Question

我需要使用图像2中的rgb值更新图像1以获取特定坐标。

我有两个2d矩阵（im1Cart_toupdate 2x114056和im2EstCart_tocopy来自2x114056）。这些包含有序的x-y对，我想将rgb值从图像2复制到图像1。

即。有114,056像素，我想复制颜色。

im1（440x1370x3）和im2（240x320x3）是图像阵列。注意im2将被拉伸，因此来自im2的一些像素将在im2EstCart_tocopyfrom中出现多次。

我需要一种有效的方法来实现这一点，因为即使使用上述图像大小，我当前的实现也非常慢。我原以为可能有一些方法使用sub2ind - 但我不知道如何用3d数组做这个。

这是我目前的代码。这是for循环，它杀了我！

%Create a matrix of all pixel coordinates in im1 (homogenised form)
[im1gridx im1gridy]=meshgrid(1:im1width,1:im1height);
im1Cart = [im1gridx(:) im1gridy(:)]';
im1Hom = [im1Cart; ones(1,numel(im1gridy))];

%transform pixel positions with homography (HEst is a matrix built
%elsewhere) to find where they are in the coordinates of image 2
im2EstHom = HEst*im1Hom;
im2EstCart = im2EstHom(1:2,:)./repmat(im2EstHom(3,:),2,1);
im2EstCart = round(im2EstCart);

%check if the the transformed position is within the boundary of image 2 
validCoords = im2EstCart(1,:)>0 & im2EstCart(2,:)>0 & im2EstCart(1,:)<=im2width & im2EstCart(2,:)<=im2height;
im1Cart_toupdate=im1Cart(:,validCoords);
im2EstCart_tocopyfrom=im2EstCart(:,validCoords);

%copy colour from image 2 to image 1 - currently pixel by pixel
%but CAN THIS BE VECTORISED?
for i=1:size(im1Cart_toupdate,2)
    im1y=im1Cart_toupdate(1,i);
    im1x=im1Cart_toupdate(2,i);
    im2y=im2EstCart_tocopyfrom(1,i);
    im2x=im2EstCart_tocopyfrom(2,i);
    im1(im1y,im1x,:) = im2(im2y,im2x,:);
    drawnow
end

非常感谢任何建议！

Answer 1

方法＃1

这是使用linear indexing和bsxfun -

的一种矢量化方法

[m2,n2,r2] = size(im2);
RHS_idx1 = (im2EstCart_tocopyfrom(2,:)-1)*m2 + im2EstCart_tocopyfrom(1,:)
RHS_allidx = bsxfun(@plus,RHS_idx1(:),(0:r2-1)*m2*n2)

[m1,n1,r1] = size(im1);
LHS_idx1 = (im1Cart_toupdate(2,:)-1)*m1 + im1Cart_toupdate(1,:)
LHS_allidx = bsxfun(@plus,LHS_idx1(:),(0:r1-1)*m1*n1)

im1(LHS_allidx) = im2(RHS_allidx)

方法＃2

这是另一种方法，在合并前两个维度后，将输入3D数组重新整形为2D数组，然后使用linear indexing提取和设置值，最后重新变换回原始数据3D大小，如此 -

[m2,n2,r2] = size(im2)
RHS_idx1 = (im2EstCart_tocopyfrom(2,:)-1)*m2 + im2EstCart_tocopyfrom(1,:)
im2r = reshape(im2,[],r2) 

[m1,n1,r1] = size(im1)
LHS_idx1 = (im1Cart_toupdate(2,:)-1)*m1 + im1Cart_toupdate(1,:)
im1r = reshape(im1,[],r1)
im1r(LHS_idx1,:) = im2r(RHS_idx1,:)

im1 = reshape(im1r,size(im1));

MATLAB - 将特定值从一个3d数组复制到另一个3d数组

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