Outils pour utilisateurs

Outils du site


homography

The Homography model

Compute an image given an original image and the homography between the 2 image planes

CalculeImageHomographie.m
 function imout=CalculeImageHomographie(H,imout,hautout,largout,imin,hautin,largin)
%fonction imout=CalculeImageHomographie(H,imout,hautout,largout,imin,hautin,largin)
%@Bertrand VANDEPORTAELE
%La fonction calcule l'image imout à partir de l'image imin
%H= homographie entre les 2 images tel que imout= H*imin
%imout= image de sortie, elle est aussi en entrée, car on peut la modifier
%hautout,largout= dimensions de l'image de sortie
%imin= image d'entrée
%hautin,largin= dimensions de l'image d'entrée
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
for y=1:hautout
    for x=1:largout
        p2=H*[x,y,1]'; %transformation homographique inverse
        ud=round(p2(1)/p2(3));
        vd=round(p2(2)/p2(3));
        ud;
        vd;
        if vd>0 & ud>0 & vd<=hautin & ud<=largin
            %ca tombe dans l'image
            val=imin(vd,ud);
            imout(y,x)=val; %on attribue la couleur du pixel concerné
        else
            %ca tombe hors de l'image datamatrix, on laisse la valeur du
            %fond
            %eventuellement, on aurait pu faire:
%            imout(y,x)=255; %on attribue la couleur blanche
        end
    end
end 

Estimation of Homography from 2D points correspondances using the DLT algorithm

compute2DHomographyUsingDLT.m
function [ H] = compute2DHomographyUsingDLT( p1,p2)
%B. Vandeportaele
%compute the Homography H using the DLT Algorithm for 4 2D points 
%correspondences such as : p2=H.p1
u11=p1(1,1);u12=p1(1,2);
u13=p1(1,3);u14=p1(1,4);
v11=p1(2,1);v12=p1(2,2);
v13=p1(2,3);v14=p1(2,4);
 
u21=p2(1,1);u22=p2(1,2);
u23=p2(1,3);u24=p2(1,4);
v21=p2(2,1);v22=p2(2,2);
v23=p2(2,3);v24=p2(2,4);
 
A=[ -u11, -v11, -1,    0,    0,  0, u11*u21, u21*v11;
    0,    0,  0, -u11, -v11, -1, u11*v21, v21*v11;
    -u12, -v12, -1,    0,    0,  0, u12*u22, u22*v12;
    0,    0,  0, -u12, -v12, -1, u12*v22, v22*v12;
    -u13, -v13, -1,    0,    0,  0, u13*u23, u23*v13;
    0,    0,  0, -u13, -v13, -1, u13*v23, v23*v13;
    -u14, -v14, -1,    0,    0,  0, u14*u24, u24*v14;
    0,    0,  0, -u14, -v14, -1, u14*v24, v24*v14];
B =[ -u21; -v21; -u22; -v22; -u23; -v23; -u24; -v24];
%solve A*Hv=B
Hv=inv(A)*B;
%reconstruct the homography matrix from the vector solution
H=[Hv(1:3)';Hv(4:6)';Hv(7:8)',1];
end

Checking the obtained results

check2DHomography.m
function [ err] = check2DHomography(H, p1,p2 )
%B. Vandeportaele
%compute the error in R2 (after deshomogeneisation) for every points 
%contained in p1 and p2 matrices considering the homography H
%err= p2 -deshomogenieisation(H.p1)
err=[];
for i=1:size(p1,2)
    u11=p1(1,i);
    v11=p1(2,i);
    wuv21p=H*[u11;v11;1];
    err(1,i)=p2(1,i)-(wuv21p(1)/wuv21p(3));
    err(2,i)=p2(2,i)-(wuv21p(2)/wuv21p(3));
end
end

Normalization of the data for least squares fitting

normalizeForH.m
function [ p2, s,tx,ty] = normalizeForH( p1 )
%B. Vandeportaele
%normalization of the data for homography estimation. Scale s and 
%translation (tx,ty) is computed to obtain a distribution of point with 0 
%mean and sqrt(2) std dev.
%as explained in Geometry in Computer Vision (2ed,OUP,2003)(T)(672s)
% Data Normalization p107 & p180
 
%transform p1 points to p2 such that p2 points are centered around 0:0 and mean distance to 0:0 is sqrt(2)
 
%eventually see page 128 for the case where some points in p1 are very far away from the origin
%it would require a complete homography instead of just a scaling and
%translation, as it involve dealing with p1 in projective space P2
 
%in page 109, it is explained that non isotropic scaling is not necessary.
 
