Improper assignment with rectangular empty matrix., how to solve ?

hey everyone

please i am getting this error :

Improper assignment with rectangular empty matrix on this line :

midpoints1(k) = (leftEdge1 + rightEdge1)/2;

how can i solve that ? any help is appreciated, thanks

for k=700:800

   oneRow1 = binaryImage(k, :);

   leftEdge1 = find(oneRow1, 1, 'first');
   rightEdge1 = find(oneRow1, 1, 'last');

   hold on;

   midpoints1(k) = (leftEdge1 + rightEdge1)/2;

   plot(leftEdge1, k, 'rx','LineWidth',2);
   plot(rightEdge1, k, 'rx','LineWidth',2);

   plot(midpoints1(k), k, 'yx','LineWidth',2);

end

X1=(700:800);
midpoints1=midpoints1(midpoints1~=0);
new_x1 = linspace(500, 900);
coeffs1 = polyfit(X1, midpoints1, 1);
new_y1 = polyval(coeffs1, new_x1);
plot(new_y1,new_x1, '-','LineWidth',2);

[Matt J]

When you use the debugger to stop at this line right before the error occurs, what are the dimensions of midpoints1, leftEdge1 and rightEdge1 at that point?

[mounim]

when i break the code at that line, the :

• leftEdge1 = [ ]
• rightEdge1 = [ ]
• midpoints = 1x51 double

what i am trying to do is scanning different pictures, to finde the edge, not all the pictures give me the error, but som do !

in the pictures where i do not get the error, the leftEdge1 and rightEdge1 are single values.

what should i change to not get that error ? to not store empty values ?

[Walter Roberson]

What behavior would seem appropriate to you on rows that have no 1 in them ?

[mounim]

well, the most appopriate is just to ignore that row, and go on.

[Walter Roberson]

Read the documentation for isempty()

What value do you want stored in midpoints1(k) in this situation?

[mounim]

it have to just store a zero ( a black pixel ), i tried this code, but it is not working 100% still gives me errors:

if isempty(midpoints1(k)) then
    midpoints1(k)== 0;
end

this one not working neither

if isempty(midpoints1(k)) then
    midpoints1(k)= zeros(size(midpoints1(k)));
end

Answer 1

[Walter Roberson]

In some rows, there are no 1's. When that happens, the results of find() are empty. You are trying to store the midpoint of that empty range into midpoints1(k), which requires a location which is a 1x1 value not a 0 x 0 value.

[Walter Roberson]

if isempty(leftEdge1)
  midpoint1(k) = 0;
else
  midpoints1(k) = (leftEdge1 + rightEdge1)/2;
  %and do the plotting here
end