find pixels value in a volume using indexing/pixel position

hello

I have a 500X3 matrix named PixelPos where it represents pixel position in a volume x, where the first column PixelPos(:,1) has the row numbers, PixelPos(:,2) is the column number and PixelPos(:,3) is the slice number. i want to get the value for these pixels, i used a for loop to find the value for each pixel in x but it is very time consuming, is there a function in matlab that could be helpful ?

thanks Hannah

Answer 1

[Image Analyst]

Looping 500 times should not be time consuming. Just make sure you access the right most values (the Z values) less frequently so you don't have a lot of memory thrashing.

clc;
PixelPos = randi(9, [50,3]); % Sample data
% Get sort order based on column 3.
[~, sortOrder] = sort(PixelPos(:,3)); 
sortedPositions = PixelPos(sortOrder, :);
for k = 1 : length(sortedPositions)
  row = sortedPositions(k, 1);
  col = sortedPositions(k, 2);
  slice = sortedPositions(k, 3);
  value = array3d(row, columns, slice);
  fprintf('For row=%d, column=%2, slice=%d, the value = %d',...
    row, col, slice, value);
end

[Hannah]

Thank you. am working with medical data and anticipating that for the data i will receive the matrix size could increase to a large number ~ 10^7. so i was wondering if there is another way other than using a loop. i found sub2ind function in matlab to work well.

rows = PixelPos(:,1);

colm = PixelPos(:,2);

slice = PixelPos(:,3);

linearInd = sub2ind(size(x), rows, colm,slice);

value = x(linearInd)

Hannah x

[Image Analyst]

Try it and see.