 
%average distance
m=mean(p1,2)';
 
%p1-[m(1)*ones(1,size(p1,2));    m(2)*ones(1,size(p1,2))]
%translation to bring the centroid at 0:0
dist=[];
for i=1:size(p1,2)
    pc(1:2,i)=p1(:,i)-m'; %centered points
    dist(i)=norm(pc(1:2,i),2);
end
meandist=mean(dist)
s=sqrt(2)/meandist;
 
for i=1:size(p1,2)
    p2(1:2,i)=s*pc(:,i); %scaled and centered points
end
tx=-s*m(1);
ty=-s*m(2);
 
end

Uncertainty propagation

jaco.m
%B. Vandeportaele
%script to achieve symbolic computation of the jacobian
% du2/dHij
% dv2/dHij
% Hij being the coefficients of the homography such as
% w.u2       u1
% w.v2 = H . v1
%   w.        1
clear all
 
param=1
 
h11=sym('h11','real');h12=sym('h12','real');h13=sym('h13','real');
h21=sym('h21','real');h22=sym('h22','real');h23=sym('h23','real');
h31=sym('h31','real');h32=sym('h32','real');h33=sym('h33','real');
%possibly use 2 parameterization for the homography, h33 may be set to 1
if param==0
    H=[h11 h12 h13; h21 h22 h23;h31 h32 h33]
else
    H=[h11 h12 h13; h21 h22 h23;h31 h32 1]
end
 
u1=sym('u1','real');
v1=sym('v1','real');
 
P1=[u1;v1;1];
%apply the homography
P2=H*P1
%deshomogeneization
u2=P2(1,:)/P2(3,:)
v2=P2(2,:)/P2(3,:)
%compute the jacobians
if param==0
    J=jacobian ([u2, v2], [h11, h12, h13, h21, h22, h23, h31, h32, h33])
else
    J=jacobian ([u2, v2], [h11, h12, h13, h21, h22, h23, h31, h32])
end

Conclusion for param=1: $J= \left(\begin{array}{cccccccc} \frac{\mathrm{u1}}{\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1} & \frac{\mathrm{v1}}{\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1} & 0 & 0 & 0 & -\frac{\mathrm{u1}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u1} + \mathrm{h12}\, \mathrm{v1}\right)}{{\left(\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1\right)}^2} & -\frac{\mathrm{v1}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u1} + \mathrm{h12}\, \mathrm{v1}\right)}{{\left(\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1\right)}^2}\\ 0 & 0 & 0 & \frac{\mathrm{u1}}{\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1} & \frac{\mathrm{v1}}{\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1} & -\frac{\mathrm{u1}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u1} + \mathrm{h22}\, \mathrm{v1}\right)}{{\left(\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1\right)}^2} & -\frac{\mathrm{v1}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u1} + \mathrm{h22}\, \mathrm{v1}\right)}{{\left(\mathrm{h31}\, \mathrm{u1} + \mathrm{h32}\, \mathrm{v1} + 1\right)}^2} \end{array}\right)$

usejaco3.m
%B. Vandeportaele
%script to illustrate uncertainty propagation for homography (projective
%transformation)
 
clear all
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%define 4 set of 2 2D points correspondances such as
% w.u21       u11
% w.v21 = H . v11
%   w.         1
%   position u11,v11 in plane 1 is supposed to be perfectly known
u11=0;v11=0;
u12=1;v12=0;
u13=0;v13=1;
u14=1;v14=1;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%position u21,v21 in plane 2 is associated with a covariance matrix
u21=10;v21=10;
u22=150;v22=40;
u23=30;v23=130;
u24=190;v24=210;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%covariance for the point's positions in plane 2.  std dev are square roots
%of the diagonal values
%default value:
Cp=1*eye(8)
%change the value as needed if uncertainty are not the same for all the
%points
if 1
    Cp(1,1)=3;
    Cp(2,2)=5;
    Cp(3,3)=10;
    Cp(4,4)=25;
    Cp(5,5)=50;
    Cp(6,6)=1;
    Cp(7,7)=0.1;
    Cp(8,8)=0.1;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%store coordinates in matrices
p1=[u11,u12,u13,u14;v11,v12,v13,v14]
p2=[u21,u22,u23,u24;v21,v22,v23,v24]
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%DLT Algorithm:
[ H] = compute2DHomographyUsingDLT( p1,p2)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%check computed H, should be 0
[ err] = check2DHomography(H, p1,p2 )
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
h11=H(1,1);h12=H(1,2);h13=H(1,3);
h21=H(2,1);h22=H(2,2);h23=H(2,3);
h31=H(3,1);h32=H(3,2);h33=H(3,3);
%compute J numerically then invert the 8x8 matrix to obtain Ji
J =[];
% computed in jaco.m:   J=jacobian ([u2, v2], [h11, h12, h13, h21, h22, h23, h31, h32])
for i=1:4
    u1=p1(1,i);v1=p1(2,i);
    J=[J;
        u1/(h31*u1 + h32*v1 + 1), v1/(h31*u1 + h32*v1 + 1), 1/(h31*u1 + h32*v1 + 1),                        0,                        0,                       0, -(u1*(h13 + h11*u1 + h12*v1))/(h31*u1 + h32*v1 + 1)^2, -(v1*(h13 + h11*u1 + h12*v1))/(h31*u1 + h32*v1 + 1)^2;
        0,                        0,                       0, u1/(h31*u1 + h32*v1 + 1), v1/(h31*u1 + h32*v1 + 1), 1/(h31*u1 + h32*v1 + 1), -(u1*(h23 + h21*u1 + h22*v1))/(h31*u1 + h32*v1 + 1)^2, -(v1*(h23 + h21*u1 + h22*v1))/(h31*u1 + h32*v1 + 1)^2];
end
J
detJ=det(J)
%check if detJ is high enough, otherwise it won't be invertible in
%practice
if detJ<0.01
    display 'the system looks ill-conditionned'
    return;
end
Ji=inv(J)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 
% In case we want to estimate H from more than 4 correspondances, get from:
% http://stackoverflow.com/questions/30737382/getting-covariance-matrix-when-using-levenberg-marquardt-lsqcurvefit-in-matlab
% I think I have solved this myself but will post how here if anyone else is having the same trouble.
% The covariance matrix can be calculated from the Jacobian by:
% C = inv(J'*J)*MSE
% Where MSE is mean-square error:
% MSE = (R'*R)/(N-p)
% Where R = residuals, N = number of observations, p = number of coefficients estimated.
% Or MSE can be calculated via iteration.
% Hopefully this will help someone else in the future.
% If anyone spots error please let me know. Thanks
 
