I don't understand why the last line is wrong

sz = size(img);

Unrecognized function or variable 'img'.

out_sz = size(gray);

BinEdges = [0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1];
r = 377;
%ben trai
for ca=0:197
    a = randn(r, ca);
end
figure 
q = histogram(a);

%ben phai
for cb = 198:394
    b = randn(r, cb);
end     
figure
w = histogram(b);

figure 
e = abs(q-w);

[Mathieu NOE]

what error do you get ?

Answer 1

[Rik]

Your syntax is confusing. I don't think this code does what you think it does. The a and B variables are overwritten every iteration, so only the last is used.

The underlying cause is probably that you don't explicitly use the same bins for the two histograms, so the chance they happen to be the same is slim.

Answer 2

[Image Analyst]

Not sure what your goal is, but you can't subtract histogram objects. Perhaps you want to use histcounts() or get a property of your histogram objects. But you need to make sure the arrays are the same size (histograms have the same numbers of bins). So you might need to send in the 'Edges' array to histogram to make sure of that.

img = imread('cameraman.tif');
sz = size(img);
out_sz = size(gray);
BinEdges = [0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1];
r = 377;
%ben trai
for ca=0:197
    a = randn(r, ca);
end
figure 
q = histogram(a)

q = 
  Histogram with properties:

             Data: [377×197 double]
           Values: [1 1 0 2 1 2 2 8 10 14 14 25 42 53 74 87 131 144 196 206 300 377 453 540 584 735 875 1090 1174 1370 1534 1643 1873 2096 2234 2436 2520 2677 2825 2914 2964 3009 2970 2831 2891 … ]
          NumBins: 84
         BinEdges: [-4.2000 -4.1000 -4 -3.9000 -3.8000 -3.7000 -3.6000 -3.5000 -3.4000 -3.3000 -3.2000 -3.1000 -3 -2.9000 -2.8000 -2.7000 -2.6000 -2.5000 -2.4000 -2.3000 -2.2000 -2.1000 -2 … ]
         BinWidth: 0.1000
        BinLimits: [-4.2000 4.2000]
    Normalization: 'count'
        FaceColor: 'auto'
        EdgeColor: [0 0 0]

  Show all properties

%ben phai
for cb = 198:394
    b = randn(r, cb);
end     
figure
w = histogram(b)

w = 
  Histogram with properties:

             Data: [377×394 double]
           Values: [3 3 0 4 1 2 2 0 1 2 5 3 7 10 4 7 12 15 23 15 34 34 42 38 36 71 59 60 68 99 130 114 145 161 167 182 202 249 288 308 359 384 404 458 480 520 627 662 738 868 878 929 967 1024 … ]
          NumBins: 171
         BinEdges: [-4.1000 -4.0500 -4.0000 -3.9500 -3.9000 -3.8500 -3.8000 -3.7500 -3.7000 -3.6500 -3.6000 -3.5500 -3.5000 -3.4500 -3.4000 -3.3500 -3.3000 -3.2500 -3.2000 -3.1500 -3.1000 … ]
         BinWidth: 0.0500
        BinLimits: [-4.1000 4.4500]
    Normalization: 'count'
        FaceColor: 'auto'
        EdgeColor: [0 0 0]

  Show all properties

figure 
e = abs(q-w);

Operator '-' is not supported for operands of type 'matlab.graphics.chart.primitive.Histogram'.