How can I remove unwanted area by mask?

Dear All,

Could anyone help to remove unwanted area by using a mask? as figure bellow

• I create a mask by thresholding
• Then want to remove unwanted area by the mask

% here is my code
I = imread('coins.png');
X = imadjust(I);

% Threshold image - manual threshold
BW = im2gray(X) > 5.355000e+01;

% Dilate mask with default
radius = 1;
decomposition = 4;
se = strel('disk', radius, decomposition);
BW = imdilate(BW, se);

% Create masked image.
maskedImage = X;
maskedImage(~BW) = 0;
imwrite(maskedImage,'mask.png')

[DGM]

What's wrong with the code as given?

% here is my code
I = imread('coins.png');
X = imadjust(I);

% Threshold image - manual threshold
BW = im2gray(X) > 5.355000e+01;

% Dilate mask with default
radius = 1;
decomposition = 4;
se = strel('disk', radius, decomposition);
BW = imdilate(BW, se);

% Create masked image.
maskedImage = X;
maskedImage(~BW) = 0;
%imwrite(maskedImage,'mask.png')
imshow(maskedImage)

[Jenifer NG]

thanks you my simple mistake :((

[Jenifer NG]

How can I put process for multiple image ?

Answer 1

[DGM]

Just get the file names somehow and read/process/write the files in a loop.

This is one example based on simple pattern matching.

% you'll have to set these directories
inFolder = 'sources'; % this is just where i had some test files
outFolder = './'; % the folder to place the outputs in
outfiletype = '.png'; % this makes it easy to change
filePattern = fullfile(inFolder, '*.jpg'); % select which files to load

allFiles   = dir(filePattern);
for k = 1:length(allFiles)
    baseFileName = allFiles(k).name;
    fullFileName = fullfile(inFolder, baseFileName);
    
    % process image...
    I = imread(fullFileName);
    I = im2gray(I); % image needs to be gray if using imadjust() like that
    I = imadjust(I);
    
    % Threshold image - manual threshold
    % you'll have to come up with a way to do the thresholding 
    % that's effective for all images.  that's not something i can guess
    BW = I > 5.355000e+01;
    
    % Dilate mask with default
    radius = 1;
    decomposition = 4;
    se = strel('disk', radius, decomposition);
    BW = imdilate(BW, se);
    
    % Create masked image.
    maskedImage = I;
    maskedImage(~BW) = 0;
    
    % write images
    % this assumes all input images are .jpg or .png; add cases as needed
    fnamenoext = regexprep(baseFileName,'(.jpg$)|(.png$)','');
    % build filename out of old filename, k, and specified path/extension
    FileName = fullfile(outFolder,sprintf('%s_masked%s',fnamenoext,outfiletype))
    imwrite(maskedImage,FileName); %B is the output images
end

See also:

https://www.mathworks.com/matlabcentral/answers/340928-loading-in-multiple-image-files-of-different-sizes

[Jenifer NG]

Thank so much. I understand

I = mono(I,'y'); this mono function is not defined

[Image Analyst]

Try

if size(I, 3) == 3
    I = rgb2gray(I);
end

[Jenifer NG]

It work fine thanks,

If i want to extract largest blob? Is there any fuction ?

[Image Analyst]

BW = bwareafilt(BW, 1); % Keep largest blob only.

[DGM]

Oh sorry. I meant to delete that. You should be able to use the im2gray() line that's commented out.

I used mono() since I'm using an older version that doesn't have im2gray().

Answer 2

[Image Analyst]

"How can I put process for multiple image ? " << See the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files?