 
%QUESTION????? in that case what is the inverse of the (non square) jacobian for  the inverse homography H^-1
 
 
%propagation of thee covariance to the coefficients of H
Ch=Ji*Cp*Ji'
 
detCh=det(Ch) %what is the meaning of that value: look at
%https://math.stackexchange.com/questions/889425/what-does-determinant-of-covariance-matrix-give
 
%compute the covariance on the coefficients of the 2D points, it should give
%the same value than Cp
Cp2=J*Ch*J'
ErrorCp=Cp-Cp2
 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%Plot the uncertainty on a grid sampled in plane 1
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
close all
figure
hold on
axis equal
for u15=-2:.25:2;
    for v15=-2:.25:2;
        wuv25=H*[u15;v15;1];
        u25=wuv25(1)/wuv25(3);
        v25=wuv25(2)/wuv25(3);
        Jp=[ u15/(h31*u15 + h32*v15 + 1), v15/(h31*u15 + h32*v15 + 1), 1/(h31*u15 + h32*v15 + 1),                        0,                        0,                       0, -(u15*(h13 + h11*u15 + h12*v15))/(h31*u15 + h32*v15 + 1)^2, -(v15*(h13 + h11*u15 + h12*v15))/(h31*u15 + h32*v15 + 1)^2;
            0,                        0,                       0, u15/(h31*u15 + h32*v15 + 1), v15/(h31*u15 + h32*v15 + 1), 1/(h31*u15 + h32*v15 + 1), -(u15*(h23 + h21*u15 + h22*v15))/(h31*u15 + h32*v15 + 1)^2, -(v15*(h23 + h21*u15 + h22*v15))/(h31*u15 + h32*v15 + 1)^2];
        Cp5=Jp*Ch*Jp';
        plotcovar(u25,v25,Cp5,'r+','b-');
    end
end
%plot the covariance for the four 2D point correspondances used by DLT
for i=1:4
    u2=p2(1,i);v2=p2(2,i);
    Cpi=Cp(1+(i-1)*2:2+(i-1)*2,1+(i-1)*2:2+(i-1)*2);
    plotcovar(u2,v2,Cpi,'g+','g-');
end   
 
%en vert, 4 points (et leur incertitude) utilisés pour estimer l'homographie par Direct Linear Transform
%en rouge, des points auquel on applique l'homographie calculée (interpolation et extrapolation)
%et en bleu l'incertitude de l'homographie estimé propagée à ces points

Function to plot the covariance

plotcovar.m
function plotcovar(u,v,C,m1,m2)
%get from http://www.visiondummy.com/2014/04/draw-error-ellipse-representing-covariance-matrix/
% Get the 95% confidence interval error ellipse
chisquare_val = 2.4477;
%INFO: pour une covariance=identité, trace un cercle de RAYON chisquare_val
%pour une covariance diagonale, les termes de variance sont les carrés des écarts type
%l'ellipse tracée un aura ses DEMI-axes de longeur ecart type * chisquare_val
 
 
 
%hold on
%plotcovar(10,20,[2,4;3,1],'r+','b-');
%plotcovar(10,20,[1,0;0,1],'r+','b-');
 
plot(u,v,m1)
 
%bvdp, added step to inforce that C is symetric 
%if this precaution is not taken, this kind of matrix can be provided 
%C=[0.999999999999951 2.73114864057789e-14;-1.50990331349021e-14 0.999999999999964]
%and it will result in complex eigen value, which won't be treatable by the
%atan2 function used later...
Cm=(C(2,1)+C(1,2))/2;
C(2,1)=Cm;
C(1,2)=Cm;
 
 
% Calculate the eigenvectors and eigenvalues
covariance =C;
[eigenvec, eigenval ] = eig(covariance);
[eigenvec, eigenval ] = eig(covariance,'nobalance');
 
% Get the index of the largest eigenvector
[largest_eigenvec_ind_c, r] = find(eigenval == max(max(eigenval)));
largest_eigenvec = eigenvec(:, largest_eigenvec_ind_c);
 
% Get the largest eigenvalue
largest_eigenval = max(max(eigenval));
 
% Get the smallest eigenvector and eigenvalue
if(largest_eigenvec_ind_c == 1)
    smallest_eigenval = max(eigenval(:,2));
    smallest_eigenvec = eigenvec(:,2);
else
    smallest_eigenval = max(eigenval(:,1));
    smallest_eigenvec = eigenvec(1,:);
end
 
% Calculate the angle scriptshellbetween the x-axis and the largest eigenvector
angle = atan2(largest_eigenvec(2), largest_eigenvec(1));
 
