Trying to send big data throug serial ports and Arduino

Hi!

I am trying to send some data (actually the elements of an 400x600x3 matrix which I read from a jpg image) from matlab to an Arduino, and the Arduino should send it back to the PC so I could read it out from the serial port. On the Arduino I wired together the IO ports 0-1 (these are for serial communications). It works fine for a few characters but when I try to send bigger matrices I get an error:

Warning: Unsuccessful read: The specified amount of data was not returned within the Timeout period.. Assignment has more non-singleton rhs dimensions than non-singleton subscripts.

I have no idea how to move on, please can someone help me? Thanks a lot.

Matlab code:

arduinoCom = serial('COM15', 'BaudRate', 9600);
arduinoCom.Terminator = ('');
fopen(arduinoCom);

A = imread('img_lights.jpg');
[row, col, dim] = size(A);

for i=1:row
    for j=1:col
        for k=1:dim
            strSend = char(A(i,j,k));
            fprintf(arduinoCom, strSend);
            B(i,j,k) = fread(arduinoCom, 1);
        end
    end
end

Arduino code:

void setup() {
  Serial1.begin(9600);
  Serial.begin(9600);
}

void loop() {
char a; char b;

    if(Serial.available()){
      Serial1.write(Serial.read());
    }

    if(Serial1.available()){
    Serial.write(Serial1.read());

    }
}