%User Variables
\usetikzlibrary{calc,trees,positioning,arrows,chains,shapes.geometric}
\usetikzlibrary{decorations.pathreplacing,decorations.pathmorphing,shapes}
\usetikzlibrary{matrix,shapes.symbols,plotmarks,decorations.markings,shadows}

\newcommand{\block}{1cm}
\newcommand{\scale}{0.7}

\begin{tikzpicture}[scale=\scale,every node/.style={minimum size=0.6*\scale*\block}, inner sep=0pt,on grid]

	\definecolor{lightgray}{rgb}{0.80,0.80,0.80};
	\definecolor{darkgray}{rgb}{0.40,0.40,0.40};

	\tikzstyle{arrow}=[draw, <->,shorten <=1pt,shorten >=1pt,>=stealth',thick]
	\tikzstyle{pel}=[circle, rounded corners ,draw=lightgray!80, fill=lightgray!80, thick,  scale=0.5]
	\tikzstyle{outerpel}=[pel, fill=gray, draw=gray!90, thick]
	\tikzstyle{innerpel}=[pel, fill=black!90, draw=black!90, thick]

	% Image pixels
	\foreach \x in {-2,-1,0,1,3,4,5,6}
	\foreach \y in {-2,-1,0,1,3,4,5,6}
	{
		\node at (\x+0.5,\y+0.5) [pel] {};
	}

  \node at (2.5,4) [] {...};
  \node at (2.5,5.5) [] {...};
  \node at (2.5,1) [] {...};
  \node at (2.5,-.5) [] {...};

  \node at (-.5,2.5) [rotate=90] {...};
  \node at (1,2.5) [rotate=90] {...};
  \node at (5.5,2.5) [rotate=90] {...};
  \node at (4,2.5) [rotate=90] {...};


	% outer boundary
	\foreach \x in {0,1,3,4}
	\foreach \y in {-1,5}
	{
		\node at (\x+0.5,\y+0.5)  [outerpel](ref_tp)  {};
	}
	\foreach \x in {-1,5}
	\foreach \y in {0,1,3,4}
	{
		\node at (\x+0.5,\y+0.5)  [outerpel](ref_tp)  {};
	}

	% inner boundary
	\foreach \x in {0,1,3,4}
	\foreach \y in {0,4}
	{
		\node at (\x+0.5,\y+0.5)  [innerpel](ref_tp)  {};
	}
	\foreach \x in {0,4}
	\foreach \y in {0,1,3,4}
	{
		\node at (\x+0.5,\y+0.5)  [innerpel](ref_tp)  {};
	}


;
	\node[anchor=center,scale=\scale, text centered] at (2.5,2.5) {Lost Block};

	\draw[draw=black, thick] (0*\block,-1) -- ++(0,7*\block);
	\draw[draw=black, thick] (5*\block,-1) -- ++(0,7*\block);
	\draw[draw=black, thick] (-1*\block,0*\block) -- ++(7*\block,0);
	\draw[draw=black, thick] (-1*\block,5*\block) -- ++(7*\block,0);


	\node[anchor=west,scale=\scale] at (-3,7.1) (pixel_label) {Pixel};
	\node at (-1.6,5.35) (pel) {};
	\path [-latex,anchor=center] (pixel_label) edge (pel);

	\node[anchor=west,scale=\scale, text centered] at (.5,-2.2) (inner_pixel_label) {Internal Boundary};
	\node at (2-0.4,0.6) (inner_pel) {};
	\path [-latex,anchor=center] (inner_pixel_label) edge (inner_pel);



	\node[anchor=west,scale=\scale, text centered] at (5,7.2) (outer_pixel_label) {External Boundary};
	\node at (6-0.5,4.4) (outer_pel) {};
	\path [-latex,anchor=center] (outer_pixel_label) edge (outer_pel);

	\node[anchor=west,scale=\scale, text centered] at (0.1,7.1) (ref_pixel_label) { \Large $f_{(x,y,t)}$ };
	\node at (1.4,5.4) (ref_pel) {};
	\path [-latex,anchor=center] (ref_pixel_label) edge (ref_pel);

	\node[anchor=center,scale=\scale, text centered] at (2.5,6)  (ref_pixel_label) { \Large T };
	\node[anchor=center,scale=\scale, text centered] at (2.5,-1) (ref_pixel_label) { \Large B };
	\node[anchor=center,scale=\scale, text centered] at (-1,2.5) (ref_pixel_label) { \Large L };
	\node[anchor=center,scale=\scale, text centered] at (6,2.5)  (ref_pixel_label) { \Large R };


\end{tikzpicture}