filt_get_c_layer.m

Standard model object recognition matlab code

function f = filt_get_C_layer (prev_layer,varargin)

% FUNCTION f = filt_get_C_layer (prev_layer,varargin)
% 
% Create a typical C-layer filter, whose size is determined by the
% size of the previous layer.  The first arguement can be given as
% a structure (of previous layer's responses) or as 3xnum_scale
% matrix, specifying the sizes (x,y,features) by number of scales.
% It will, in turn, invoke get_sized function to build the filters
% of ones.  
% The varargin{1} may specify the shift values for each scale.  The
% default value is 1, for shift.

f = [];

% Get sizes
if isstruct(prev_layer)
  num_scale = length(fieldnames(prev_layer));
  for i = 1:num_scale
    scale_tag  = ['s' num2str(i)];
    layer_size(:,i) = size(getfield(prev_layer,scale_tag));
  end
else % The input arguement prev_layer is the size.
  num_scale  = size(prev_layer,2);
  layer_size = prev_layer;
  if size(prev_layer,1) ~= 3
    error('Size was not specified correctly.');
  end
end

% Get shifts
if length(varargin) > 0
  shifts = varargin{1};
  if length(shifts) ~= num_scale
    disp('Parameter shifts is not well defined.  Use 1.');
    shifts = ones(num_scale,1);
  end
else % no other input
  shifts = ones(num_scale,1);
end

% Now compute the C-layer filters.
for i = 1:num_scale
  scale_tag  = ['s' num2str(i)];
  f = filt_get_sized(f,layer_size(:,i)',shifts(i),scale_tag);
  % It is a memory waste to copy 1's into different scales, so here for
  % higher scales 's2' and beyond, save [].
  if i > 1
     f = setfield(f, ['f1_' scale_tag], []);
     f = setfield(f, ['f2_' scale_tag], []);
     f = setfield(f, ['i1_' scale_tag], []);
     f = setfield(f, ['i2_' scale_tag], []);
     f = setfield(f, ['i3_' scale_tag], []);     
  end
  
end