% This angle is between -pi and pi.
% Let's shift it such that the angle is between 0 and 2pi
if(angle < 0)
    angle = angle + 2*pi;
end
 
% Get the coordinates of the data mean
avg = [u;v]; %mean(data);
 
theta_grid = linspace(0,2*pi);
phi = angle;
X0=avg(1);
Y0=avg(2);
a=chisquare_val*sqrt(largest_eigenval);
b=chisquare_val*sqrt(smallest_eigenval);
 
% the ellipse in x and y coordinates 
ellipse_x_r  = a*cos( theta_grid );
ellipse_y_r  = b*sin( theta_grid );
 
%Define a rotation matrix
R = [ cos(phi) sin(phi); -sin(phi) cos(phi) ];
 
%let's rotate the ellipse to some angle phi
r_ellipse = [ellipse_x_r;ellipse_y_r]' * R;
 
% Draw the error ellipse
plot(r_ellipse(:,1) + X0,r_ellipse(:,2) + Y0,m2)
%hold on;
 
% Plot the original data
%plot(data(:,1), data(:,2), '.');
%mindata = min(min(data));
%maxdata = max(max(data));
%Xlim([mindata-3, maxdata+3]);
%Ylim([mindata-3, maxdata+3]);
%hold on;
 
% Plot the eigenvectors
%quiver(X0, Y0, largest_eigenvec(1)*sqrt(largest_eigenval), largest_eigenvec(2)*sqrt(largest_eigenval), '-m', 'LineWidth',2);
%quiver(X0, Y0, smallest_eigenvec(1)*sqrt(smallest_eigenval), smallest_eigenvec(2)*sqrt(smallest_eigenval), '-g', 'LineWidth',2);
%hold on;
 
% Set the axis labels
%hXLabel = xlabel('x');
%hYLabel = ylabel('y');

Results

Bi-cubic interpolation of Homographies

bilinearInterpolationMulti.m
function val = bilinearInterpolationMulti(x, y, A)
%B. Vandeportaele
[haut,larg,nbchannels]=size(A);
%preallocate the return value
val=zeros(nbchannels,1);
u=x;
v=y;
fu= floor(x);
fv = floor(y);
A1=(fv+1-v)*(fu+1-u);
A2=(fv+1-v)*(u-fu);
A3=(v-fv)*(fu+1-u);
A4=(v-fv)*(u-fu);
%if ( (fu>=0) && (fu<larg-2) && (fv>=0) && (fv<haut-2))
if ( (fu>=1) && (fu<larg-1) && (fv>=1) && (fv<haut-1))
    %close enough from the boundaries
    for n=1:nbchannels
        val(n)= A1*A(fv,fu,n) ...
            +A2*A(fv,fu+1,n) ...
            +A3*A(fv+1,fu,n) ...
            +A4*A(fv+1,fu+1,n);
    end
else
    %too close from the boundaries, don't interpolate
end
bicubicInterpolationMulti.m
function val = bicubicInterpolationMulti(x, y, data)
%B. Vandeportaele
%https://en.wikipedia.org/wiki/Bicubic_interpolation
%https://fr.wikipedia.org/wiki/Interpolation_bicubique
%A is a k.l.m matrix, m being the number of channels
nbchannels=size(data,3);
%preallocate the return value
val=zeros(nbchannels,1);
%Control points
x0 = floor(x);
y0 = floor(y);
x_1 = x0-1;
x1 = x0+1;
x2 = x0+2;
y_1 = y0-1;
y1 = y0+1;
y2 = y0+2;
 
for n=1:nbchannels
    % Function evaluated at control points
    f_1_1 = data(y_1,x_1,n);
    f_10 = data(y0,x_1,n);
    f_11 = data(y1,x_1,n);
    f_12 = data(y2,x_1,n);
    f0_1 = data(y_1,x0,n);
    f00 = data(y0,x0,n);
    f01 = data(y1, x0,n);
    f02 = data(y2, x0,n);
    f1_1 = data(y_1, x1,n);
    f10 = data(y0, x1,n);
    f11 = data(y1, x1,n);
    f12 = data(y2, x1,n);
    f2_1 = data(y_1, x2,n);
    f20 = data(y0, x2,n);
    f21 = data(y1, x2,n);
    f22 = data(y2, x2,n);
 
    % Derivatives in x evaluated at control points
    fx0_1 = (f1_1 - f_1_1)/2;
    fx00 = (f10 - f_10)/2;
    fx01 = (f11 - f_11)/2;
    fx02 = (f12 - f_12)/2;
    fx1_1 = (f2_1 - f0_1)/2;
    fx10 = (f20 - f00)/2;
    fx11 = (f21 - f01)/2;
    fx12 = (f22 - f02)/2;
 
    % Derivatives in y evaluated at control points
    fy00 = (f01 - f0_1)/2;
    fy10 = (f11 - f1_1)/2;
    fy01 = (f02 - f00)/2;
    fy11 = (f12 - f10)/2;
 
    % Derivatives in x and y evaluated at control points
    fxy00 = (fx01 - fx0_1)/2;
    fxy10 = (fx11 - fx1_1)/2;
    fxy01 = (fx02 - fx00)/2;
    fxy11 = (fx12 - fx10)/2;
 
