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Reshape Video Matrix Into Long RGB Matrix and Back

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Royi Avital
Royi Avital on 29 Jun 2015
Answered: Royi Avital on 30 Jun 2015
Hello,
Let's say I have a Video Matrix `mVideoMatrix`.
This is a 4D matrix (Numnber of Rows x Number of Columns x Number of Color Channels x Number of Frames).
For instance, 360 x 480 x 3 x 10, namely 360 Rows, 480 Columns, 3 RGB Channels and 10 Frames.
Now I want to make it a long RGB image where each frame is beneath the previous one. Is the a vectorized way to do so?
How would you formulate the way back, namely from the image into the Video?
I'm attaching sample codes which use "For Loop".
At first, reshaping RGB Video into long RGB Image:
function [ mOutputImage ] = ReshapeVideoIntoImage( tInputVideo )
numRows = size(tInputVideo, 1);
numCols = size(tInputVideo, 2);
numChannels = size(tInputVideo, 3);
numFrames = size(tInputVideo, 4);
mOutputImage = zeros([(numFrames * numRows), numCols, numChannels]);
firstRowIdx = 1;
for iFrameIdx = 1:numFrames
vRows = (firstRowIdx - 1) + [1:numRows];
mOutputImage(vRows, :, :) = tInputVideo(:, :, :, iFrameIdx);
firstRowIdx = firstRowIdx + numRows;
end
end
Going back, from long RGB Image into RGB Video:
function [ tOutputVideo ] = ReshapeImageIntoVideo( mInputtImage, videoNumRows )
numRows = size(mInputtImage, 1);
numCols = size(mInputtImage, 2);
numChannels = size(mInputtImage, 3);
videoNumFrames = numRows / videoNumRows;
tOutputVideo = zeros([videoNumRows, numCols, numChannels, videoNumFrames]);
firstRowIdx = 1;
for iFrameIdx = 1:videoNumFrames
vRows = (firstRowIdx - 1) + [1:videoNumRows];
tOutputVideo(:, :, :, iFrameIdx) = mInputtImage(vRows, :, :);
firstRowIdx = firstRowIdx + videoNumRows;
end
end
Thank You.

Accepted Answer

Royi Avital
Royi Avital on 30 Jun 2015
I think I have a solution (At least one).
going from video into one lone image:
function [ mOutputImage ] = ReshapeVideoIntoImage( tInputVideo )
numRows = size(tInputVideo, 1);
numCols = size(tInputVideo, 2);
numChannels = size(tInputVideo, 3);
numFrames = size(tInputVideo, 4);
mOutputImage = permute(tInputVideo, [1, 4, 2, 3]);
mOutputImage = reshape(mOutputImage, [(numRows * numFrames), numCols, numChannels]);
end
Going from Long Image into Video:
function [ tOutputVideo ] = ReshapeImageIntoVideo( mInputtImage, videoNumRows )
numRows = size(mInputtImage, 1);
numCols = size(mInputtImage, 2);
numChannels = size(mInputtImage, 3);
videoNumFrames = numRows / videoNumRows;
tOutputVideo = reshape(mInputtImage, [videoNumRows, videoNumFrames, numCols, numChannels]);
tOutputVideo = permute(tOutputVideo, [1, 3, 4, 2]);
end
Thank You.
P.S.
If there is an even faster way, I'd be happy to see.

More Answers (2)

Sid
Sid on 29 Jun 2015
Can you use something like this?
% Concatenate along 'fourth' dimension.
alpha = cat(4,newArray(:,:,:));
% Extract every third color plane, starting with 1.
red = alpha(:,:,1:3:size(alpha,3));
red = vertcat(red(:,:));
% Extract every third color plane, starting with 2.
green = alpha(:,:,2:3:size(alpha,3));
green = vertcat(green(:,:));
% Extract every third color plane, starting with 3.
blue = alpha(:,:,3:3:size(alpha,3));
blue = vertcat(blue(:,:));
RGB = cat(3,red,green,blue);
figure, imshow(RGB)
where newArray refers to the original 4-D array.
Perhaps I'm missing something, but I'm not sure I completely follow the logic of concatenating images?
Also, for more info, the article here about multidimensional arrays might prove useful. Good luck!
HTH.
  1 Comment
Royi Avital
Royi Avital on 29 Jun 2015
Hi Sid,
I already have the video in 4-D Array.
As I specified above, the 4-D array is as following: (Num Rows x Num Columns x 3 (RGB) x Num Frames).
I want to create a 3-D matrix which its dimensions are ((NumRowx * Num Num Frame) x Num Columns x Num Channel (3, RGB)).
Namely to put frame below frame and then going back.
I added a sample code.
Thank You.

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Image Analyst
Image Analyst on 29 Jun 2015
To stitch the frames together vertically, do this:
numFrames = size(myVideo, 4);
stitchedImage = [];
for k = 1 : numFrames
stitchedImage = [stitchedImage; myVideo(:,:,:,k)];
end
  1 Comment
Royi Avital
Royi Avital on 30 Jun 2015
Hi, You can see my code above does the same.
I thought there would be a faster way, a vectorized way (I think it can be done using permute).

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