Why do I get "Array indices must be positive integers or logical values." Image processing.

Please help me. I dont know what I doing wrong...

clear all, clc 
    
    [Iwe, map] = imread('chest-xray_2','bmp');
    figure(1)
    image([Iwe,map]);
    title("oryginal image")
    
    colormap(map);
    Iwe=double(Iwe);
    [row col deep]=size(Iwe);
    
    IweR=Iwe(:,:,1);
    IweG=Iwe(:,:,2);
    IweB=Iwe(:,:,3);
    
    
    Iwe_grey(:,:,1)=(IweR+IweG+IweB)/3;
    Iwe_grey(:,:,2)=Iwe_grey(:,:,1);
    Iwe_grey(:,:,3)=Iwe_grey(:,:,1);
    Iwe_grey=Iwe_grey(:,:,1);
    
    figure(2)
    imshow(Iwe_grey);
    title("monochrome image");
    Iwe_grey=uint8(Iwe_grey);
    
    %%started histogram
    histogram = zeros(256,1);
    for y=1:col
        for x=1:row
         b=Iwe_grey(x,y)+1;
         histogram(b+1)=histogram(b+1)+1;
    
        end
    end
    
    figure(3)
    bar(histogram);
    %%stacked histogram
    cumulative(1)=histogram(1)
    for z=2:256
        cumulative(z)=cumulative(z-1)+histogram(z)
    end
    
    cumulative = cumulative'
    
    %%aligned histogram
    for z=1:256
            hist_norm(z) = (256*cumulative(z)/cumulative(256));
    end
    
    figure(4)
    plot(hist_norm);
    title('aligned histogram')
    
    for x=1:row
        for y= 1:col
            if(Iwe_grey(x,y)<0)
               Image_out_grey(x,y)=0;
            else if (Iwe_grey(y,x) > 255)
                else Image_out_grey(y,x)=255*cumulative(Iwe_grey(y,x))/cumulative(255);
                end;
            end;
        end;
    end;
    
    Image_out_grey = uint8(Image_out_grey);
    figure(5)
    imshow(Image_out_grey);
    title("the resulting image after aligning the histogram");
    
    

Answer 1

[Cris LaPierre]

You get that error because any time you use indexing to extract values from a variable, the index number must be integers >= 1. Somewhere in your code (you did not indicate where) you are using an invalid index.

% Good
A=[1:10];
A(3)

ans = 3

% Bad
A(4.3)

Array indices must be positive integers or logical values.

[Tomasz Jednorowski]

hello thanks a lot for the quick response.

Here I am using the wrong index, at the same time I am not able to understand how to improve it.

Error in untitled (line 74)

else Image_out_grey (y_col, x_row) = 255 * cumulative (Iwe_grey (y_col, x_row)) / cumulative (255);

>>

[Cris LaPierre]

First, identify where you are indexing, and then see if the values being used are integers or not.

Here, I suspect the values in Iwe_grey are not.

[Tomasz Jednorowski]

Thank U very much! Luckily I won with the problem. Correct code:

clear all, clc

[Iwe, map] = imread('chest-xray_2','bmp');

figure(1)

image([Iwe,map]);

title("Obraz oryginalny")

colormap(map);

Iwe=double(Iwe);

[row col deep]=size(Iwe);

IweR=Iwe(:,:,1);

IweG=Iwe(:,:,2);

IweB=Iwe(:,:,3);

Iwe_grey(:,:,1)=(IweR+IweG+IweB)/3;

Iwe_grey(:,:,2)=Iwe_grey(:,:,1);

Iwe_grey(:,:,3)=Iwe_grey(:,:,1);

Iwe_grey=Iwe_grey(:,:,1);

figure(2)

Iwe_grey=uint8(Iwe_grey);

imshow(Iwe_grey);

title("Obraz monochromatyczny");

%%histogram

histogram = zeros(256,1);

for y_col=1:col

for x_row=1:row

if Iwe_grey(x_row,y_col)>0 && Iwe_grey(x_row,y_col)<=255

b=Iwe_grey(x_row,y_col);

histogram(b)=histogram(b)+1;

end

end

end

figure(3)

bar(histogram);

%obliczanie histogramu skumulowanego

cumulative=histogram;

for z_hist=2:256

cumulative(z_hist)=cumulative(z_hist-1)+histogram(z_hist);

end

figure(4)

plot(cumulative);

title('histogram skumulowany')

Iwe_grey=uint8(Iwe_grey);

for x_row=1:row

for y_col= 1:col

if(Iwe_grey(x_row,y_col)<=0)

Image_out_grey(x_row,y_col)=0;

else if (Iwe_grey(x_row,y_col) >= 255)

Image_out_grey(x_row,y_col)=255;

else Image_out_grey(x_row,y_col)=(255*cumulative(Iwe_grey(x_row,y_col)))/cumulative(255);

end;

end;

end;

end;

Image_out_grey = uint8(Image_out_grey);

figure(5)

imshow(Image_out_grey);

title("Obraz wynikowy po wyrównaniu histogramu ");