warpH.m

function warp_im = warpH(im, H, out_size, fill_value)
% warpH projective image warping
%   warp_im=warpA(im, A, out_size)
%   Warps a size (w,h,channels) image im using the  (3,3) homography H
%   producing an (out_size(1),out_size(2)) output image warp_im
%
%   The pixels of warp_im are sampled at (x,y) coordinates 
%   (1,1)-(out_size(2),out_size(1))
%
%   The coordinates of the pixels in the source image 
%   are taken to be  $(1,1)-(size(im,2), size(im,1)) and 
%   are transformed according to:
%   warped_coords := H*source_coords
%
%   warp_im=warpA(im, A, out_size,fill_value)
%   Uses fill_value (scalar) to paint empty regions.



if ~exist('fill_value', 'var') || isempty(fill_value)
    fill_value = 0;
end

tform = maketform('projective', H'); 
warp_im = imtransform(im, tform, 'bilinear', 'XData', [1 out_size(2)], 'YData', [1 out_size(1)], 'Size', out_size(1:2), 'FillValues', fill_value*ones(size(im,3),1));