    % Interpolation
    Px=[1,(x-x0),(x-x0)^2,(x-x0)^3];
    %don't know why but sometime the generated Px is a column vector
    Px=reshape(Px,1,4);
    Py=[1;(y-y0);(y-y0)^2;(y-y0)^3];
 
    A=[ 1  0  0  0; ... Coefficients aij
        0  0  1  0; ...
        -3  3 -2 -1; ...
        2 -2  1  1];
    F=[ f00  f01  fy00  fy01; ...
        f10  f11  fy10  fy11; ...
        fx00 fx01 fxy00 fxy01; ...
        fx10 fx11 fxy10 fxy11];
    val(n)=Px*A*F*A'*Py;
end
saveRawFloat.m
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% saveRawFloat save a matlab matrix to a binary file for export.
% Input : - mat : matrix to export in a binary file.
%         - nomfichier : file name of the futur binary file.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function saveRawFloat(mat, nomfichier)
%saveRawFloat(zeros(4), '../tmp/test.raw')
% Compute number of values, we want to save
nb=1;
for i=1:size(size(mat),2)
nb=nb*size(mat,i);
end
% Open the file
fid = fopen(nomfichier, 'wb');
% Save the number of elements
fwrite(fid, nb, 'uint32');    % il faudra verifier l'endianess...
% Transpose matrix to save data line after line.
% Data are saved in simple precision floating point numbers 32 bits.
fwrite(fid, mat', 'float'); 
fclose (fid);
HomographyInterpolation.m
%B. Vandeportaele October 2017
%Cubic spline interpolation in Homography space for deflectometry
close all
clear all
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%set the size of the spline control point grid
sx=15;
sy=10;
 %how many sampled pixels between 2 control points in each direction for
 %the generation of the image
samplingfactor=100;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%choose the type of interpolation for homography coefficients through
%function pointer
InterpolationFunction=@bicubicInterpolationMulti;
%InterpolationFunction=@bilinearInterpolationMulti;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
HomographyGrid=zeros(sy,sx,9);
%identity matrix by default
HomographyDefault=reshape(eye(3),9,1);
%if the default value has to be set differently
%HomographyDefault=reshape([1,0,65; 0,1,0; 0,0,1],9,1);
%fill the grid with the default value
for y=1:sy
    for x=1:sx
        HomographyGrid(y,x,:)=HomographyDefault;
    end
end
%perturbate some control points of the spline
HomographyGrid(5,4,:)=reshape([1,0,0; 0,1,0; 0,0,0.9],9,1);
HomographyGrid(4,4,:)=reshape([1.3,0,0; 0,1.3,0;   0,0,1],9,1);
% HomographyGrid(5,4,:)=reshape([1,0,0; 0,1,0; 0,0,0.22],9,1);
% HomographyGrid(5,5,:)=reshape([1,0,0; 0,1,0; 0,0,1.3],9,1);
% HomographyGrid(6,5,:)=reshape([1,0,0; 0,1,0; 0,0,1.5],9,1);
% HomographyGrid(6,4,:)=reshape([1,0,0; 0,1,0; 0,0,0.3],9,1);
% HomographyGrid(6,4,:)=reshape([1.2,0,0; 0,0.9,0; 0,0,1],9,1);
HomographyGrid(6,5,:)=reshape([1,0,0; 0,1,0;   0,0,1],9,1);
HomographyGrid(6,8,:)=reshape([1,0,60; 0,1,-30; 0,0,1],9,1);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%interpolate the homography in a small region at low resolution for
%visualization purpose
%very unefficient code because the size of the destination matrix are not
%known at the begining=> reallocation
indy=1;
for yy=3:0.1:sy-2
    indx=1;
    for xx=3:0.1:sx-2
        %val = InterpolationFunction(  xx,yy,HomographyGrid);
        val = feval(InterpolationFunction, xx,yy,HomographyGrid);
        indx=indx+1;
        res(indy,indx,1)=xx;
        res(indy,indx,2)=yy;
        res(indy,indx,3)=val(9);
        InterpolatedFunction(indy,indx,:)=val;
    end
    indy=indy+1;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure
axis equal
plot3(res(:,:,1),res(:,:,2),res(:,:,3),'r+')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure
for channel=1:9
    subplot(3,3,channel)
    imagesc(InterpolatedFunction(:,:,channel))
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%compute correspondance map
correspondancemapu=zeros(sy*samplingfactor,sx*samplingfactor);
correspondancemapv=zeros(sy*samplingfactor,sx*samplingfactor);
for yy=2*samplingfactor:sy*samplingfactor-3*samplingfactor
    for xx=2*samplingfactor:sx*samplingfactor-3*samplingfactor
        %if xx==1099
        %   display 'ici'
        %end
        H =reshape( InterpolationFunction(  xx/samplingfactor,yy/samplingfactor,HomographyGrid),3,3);
        p2=H*[xx,yy,1]'; %transformation homographique inverse
        %ud=round(p2(1)/p2(3));
        %vd=round(p2(2)/p2(3));
        ud=p2(1)/p2(3);
        vd=p2(2)/p2(3);
        correspondancemapu(yy,xx)=ud;
        correspondancemapv(yy,xx)=vd;
