Sending image as argument from C# to matlab function

Question

I'm trying to call a MATLAB function from C# using MLApp class, feval function specifically.

Since I'm a beginner I looked through the internet and found help calling MATLAB functions. I just simply called a MATLAB function which takes two integers as input and MATLAB returns sum and difference correctly. But the reason I really need to do this is to send an image to MATLAB function and perform some analysis.

So far I haven't been able to find anything helpful over the internet. Can this class be used to pass images to MATLAB function if so, how? If not what other ways are there?

MATLAB

function [x,y] = myfunc(a,b) 
  x = a + b; 
  y = a-b;

C#

MLApp.MLApp matlab = new MLApp.MLApp();
matlab.Execute(@"cd 'D:\Program Files\MATLAB\MATLAB Production Server\R2015a\bin'");
object result = null;
matlab.Feval("myfunc", 2, out result, 3, 2);
object[] res = result as object[];
Console.WriteLine(res[0]);
Console.WriteLine(res[1]);
Console.ReadLine();

Answer 1

An easy way would be to save the image to disk from your C# application, then call MATLAB (using COM Automation as you've shown) to evaluate your image processing function by passing it the file name as a string. The MATLAB function would simply load the image by name, process it, and save the result as another image. Then return the path to the output image from your MATLAB function to C#, which finally reads it on its own..

So in C# you would do something like:

static void Main(string[] args) 
{
    var img = ...;  // image data
    string input_image = @"C:\path\to\image.png";
    save_image(img, input_image);    // save your image to disk

    MLApp.MLApp matlab = new MLApp.MLApp(); 
    object result = null; 
    matlab.Feval("my_processing_func", 1, out result, image); 
    object[] res = result as object[]; 
    string output_image = (string) res[0];

    var img_processed = load_image(output_image);  // load image from disk
} 

On the MATLAB side, the function does something like:

function out_fname = my_processing_func(in_fname)
    % read input image
    img = imread(in_fname);

    % ... apply some image processing functions
    img = process(img);

    % write resulting image to disk
    out_fname = [tempname() '.png'];
    imwrite(img, out_fname);
end

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You could also pass data between C# and MATLAB COM server using PutFullMatrix and GetFullMatrix functions. The image would simply be a matrix of numeric values. Just remember that MATLAB stores array in column-major order.

Here is a sample code that shows how to retrieve variables from MATLAB workspace in C#: https://stackoverflow.com/a/21123727/97160

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A third option would be to use the MATLAB Compiler SDK toolbox. This lets you compile/package your MATLAB functions into a .NET assembly that can be used on machines without MATLAB (requires the MCR runtime).