how to mark the highest white pixel through bottom to the top? using grayscale image.

   %point location
row=find(sum(img8,2)==0,1,'last')+1;
col=find(img8(row,:)~=0);
row=row(ones(size(col)));
Points=[row(:) col(:)];
imshow(img8);
hold on
plot(Points(:,2),Points(:,1)','rp','MarkerSize',12)
a=text(Points(1,2),Points(1,1),['This is (col,row)(',num2str(Points(1,2)),',',num2str(Points(1,1)),')']);
set(a, 'FontName', 'Arial' ,'FontWeight', 'bold', 'FontSize', 12,'Color', 'blue');
hold off

[Image Analyst]

What do you mean by highest? The lowest row value? Or the brightest gray level?

[nurul najmah]

means that from the bottom image,I want to find the highest white pixel. or my misunderstanding about the grayscale image do not have fixed white value of pixel?

Answer 1

[Chad Greene]

The white pixels are the ones where all three color components R, G, and B equal 255, so you can get a 2D logical matrix of either white or non-white pixels like this:

I = imread('test.png'); 
white = sum(I,3)==3*255;

The highest white pixel in the image corresponds to the first white pixel in each column, so you can loop through columns going from left to right to find the first white pixel in each column:

row = nan(1,size(white,2)); % preallocates the rows.  
for k = 1:length(row) 
    try
        row(k) = find(white(:,k),1,'first');  
    end
end

imshow(I)
hold on
plot(1:k,row,'b-')

Answer 2

[Stephen23]

Very simply without any loops, using vectorized code:

X = imread('grayscaleImage.png');
[R,C] = find(all(X==255,3));
[Y,Z] = unique(C,'first');
imshow(X);
hold on
plot(C(Z),R(Z),'-rx')

produces this:

[nurul najmah]

it works well.. thank you......

[Stephen23]

My pleasure. You can also vote for answers that work well.

[Chad Greene]

I voted for your answer Stephen!