    end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%save to a correspondance map using an openCV compatible format 
%file saved with .map extension
map=[correspondancemapv;correspondancemapu];
imagedirectory='./';
mapname=sprintf('%s/correspondance.map',imagedirectory);
saveRawFloat(map, mapname);
display('correspondance.map file saved in imagedirectory');
%future use: process the images using python bindings of opencv remap
%function: see /media/HD500GO/saveHDDgarossos/menage_ocamcalib/remap
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% Apply the interpolated homography to a synthetic image.
%%% it visualizes the equivalent of the control grid but in the source
%%% image plane
imoutsinu=zeros(sy*samplingfactor,sx*samplingfactor);
imoutsinv=zeros(sy*samplingfactor,sx*samplingfactor);
imoutsinuv=zeros(sy*samplingfactor,sx*samplingfactor);
imoutsinvu=zeros(sy*samplingfactor,sx*samplingfactor);
imoutcircle=zeros(sy*samplingfactor,sx*samplingfactor);
imoutradial=zeros(sy*samplingfactor,sx*samplingfactor);
imoutgrid=zeros(sy*samplingfactor,sx*samplingfactor);
for yy=2*samplingfactor:size(imoutsinu,1)-3*samplingfactor
    for xx=2*samplingfactor:size(imoutsinu,2)-3*samplingfactor
        ud=correspondancemapu(yy,xx);
        vd=correspondancemapv(yy,xx);
        %for a square grid
        valpix=127*mod(floor(ud/samplingfactor),2) + 127*mod(floor(vd/samplingfactor),2) ;
        imoutgrid(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        %for a sinus wave in u direction
        valpix=uint8(127+127*sin(ud/2.5));
        imoutsinu(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        %for a sinus wave in v direction
        valpix=uint8(127+127*sin(vd/2.5));
        imoutsinv(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        %for a sinus wave in uv diagonal direction
        valpix=uint8(127+127*sin((vd+ud)/(2*2.5)));
        imoutsinuv(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        %for a sinus wave in vu diagonal direction
        valpix=uint8(127+127*sin((vd-ud)/(2*2.5)));
        imoutsinvu(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        %for a sinus wave in circle direction
        valpix=uint8(127+127*sin((norm([(ud-750);(vd-500)],2) /2.5)));
        imoutcircle(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        %for a sinus wave in radial direction
        angle=atan2((vd-500),(ud-750))*20;
        valpix=uint8(127+127*sin(angle));
        imoutradial(yy,xx)=valpix; %on attribue la couleur du pixel concerné
    end
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%display images
figure
subplot(3,1,1); image(imoutgrid); axis equal;colormap(gray(256));
subplot(3,1,2); image(imoutsinu); axis equal;colormap(gray(256));
subplot(3,1,3); image(imoutsinv); axis equal;colormap(gray(256));
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%save images
imwrite(uint8(imoutgrid),'imoutgrid.png');
imwrite(uint8(imoutsinu),'imoutu.png');
imwrite(uint8(imoutsinv),'imoutv.png');
imwrite(uint8(imoutsinuv),'imoutuv.png');
imwrite(uint8(imoutsinvu),'imoutvu.png');
imwrite(uint8(imoutcircle),'imoutcircle.png');
imwrite(uint8(imoutradial),'imoutradial.png');
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%generate sequences of images
nn=0;
for angle=0:2*pi/60:2*pi
    if angle~=0
        nn=nn+1
    end
    for yy=2*samplingfactor:size(imoutsinu,1)-3*samplingfactor
        for xx=2*samplingfactor:size(imoutsinu,2)-3*samplingfactor
            ud=correspondancemapu(yy,xx);
            vd=correspondancemapv(yy,xx);
            %for a sinus wave in u direction
            valpix=uint8(127+127*sin(angle+(ud/2.5)));
            imoutsinu(yy,xx)=valpix; %on attribue la couleur du pixel concerné
            %for a sinus wave in v direction
            valpix=uint8(127+127*sin(angle+(vd/2.5)));
            imoutsinv(yy,xx)=valpix; %on attribue la couleur du pixel concerné
        end
    end
    imgname=sprintf('%s/sinu%02i.png',imagedirectory,nn);
    imwrite(uint8(imoutsinu),imgname);
    imgname=sprintf('%s/sinv%02i.png',imagedirectory,nn);
    imwrite(uint8(imoutsinv),imgname);
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%compute the mpg videos... does not work from within matlab, invoke it
%through a linux shell
%system('avconv -f image2 -i sinu%02d.png -f avi -vcodec mpeg4 -b 4000k -g 300 -bf 2 -y ./videosinu.mpg')
%system('avconv -f image2 -i sinv%02d.png -f avi -vcodec mpeg4 -b 4000k -g 300 -bf 2 -y ./videosinv.mpg');

