, m)
%cshort(AF, m)	Determines c for the short angle factors
%
%AF = age factor = agefact(age)
%m = pigmentation parameter (see pigment)
%
%Based on Ijspeert, et al. 1992.
%
%SEE: c1calc, c2calc, clong

function rad = deg2rad(deg)
%deg2rad(deg)	converts degrees to radians
%Input variable:
%deg = degree value

function e = ecalc(AF)
%ecalc(AF)	calculates a constant used in determining the B1 and B2 variables.
%
%AF = agefactor = agefact(age)  (age in years)
%
%From Ijspeert, 1992.
%
%SEE: B1calc, B2calc, agefact

function Fbi = funBi(i, phi, p, AF, m)
%funBi(i, phi, p, AF, m)	calculates Fbi for the PSFip calculations
%
%
%Input variables:
%i = which out of four B to use
%phi = angle (degrees)
%p = pupil diameter (mm)
%AF = age factor = agefact(age)
%m = pigmentation parameter
%
%SEE PSFip, B1calc, B2calc, B3calc, B4calc
%

%lbi(i, phi, p, AF, m)	Intermediate value in the calculation of the Linespread 
% function.
%

function LSF = LSFip(phi, age, p, m)
%LSFip(phi, age, p, m)	Calculates the linespread function (LSF) based on the 
%	equations espoused by Ijspeert et al. The user must specify the angle,
%	phi, in degrees. All other values are optional, and will be set at the 
%	following defaults if not specified:
%
%	age = age of subject in years 	Default age = 0 years	
%	p = pupil diameter in mm 		Default value = 4 mm.
%	m = pigmentation parameter		Default = call to pigment function
%

function Mb = Mbcalc(i, q, AF, p, m)
%Mbcalc(i, q, p, AF, m) Calculates Mb, an intermediate in the calculation of
%	the Modulation transfer function. Modeling based on Ijspeert, 1992.
%	However, this function can be used independently of the MTFip function.
%
%SEE: MTFip

function MTFgraph(maxfreq, age, p)
%MTFgraph(maxfreq, age, p) Graphs a series of MTF functions in order to compare
%them
%

function MTF = MTFip(q, p, age, m)
% MTF = MTFip(q, p, age, m) Calculates the modulation transfer function (MTF)
%	based on data from Ijspeert et al. 1992. All input variables are optional
%	except for q
%
%Input variables:
%	q = frequency in c/deg		
%	p = pupil diameter in mm		Default = 4 mm
%   age = age in years				Default = 0 years
%	m = pigmentation parameter		Default = call to pigment function
%
%SEE rad2deg, deg2rad

function m = pigment
%pigment	sets the pigmentation parameter (m) equal to one of the four 
%	default values, based on mean pigmentations of different groups. The 
%	groups are as follows:
%
%	Caucasian mean.							m = 0.142
%	mean blue-eyed Caucasian				m = 0.160
%	mean brown-eyed Caucasian				m = 0.106
%	mean pigmented-skin dark brown eye		m = 0.056
%
%	Values are from Ijspeert et al, 1992.

%PSFip(phi, age, p, m)	Calculates the pointspread function (PSF) based on the 
%	equations espoused by Ijspeert et al. The user must specify the angle,
%	phi, in degrees. All other values are optional, and will be set at the 
%	following defaults if not specified:
%
%	age = age of subject in years 	Default age = 0 years	
%	p = pupil diameter in mm 		Default value = 4 mm.
%	m = pigmentation parameter		Default = call to pigment function


function PSF = PSFsimp(phi, age)
%PSFsimp A simplified calculation based on the point spread function 
%(PSF) calculations of Ijspeert, 1992.
% phi is in degrees
% pupil = 4 mm
% m = 0.142
% Default age is 0 years

function deg = rad2deg(rad)
%rad2deg(rad)	converts radians to degrees
%Input Variable:
%rad = radian value