How can i use threshold to convert a gray-scaled image into binary image ?

How can I use threshold to convert a gray-scaled image into binary image , I mean to get the image just black and white ?

Does Binarization help ??

Thx

Answer 1

[Jan]

This is straightforward:

A = imread('cameraman.tif'); % example grayscale image
threshold = 120; % custom threshold value
A_bw = A > threshold;

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edit: removed factor of 255 as Image Analyst pointed out

[Christine Ak]

Thxxxx :d

Answer 2

[Simon]

Hi!

If you load an image into matlab, you get a matrix A (for example) of size (XxYx3) with X and Y being the number of pixels in x- and y-direction. Usually this matrix is for RGB images. Look at imread

If it is a grayscale image the values for all three colors are the same, they range between 0 and 255. You may now apply a threshold

% threshold 
t = 128;
% find values below
ind_below = (A < t);
% find values above
ind_above = (A >= t);
% set values below to black
A(ind_below) = 0;
% set values above to white
A(ind_above) = 255;

[Christine Ak]

Thxxx Alot

Answer 3

[Image Analyst]

Yes you binarize the image by thresholding:

binaryImage = grayImage > thresholdValue;

There is no need to ever multiply by 255 that I've ever encountered. Displaying the binary (logical) image will show it as black and white even without multiplying by, or directly setting to, a value of 255.

[Jan]

Right, in general (and especially for binarized images) the scaling is obsolete...

[Christine Ak]

Thxxx alot

Answer 4

[burçin temur]

how can I change the red band with the green band in image?

[Image Analyst]

[r,g,b] = imsplit(rgbImage);
rgbImage = cat(3, g, r, b);

[burçin temur]

thanks

Answer 5

[Ali nafaa]

x = imread('cameraman.tif');
figure,imshow(x);

[r,c] = size (x);
output=zeros(r,c);

for i = 1 : r
    for j = 1 : c
        if x(i,j) > 128
            output(i,j)=1;
        else
            output(i,j)=0;
        end
    end
end

figure,imshow(output);

[Image Analyst]

Or, without using a for loop

x = imread('cameraman.tif');
output = x > 128; % Or whatever the threshold is chosen to be.

[Ali nafaa]

Undefined variable mask

[Image Analyst]

Sorry, I changed it to x and output like you used. I find it's easier for people to understand the code if you use descriptively named variables. Usually people think of x as like in an x-y graph, not a binary image. So I'd rather use "mask" or "binaryImage" rather than "output", and "grayImage" rather than "x".

[Ali nafaa]

yes thank you