Save one image as part of a larger image

2012 5 10
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Hi all,
I have processed image data into a 10x512 pixel array. I have multiple images all this size and I would like to display them all side by side on a single larger image. I have created a blank image using zeros of size 1000x512 (i.e. I have 100 images in total, therefore 10 pixels x 100 images) but am having trouble getting my smaller image to display. How could I approach this?
Kind regard and thanks, Susan

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Geoff
Geoff 2012-5-10

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Let's just assume that all your images are in a 3D matrix and you want to slap them onto a canvas:
canvas = zeros(1000, 512); % Target image
images = rand(10, 512, 100); % 100 very useless images =)
Now, in this case, there are clever MatLab functions, but I'll stick to a simple loop so you see what's going on (and that's adaptable if your images are stored in some other way).
for n = 1:100
rows = (n-1) * 10 + (1:10);
canvas(rows, :) = images(:,:,n);
end
So, for each image (indexed by n), you calculate a range of row indices for your 10 rows. The value (n-1) * 10 gives the zero-based position of the first row of the 'n'th image, and then you add that to the vector 1:10. ie image 1 is rows 1:10, image 2 is rows 11:20, etc...
The slice canvas(rows, :) is then a 10-by-512 address, into which you assign the values from your 'n'th image (also 10-by-512).

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Susan
Susan 2012-5-15
Hi Geoff,
Thanks for your reply - I adopted your method and it works!! :)
However, I've still a problem. I'm processing 500 images in total - 10 (i_B in code) groups of 50 (num_A in code) - producing an image for each iteration of i_B (yielding 10 images in total of pixel size (N,50)). The code works fine if I set i_B = 1, 2, 3, etc. manually but I would like to automate it (so that the code will output and save 10 images in this case) as I will have a larger number of images in the future. The error I am getting is:
??? Subscripted assignment dimension mismatch
at the portion of the code below indicated by ******.
I would greatly appreciate any advice!
Kind regards,
Susan
P.s. I've omitted some of the preceding code for clarity (will not affect operation)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
num_B = 10
num_A = 50;
for i_B = 1:num_B
for i = 1:num_A
file = sprintf('%s%s%d%s',folder,filename,((100*(i_B-1))+1+(2*(i-1))),suffix);
A = imread(file);
mA = mean(A);
mA(1) = mA(2);
fit = polyfit(nm,mDC,4);
pDC = polyval(fit,nm);
S = mA./pDC;
S = S - mean(S);
Ses = interp1(nu,S,kes);
abs_s_tau = abs(fft(Ses));
img(:,i) = abs_s_tau'; ******
end
img = img(1:(pixel/2),:);
img = log10(img);
img = mat2gray(img);
img = img(1:pixel/2,:);
figure(i_B); clf
imshow(img);
file_saved = strcat(folder,'B-scan_',num2str(i_Bscan),'.png');
imwrite(img, file_saved ,'png', 'BitDepth', 16);
end

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Susan
Susan 2012-5-15

0 个投票

Just cracked it myself. Simple mistake. Needed to initialise the image inside the first for loop. :)
num_B = 10
num_A = 50;
for i_B = 1:num_B
img = zeros(pixel,num_A);
img(i_B);
for i = 1:num_Ascans
.
.
.
.
end
end

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