Forming a giant array of multiple 64 x 64 matrices - arrays

Question

I am working video shot boundary detection using matlab. Here is my code snippet
clc;
clear all;
[file path] = uigetfile('*.avi','Pick a Video');% this line opens a pop up window so that you can choose your video for further processing
video = VideoReader([path file]);% the video chosen through UI get stored in video object
numOfFrames = video.NumberOfFrames;% this will be a number (total number of frames in your chosen video)
%allFrames = read(video);% catching all the frames from the video in object allFrames
for i=1:1:numOfFrames
try
lFrame = read(video, i);%frames(:, :, :, i);
catch
break;
end
lRFrame = lFrame(:,:,1);
lGFrame = lFrame(:,:,2);
lBFrame = lFrame(:,:,3);
lGray = 0.299*lRFrame + 0.587*lGFrame + 0.114*lBFrame;
grayImage = imresize(lGray, [256 256]);
% step 2 of the algorithm begins from here %
meanFilterFunction = #(theBlockStructure) mean2(theBlockStructure.data(:)) * ones(1,1, class(theBlockStructure.data));
blockSize = [4 4];
blockyImage4 = blockproc(single(grayImage), blockSize, meanFilterFunction);
end
I am getting a 64 x 64 image in blockyImage4 but since it is in a loop , the value flushes itself in very next iteration every time.
I want an array of images which can store (possibly all) images(matrices). and i should have access to them all. if all the images could not be stored in an array then how to store only two images of consecutive iterations since i need 'i' and "i+1" th image to find out the diffrence between them. Please help

Answer 1

You want to store 3D (x,y,time) data in Matlab? Do it either in a cell array or a 3D array. For the array don't forget to preallocate the needed size to avoid performance drops.
So either:
blockyimages = cell(numOfFrames, 1);
for i=1:1:numOfFrames
...
blockyimages{i} = blockproc(single(grayImage), blockSize, meanFilterFunction);
end
% access the blocky image of the ith frame with blockyimages{i}
% you could even do blockyimages = cat(3, blockyimages{:}) to convert to a 3d matrix
or
blockyimages = zeros(64, 64, numOfFrames); % better frame sizes / block sizes
for i=1:1:numOfFrames
...
blockyimages(:, :, i) = blockproc(single(grayImage), blockSize, meanFilterFunction);
end
% access the blocky image of the ith frame with blockyimages(:, :, i)
So, if you chose the second option and later want to do something with the blockyimages again, just make a second pass through the loop. For example if you want to compute the differences of consecutive blockyimages.
diffblockyimages = zeros(64, 64, numOfFrames - 1);
for i = 1 : numOfFrames - 1
framei = blockyimages(:, :, i);
frameiplusone = blockyimages(:, :, i+1);
diffblockyimages(:, :, i) = frameiplusone - framei;
end
Although the same could have been achieved in the special case of the difference also as
diffblockyimages = diff(blockyimages, 1, 3);

Answer 2

Since my comment is blocked I present possible solution:
tested and works fine for me
file_path = uigetfile('*.avi','Pick a Video');% this line opens a pop up window so that you can choose your video for further processing
video = VideoReader(file_path);% the video chosen through UI get stored in video object
numOfFrames = video.NumberOfFrames;% this will be a number (total number of frames in your chosen video)
%allFrames = read(video);% catching all the frames from the video in object allFrames
all_frames = cell(1,numOfFrames);
for i=1:numOfFrames %default step is always 1
try
lFrame = read(video, i);%frames(:, :, :, i);
catch
break;
end
lGray = rgb2gray(lFrame);
grayImage = imresize(lGray, [256 256]);
all_frames{1,i} = grayImage;
end
now you have all frames in all_frames array
access is easy:
img1 = all_frames{1,1}; imshow(img1);
img2 = all_frames{1,2}; imshow(img2);