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function [diam,area,trolands] = PupilDiameterFromLum(lum,source)
% [diam,area,trolands] = PupilDiameterFromLum(lum,[source])
%
% Compute pupil diameter and area from photomic luminance.
% Diameter is in mm, area in mm^2.
% Luminance is in cd/m2.
% Also returns photopic trolands.
%
% Source (string):
% PokornySmith: (default)
% Formula is Eq. 1 from: Pokorny and Smith, "How much light
% reaches the retina", Colour Vision Deficiences XIII (C.
% Cavonius, ed.), pp. 491-511.
%
% DeGrootGebhard:
% Formula is De Groot and Gebhard's from
% Eq. 2(2.4.5) of Wyszecki and Stiles,
% 2cd edition (page 106).
%
% MoonSpencer:
% Formula is Moon and Spencer's from
% Eq. 1(2.4.5) of Wyszecki and Stiles,
% 2cd edition (page 106).
%
% Notes:
% a) The calculations of the DeGroot/Gebhard formula do not seem to agree with the
% same calculations as expressed in Figure 2(2.4.5) on the same page of W+S. One would
% need to go back to the original literature to sort out what is going on.
%
% b) In terms of the different methods, Joel Pokorny (1999, personal communication) says:
% The average pupil diameter/luminance functions in the literature vary enormously.
% This can be seen in the figures in
%
% Moon, P. and D. E. Spencer (1944). "On the Stiles-Crawford Effect."
% Journal of the Optical Society of America 34: 319-329.
%
% and
%
% de Groot, S. G. and J. W. Gebhard (1952). "Pupil size as determined
% by adapting luminance." Journal of the Optical Society of America
% 42: 492-495.
%
% For example, the Reeves (1918, "The visibility of radiation." Transactions of the
% Illuminating Engineering Society 13: 101-109) pupil diameter function is displaced
% roughly 1.5 log units higher on the luminance axis than Crawford's (1936, "The dependence
% of pupil size upon external light stimulus under static and variable conditions."
% Proceedings of the Royal Society B (London) 121(B): 376-395) average data.
%
% Both Moon and Spenser & DeGroot and Gebhard sought functions which were compromises
% between existing data sets. LeGrand's function shows good correspondence with
% the Reeves' data. These three functions nominally describe pupil behavior for binocular
% view of large fields. In vision science we most frequently use fields of limited extent
% and often use monocular view. These stimulus manipulations lead to larger pupils than
% the binocular large field condition. Thus it made sense to me to use the LeGrand function.
% As is mentioned in "How much light..." pupil size varies for all sorts of reasons and any
% estimate should be viewed as having a large tolerance.
%
% 4/2/99 dhb Wrote it.
% 5/8/99 dhb Consolidated different methods.
% 7/8/03 dhb Accept strings without dashes.
% 12/4/07 dhb Added dog case, with a place holder number of 8 mm.
% Set default methods
if (nargin < 2 || isempty(source))
source = 'PokornySmith';
end
% Get diameter according to chosen source
switch (source)
case {'PokornySmith', 'Pokorny_Smith'},
diam = 5 - 3*tanh(0.4*log10(lum));
case {'DegrootGebhard', 'DeGroot_Gebhard'},
diam = 10.^(0.8558-4.01*1e-4*((log10(lum)+8.6).^3));
case {'MoonSpencer', 'Moon_Spencer'},
diam = 4.9 - 3*tanh(0.4*(log10(lum)+1));
case 'PennDog'
diam = 8;
end
% Compute ancillary information
area = pi*(diam/2).^2;
trolands = lum.*area;
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