Finding areas of data based on value threshold and contiguous size, both height and length.

Hi,

I would like to find the indices of this matrix where values are >3 and are larger than 3 x 5 in size. I have tried using the Image Processing Toolbox and binaryVector...

Any help much appreciated.

A = [2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5;

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5;

2.5 2.5 3.5 3.5 3.5 3.5 3.5 3.5 2.5 2.5 2.5 2.5;

2.5 2.5 3.5 3.5 3.5 3.5 3.5 3.5 2.5 2.5 2.5 2.5;

2.5 2.5 3.5 3.5 3.5 3.5 3.5 3.5 2.5 2.5 2.5 2.5;

2.5 2.5 3.5 3.5 3.5 3.5 3.5 3.5 2.5 2.5 2.5 2.5;

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5;

2.5 3.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5;

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 3.5 3.5 2.5;

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 3.5 3.5 2.5;

2.5 2.5 3.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5;

2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5]

Answer 1

[Jan]

Start with:

B = (A > 3);

   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0
   0   0   1   1   1   1   1   1   0   0   0   0
   0   0   1   1   1   1   1   1   0   0   0   0
   0   0   1   1   1   1   1   1   0   0   0   0
   0   0   1   1   1   1   1   1   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0
   0   1   0   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   1   1   0
   0   0   0   0   0   0   0   0   0   1   1   0
   0   0   1   0   0   0   0   0   0   0   0   0
   0   0   0   0   0   0   0   0   0   0   0   0   

Now mention, what you have tried with the image processing tooolbox and which problems occurred.

[Nick Ward]

Hi Jan,

Thank you. So, I have the binary image you replied with.

I now want to find the indices of the largest area of 1s...

I used bwlabel to label each region >3, and then regionprops of area and perimeter to exclude anything below the 3 x 5 array threshold I require. I can only retrieve every value >3.

Ideally, I would like to dump each region of data >3 and greater than 3 x 5 size into new matrices and output their indices. The data set is I am working on is logged temperature from a oceanographic mooring - I am looking for large water masses >3 C, for context.

I have tried using this code from Image Analyst;

% Find logical vector of AW regions (>3 degrees)

binaryVector = A > 3

% Label each region with a label - an "ID" number.

[labeledVector, numRegions] = bwlabel(binaryVector)

% Measure lengths of each region and the indexes

measurements = regionprops(labeledVector, A, 'Area', 'PixelValues');

% Find regions where the area (length) are 20 or greater and

% put the values into a cell of a cell array

for k = 1 : numRegions

if measurements(k).Area >= 20

% Area (length) is 3 or greater, so store the values.

ca{k} = measurements(k).PixelValues;

end

end

% Display the regions that meet the criteria:

celldisp(ca)