How to create user defined function in matlab?

I have use below set of code frequently. So i have to make user defined function

below is my frequently used code:-

            x=xvalue;
            y=yvalue;

            for j=1:3;
                red(j)=RGB(y,x,j);
            end
            shape.color=red;

[Azzi Abdelmalek]

Can you explain what are the argument (inputs and outputs) of your function?

[saravanakumar D]

input is x and y values

output is pixel color value -->shape.color= [242 0 12]

Answer 1

[Image Analyst]

I think this is the minimum necessary:

function shape = myFunction(RGB, xvalue, yvalue, i)
  x=xvalue;
  y=yvalue;
  for j=1:3;
    red(j)=RGB(y,x,j);
  end
  shape(i).color=red;

Optionally, x, y, and red could also be outputs, and shape could also be an input. Be aware that the "red" variable actually contains the red, green, and blue values from the pixel at (y, x).

[saravanakumar D]

You didn't store the result value in to variable shape, then how it gives output?

[saravanakumar D]

Is below code is correct? And i don't need i, so i neglect

function shape = myFunction(RGB, xvalue, yvalue)
  x=xvalue;
  y=yvalue;
  for j=1:3;
    red(j)=RGB(y,x,j);
  end
  shape.color=red;
  shape=shape.color;

[Walter Roberson]

No, the last line is wrong. You cannot have two assignments in a single expression.

[saravanakumar D]

I edited now.

[Walter Roberson]

shape.color=red;

creates "shape" as a structure with a field "color" that it sets to the content of "red". Then your statement

shape=shape.color

overwrites "shape" with the contents of the field "color", into which you had written the content of "red". The net effect of your code is as the same as if you had changed those last two lines to

shape = red;

[Image Analyst]

Do you want a structure or not? If there is only one field, then I see no reason at all to use a structure. Just use a simple variable.

Answer 2

[Walter Roberson]

function shape = myFunction(RGB, xvalue, yvalue, i)
  shape(i).color = squeeze(RGB(xvalue, yvalue, :));

[saravanakumar D]

which is output variable shape or shape(i).color?

[Walter Roberson]

The output variable is "shape", as listed in the function header. The "shape" that is output will be a structure array with a single field "color", with the "i"th element of the structure array populated with meaningful data and the rest of the shape(K).color will be the empty array []