MATLAB：使用行投影直方图裁剪图像

Question

I am a beginner in Matlab and I am trying to implement a research paper of ANPR Parking System which uses the row projection histogram to identify the horizontal region of the license plates. I have written the following code for calculating the vertical gradients:

Matlab Code:

[rows,cols] = size(img);
img2 = zeros(rows,cols);

%Calculated the gradients
for i =1:1:rows
    for j =1:1:cols-1
        img2(i,j) = abs(img(i,j+1) - img(i,j));
    end
end

% calculated the mean of gradients to determine which pixels hold the value
% that is above the average difference as the paper says `Then the average
% gradient variance is calculated and compared with each other. The bigger
% intensity variations provide the rough estimation of license plate region.`

M = mean2(img2);
for i =1:1:rows
    for j =1:1:cols-1
        if(abs(img(i,j+1) - img(i,j))<M)
            img2(i,j)=0;
        else
            img2(i,j)=100;
        end
    end
end

% Applied average filter to reduce the noise
img2 = filter2(fspecial('average',2),img2)/255;

% Output is shown
figure,imshow(img2);title('Gradient');

After the gradients calculation, I computed the following histogram:

Now I need to crop the license plate according to the criteria given in the paper:

But I don't know how to crop the image on the basis of the horizontal projection histogram?

I have read some Answers on mathworks and stackoverflow but couldn't find any guidance regarding my issue. Someone please guide me what I need to do to crop the horizontal area as shown in the image. Thanks in advance.

Answer 1

The discription says "horizontal projection of vertical gradient" . Did you compute the vertical gradient before computing the projection ?

From the looks of the image i think you might have missed this step from another similar question here .