Results

Garbage

$\left(\begin{array}{ccc} {\mathrm{q1}}^2 + {\mathrm{q2}}^2 - {\mathrm{q3}}^2 - {\mathrm{q4}}^2 & 2\, \mathrm{q2}\, \mathrm{q3} - 2\, \mathrm{q1}\, \mathrm{q4} & 2\, \mathrm{q1}\, \mathrm{q3} + 2\, \mathrm{q2}\, \mathrm{q4}\\ 2\, \mathrm{q1}\, \mathrm{q4} + 2\, \mathrm{q2}\, \mathrm{q3} & {\mathrm{q1}}^2 - {\mathrm{q2}}^2 + {\mathrm{q3}}^2 - {\mathrm{q4}}^2 & 2\, \mathrm{q3}\, \mathrm{q4} - 2\, \mathrm{q1}\, \mathrm{q2}\\ 2\, \mathrm{q2}\, \mathrm{q4} - 2\, \mathrm{q1}\, \mathrm{q3} & 2\, \mathrm{q1}\, \mathrm{q2} + 2\, \mathrm{q3}\, \mathrm{q4} & {\mathrm{q1}}^2 - {\mathrm{q2}}^2 - {\mathrm{q3}}^2 + {\mathrm{q4}}^2 \end{array}\right)
$

$\left(\begin{array}{ccccccccccc} 2\, \mathrm{q1} & 2\, \mathrm{q2} & - 2\, \mathrm{q3} & - 2\, \mathrm{q4} & -\frac{\mathrm{nx}}{d} & 0 & 0 & -\frac{\mathrm{tx}}{d} & 0 & 0 & \frac{\mathrm{nx}\, \mathrm{tx}}{d^2}\\ - 2\, \mathrm{q4} & 2\, \mathrm{q3} & 2\, \mathrm{q2} & - 2\, \mathrm{q1} & -\frac{\mathrm{ny}}{d} & 0 & 0 & 0 & -\frac{\mathrm{tx}}{d} & 0 & \frac{\mathrm{ny}\, \mathrm{tx}}{d^2}\\ 2\, \mathrm{q3} & 2\, \mathrm{q4} & 2\, \mathrm{q1} & 2\, \mathrm{q2} & -\frac{\mathrm{nz}}{d} & 0 & 0 & 0 & 0 & -\frac{\mathrm{tx}}{d} & \frac{\mathrm{nz}\, \mathrm{tx}}{d^2}\\ 2\, \mathrm{q4} & 2\, \mathrm{q3} & 2\, \mathrm{q2} & 2\, \mathrm{q1} & 0 & -\frac{\mathrm{nx}}{d} & 0 & -\frac{\mathrm{ty}}{d} & 0 & 0 & \frac{\mathrm{nx}\, \mathrm{ty}}{d^2}\\ 2\, \mathrm{q1} & - 2\, \mathrm{q2} & 2\, \mathrm{q3} & - 2\, \mathrm{q4} & 0 & -\frac{\mathrm{ny}}{d} & 0 & 0 & -\frac{\mathrm{ty}}{d} & 0 & \frac{\mathrm{ny}\, \mathrm{ty}}{d^2}\\ - 2\, \mathrm{q2} & - 2\, \mathrm{q1} & 2\, \mathrm{q4} & 2\, \mathrm{q3} & 0 & -\frac{\mathrm{nz}}{d} & 0 & 0 & 0 & -\frac{\mathrm{ty}}{d} & \frac{\mathrm{nz}\, \mathrm{ty}}{d^2}\\ - 2\, \mathrm{q3} & 2\, \mathrm{q4} & - 2\, \mathrm{q1} & 2\, \mathrm{q2} & 0 & 0 & -\frac{\mathrm{nx}}{d} & -\frac{\mathrm{tz}}{d} & 0 & 0 & \frac{\mathrm{nx}\, \mathrm{tz}}{d^2}\\ 2\, \mathrm{q2} & 2\, \mathrm{q1} & 2\, \mathrm{q4} & 2\, \mathrm{q3} & 0 & 0 & -\frac{\mathrm{ny}}{d} & 0 & -\frac{\mathrm{tz}}{d} & 0 & \frac{\mathrm{ny}\, \mathrm{tz}}{d^2}\\ 2\, \mathrm{q1} & - 2\, \mathrm{q2} & - 2\, \mathrm{q3} & 2\, \mathrm{q4} & 0 & 0 & -\frac{\mathrm{nz}}{d} & 0 & 0 & -\frac{\mathrm{tz}}{d} & \frac{\mathrm{nz}\, \mathrm{tz}}{d^2} \end{array}\right)$

