/usr/share/psychtoolbox-3/PsychCal/SearchGammaTable.m is in psychtoolbox-3-common 3.0.11.20131230.dfsg1-1build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 | function values = SearchGammaTable(targets, input, table)
% values = SearchGammaTable(targets, input, table)
%
% Return the [0-1] entry from the passed table that produces
% output closest to the [0-1] target.
%
% The targets are assumed to be a row vector.
% The table is assumed to be a column vector.
% The returned indices and values are are row vectors.
%
% Works by using Matlab's interp1, with the output as the x values and
% the input as the f(x) values.
%
% I suspect that this is a fast Matlab implementation, but those who want
% to try are welcome to try to do better. (Remember, though, that this
% routine gains in efficiency the more searches are done at once.
% This is because it contains no dreaded loops.)
%
% 4/2/94 dhb Added code that checks for special case of zero output.
% 4/4/94 dhb Fixed code added on 4/2.
% 4/5/94 jms Fixed code added on 4/2.
% 1/21/95 dhb Write search as a loop. Loses time and elegance,
% but prevents allocation of arrays that may be huge.
% 11/16/06 dhb Renamed as SearchGammaTable.
% dhb Start work on converting to [0-1] universe. Change
% name and interface.
% 11/20/06 dhb Finish update by calling through MATLAB's interpolation function.
% 9/15/08 dhb Handle case where there are a bunch of zeros at the beginning of gamma table.
% 5/26/12 dhb Improve comment. This was not doing exhaustive search.
% Check dimensions
[m,n] = size(targets);
if (m ~= 1)
error('Passed targets should be a row vector');
end
[mi,ni] = size(input);
if (ni ~= 1)
error('Passed input should be a column vector');
end
[mt,nt] = size(table);
if (nt ~= 1)
error('Passed table should be a column vector');
end
if (mi ~= mt || ni ~= nt)
error('Input and table must be the same size');
end
% Handle problem that for some monitors, the output is 0 for
% input values up to some threshold. This causes interp1
% to crash. We handle this by getting rid of the intermediate
% zeros from the input, if they are there. This choice means
% that when we ask for 0 out, we get 0 as the answer.
index = find(table == 0);
index1 = find(table ~= 0);
if ~isempty(index)
table = table([index(1) ; index1]);
input = input([index(1) ; index1]);
end
% Invert via linearly interpolation of the passed table
values = interp1(table, input, targets', 'linear')';
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