MATLAB: How to find minimum Pixel value

Question

Hi there,

I have 64*64 pixel Image and value are measured in 40s withe Image Rate (47 1/s). Image file is 64*64*1913 double, I want to find location for minimum Pixel Value (row and colmns) in region (32:64, 32:64) in all of the time. I used these two codes but it didn't work.

[row, column] = find(min(squeeze(nanmean(squeeze(nanmean((imgfilt(32:64,32:64,:)))))) == 1))
  row =
     []
column =
     []
% % % % % % % % % % % % % % % % % % %      
     
>> M = (min(nanmean(nanmean( imgfilt(32:64,32:64,: ),2),1)));
[min_val,idx] = min(M(:))
[row,col] = ind2sub(M,idx)
min_val =
  -3.6858e+14
idx =
     1
row =
     1
col =
     1

Answer 1

You should be able to do

	minValue = min(thisImage(:))
	[row, column] = find(thisImage == minValue);

for each time point (slice of your 3-D image volume). Here is a full demo:

imgfilt = randi(65535, 64, 64, 1913); % Create sample data.  You, of course, would use your own.
imgfilt(44:66) = nan;
[rows, columns, numberOfTimePoints] = size(imgfilt)
for slice = 1 : numberOfTimePoints
	% Get the image for this time point.
	thisImage = imgfilt(32:end, 32:end, slice);
	minValue = min(thisImage(:));
	[row, column] = find(thisImage == minValue);
	% To get original indices, need to add 31 to the row and column
	row = row + 31;
	column = column + 31;
	% Store the rows and columns where this time point image equals the min.
	% We are using a cell array because each image may have a different number 
	% of locations where the min occurs.
	ca{slice, 1} = row;
	ca{slice, 2} = column;
	% For fun, print them out.
	for k = 1 : length(row)
		r = row(k);
		c = column(k);
		fprintf('For time point %d, the min value of %f occurs at row %d, column %d.\n', ...
			slice, imgfilt(r, c, slice), r, c);
	end
end