$\left(\begin{array}{cccccccc} \frac{u_{1}1}{\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1} & \frac{\mathrm{v11}}{\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1} & \frac{1}{\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1} & 0 & 0 & 0 & -\frac{u_{1}1\, \left(\mathrm{h13} + \mathrm{h11}\, u_{1}1 + \mathrm{h12}\, \mathrm{v11}\right)}{{\left(\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1\right)}^2} & -\frac{\mathrm{v11}\, \left(\mathrm{h13} + \mathrm{h11}\, u_{1}1 + \mathrm{h12}\, \mathrm{v11}\right)}{{\left(\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1\right)}^2}\\ 0 & 0 & 0 & \frac{u_{1}1}{\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1} & \frac{\mathrm{v11}}{\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1} & \frac{1}{\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1} & -\frac{u_{1}1\, \left(\mathrm{h23} + \mathrm{h21}\, u_{1}1 + \mathrm{h22}\, \mathrm{v11}\right)}{{\left(\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1\right)}^2} & -\frac{\mathrm{v11}\, \left(\mathrm{h23} + \mathrm{h21}\, u_{1}1 + \mathrm{h22}\, \mathrm{v11}\right)}{{\left(\mathrm{h31}\, u_{1}1 + \mathrm{h32}\, \mathrm{v11} + 1\right)}^2}\\ \frac{\mathrm{u12}}{\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1} & \frac{\mathrm{v12}}{\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1} & 0 & 0 & 0 & -\frac{\mathrm{u12}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u12} + \mathrm{h12}\, \mathrm{v12}\right)}{{\left(\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1\right)}^2} & -\frac{\mathrm{v12}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u12} + \mathrm{h12}\, \mathrm{v12}\right)}{{\left(\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1\right)}^2}\\ 0 & 0 & 0 & \frac{\mathrm{u12}}{\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1} & \frac{\mathrm{v12}}{\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1} & -\frac{\mathrm{u12}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u12} + \mathrm{h22}\, \mathrm{v12}\right)}{{\left(\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1\right)}^2} & -\frac{\mathrm{v12}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u12} + \mathrm{h22}\, \mathrm{v12}\right)}{{\left(\mathrm{h31}\, \mathrm{u12} + \mathrm{h32}\, \mathrm{v12} + 1\right)}^2}\\ \frac{\mathrm{u13}}{\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1} & \frac{\mathrm{v13}}{\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1} & 0 & 0 & 0 & -\frac{\mathrm{u13}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u13} + \mathrm{h12}\, \mathrm{v13}\right)}{{\left(\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1\right)}^2} & -\frac{\mathrm{v13}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u13} + \mathrm{h12}\, \mathrm{v13}\right)}{{\left(\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1\right)}^2}\\ 0 & 0 & 0 & \frac{\mathrm{u13}}{\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1} & \frac{\mathrm{v13}}{\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1} & -\frac{\mathrm{u13}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u13} + \mathrm{h22}\, \mathrm{v13}\right)}{{\left(\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1\right)}^2} & -\frac{\mathrm{v13}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u13} + \mathrm{h22}\, \mathrm{v13}\right)}{{\left(\mathrm{h31}\, \mathrm{u13} + \mathrm{h32}\, \mathrm{v13} + 1\right)}^2}\\ \frac{\mathrm{u14}}{\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1} & \frac{\mathrm{v14}}{\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1} & 0 & 0 & 0 & -\frac{\mathrm{u14}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u14} + \mathrm{h12}\, \mathrm{v14}\right)}{{\left(\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1\right)}^2} & -\frac{\mathrm{v14}\, \left(\mathrm{h13} + \mathrm{h11}\, \mathrm{u14} + \mathrm{h12}\, \mathrm{v14}\right)}{{\left(\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1\right)}^2}\\ 0 & 0 & 0 & \frac{\mathrm{u14}}{\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1} & \frac{\mathrm{v14}}{\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1} & \frac{1}{\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1} & -\frac{\mathrm{u14}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u14} + \mathrm{h22}\, \mathrm{v14}\right)}{{\left(\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1\right)}^2} & -\frac{\mathrm{v14}\, \left(\mathrm{h23} + \mathrm{h21}\, \mathrm{u14} + \mathrm{h22}\, \mathrm{v14}\right)}{{\left(\mathrm{h31}\, \mathrm{u14} + \mathrm{h32}\, \mathrm{v14} + 1\right)}^2} \end{array}\right)$

$\left(\begin{array}{c} \frac{\mathrm{fx}\, x + \mathrm{pu}\, z}{z} - \frac{\mathrm{fx}\, x - \mathrm{bp} + \mathrm{pu}\, z}{z}\\ 0 \end{array}\right)$

BSPLINES

$\left(\begin{array}{ccccccccc}  - \frac{u^3}{6} + \frac{u^2}{2} - \frac{u}{2} + \frac{1}{6} & 0 & \frac{u^3}{2} - u^2 + \frac{2}{3} & 0 &  - \frac{u^3}{2} + \frac{u^2}{2} + \frac{u}{2} + \frac{1}{6} & 0 & \frac{u^3}{6} & 0 &  - \left(\mathrm{p1x} - \mathrm{p2x}\right)\, \left( - u^2 + u + \frac{1}{2}\right) - \left(\mathrm{p0x} - \mathrm{p1x}\right)\, \left(\frac{u^2}{2} - u + \frac{1}{2}\right) - \frac{u^2\, \left(\mathrm{p2x} - \mathrm{p3x}\right)}{2}\\ 0 &  - \frac{u^3}{6} + \frac{u^2}{2} - \frac{u}{2} + \frac{1}{6} & 0 & \frac{u^3}{2} - u^2 + \frac{2}{3} & 0 &  - \frac{u^3}{2} + \frac{u^2}{2} + \frac{u}{2} + \frac{1}{6} & 0 & \frac{u^3}{6} &  - \left(\mathrm{p1y} - \mathrm{p2y}\right)\, \left( - u^2 + u + \frac{1}{2}\right) - \left(\mathrm{p0y} - \mathrm{p1y}\right)\, \left(\frac{u^2}{2} - u + \frac{1}{2}\right) - \frac{u^2\, \left(\mathrm{p2y} - \mathrm{p3y}\right)}{2} \end{array}\right)$

homography.txt · Dernière modification: 2017/10/31 15:57 par bvandepo