如何从图像和识别位置中删除特定颜色？

Question

I have an image as .png , i want to do following tasks with given image :

1 - Remove unnecessary White shade from image.

2 - Identify positions/coordinates of big black point in image.

For Task 1 my attempt is:

img = imread('1.png');
imshow(img);
I = img;
[r c] = size(I);
for i=1:r
    for j=1:c
        if I(i,j) > 230 %here i am changing 240 to different values to get result 
            %but this is just some hack
            I(i,j) = 0;
        end
    end
end
imshow(I);

Where Original Image is :

And Matlab results are :

And for (2) i am out of ideas how can i do that any help appreciated.

Note: I am new in image processing, so kindly explain me in easy way so i can understand. thanks

Answer 1

For task 1, I am not entirely sure what you mean by "removing", from your code, I guess you would like to set the pixel values to 0. A simpler and faster method would be:

img = imread('1.png');
img(img>230)=0;

This code sets all the values of img that are higher than 230 to zero. img>230 creates a logical array with the size of img, true for elementes higher than 230, and false for others. Then this logical array is used to set those pixels to 0. (But you could do anything you want with them)

Matlab was designed to do operations on vectors and matrices, looping through the elements is usually much slower.

For task 2, maybe look into this: http://nl.mathworks.com/help/images/examples/detect-and-measure-circular-objects-in-an-image.html