\begin{tikzpicture}[auto, on grid, scale=.5, y=-1cm, every node/.style={scale=.5, y=-1cm}]
  \def\BlockSize{4}
  \tikzstyle{TextStyle}=[text centered, scale=1/.5, font=\footnotesize]

  \tikzstyle{PU}          =[draw, minimum height=\BlockSize cm, minimum width=\BlockSize cm]
  \tikzstyle{Neighbour}   =[draw, minimum height=1 cm,          minimum width=\BlockSize cm, fill=gray!60]



  \tikzstyle{PixelAnchor}       =[xshift=.5cm, yshift=-.5cm]
  \tikzstyle{Pixel}             =[circle, thin, fill=TikZColorFill, inner sep=0, minimum size=10pt]

  \tikzstyle{PixelNeighbour}    =[Pixel, fill=black!70]
  \tikzstyle{Arrow}             =[-latex,thick, draw=black]
  \tikzstyle{NeighbourSquares}  =[fill=TikZColorFillDark]

  \tikzstyle{EllipseDup}  =[PixelAnchor, draw, ellipse, minimum width=5cm, minimum height=.7cm, inner sep=0]

  \draw[Pixel] (0,0) grid ++(4.5,4.5);
  \node[NeighbourSquares, anchor=north west, minimum width=1cm, minimum height=1cm] at (-1,-1) {};
  \node[NeighbourSquares, anchor=north west, minimum width=4cm, minimum height=1cm] at (0,-1) {};
  \node[NeighbourSquares, anchor=north west, minimum width=4cm, minimum height=1cm] at (4,-1) {};
  \node[NeighbourSquares, anchor=north west, minimum width=1cm, minimum height=4cm] at (-1,0) {};
  \node[NeighbourSquares, anchor=north west, minimum width=1cm, minimum height=4cm] at (-1,4) {};

  % Pixels
  \foreach \x in {0,...,3}
  \foreach \y in {0,...,3}
  {
    \node at (\x,\y) [PixelAnchor,Pixel]() {};
  }

  \path[PixelAnchor, Arrow, shorten >= 2pt] (-1,1) -- ++( 2, 0 );
  \path[PixelAnchor, Arrow, shorten >= 2pt] (4,1)  -- ++( -3, 0 );

  \path[PixelAnchor, Arrow, shorten >= 2pt] (1,-1) -- ++( 0, 2 );
  \path[PixelAnchor, Arrow, shorten >= 2pt] (1,4)  -- ++( 0, -3 );


  \node[EllipseDup] at (1,4) {};
  \node[EllipseDup, rotate=90] at (4,1) {};

  \foreach \y in {-1,...,7}
  {
    \node at (-1,\y) [PixelAnchor,PixelNeighbour]() {};
  }
    \foreach \y in {-1,...,3}
  {
    \node at (4,\y) [PixelAnchor,PixelNeighbour]() {};
  }

%   \path[PixelAnchor, Arrow, dashed, shorten >= 3pt] (4,-1) -- ++( 0 , \BlockSize );
%   \path[PixelAnchor, Arrow, dashed, shorten >= 3pt] (-1,4) -- ++( \BlockSize, 0 );
  \foreach \x in {0,1,...,7}
  {
    \node at (\x,-1) [PixelAnchor,PixelNeighbour]() {};
  }
  \foreach \x in {0,1,...,3}
  {
    \node at (\x,4) [PixelAnchor,PixelNeighbour]() {};
  }

  \node[TextStyle] at (1.2,-1.3) {$p_1$};
  \node[TextStyle] at (4.2,-1.3) {$p_2$};

  \node[TextStyle] at (5.3,1.3) {$p'_2$};

  \node[TextStyle] at (-1.3,1.3) {$p_3$};
  \node[TextStyle] at (-1.3,4.3) {$p_4$};

  \node[TextStyle] at (1.2,5.3) {$p'_4$};





  \path[Arrow, very thick, -] (-1,4) -- ++(6,0);
  \path[Arrow, very thick, -] (4,-1) -- ++(0,6);
  \path[Arrow, very thick, -] (-1,0) -- ++(1,0);
  \path[Arrow, very thick, -] (0,-1) -- ++(0,1);
  \path[Arrow, very thick, -] (0,0) -- ++(4,0);
  \path[Arrow, very thick, -] (4,0) -- ++(4,0);
  \path[Arrow, very thick, -] (0,0) -- ++(0,4);
  \path[Arrow, very thick, -] (0,4) -- ++(0,4);
%   \node[TextStyle] at (-1.2,-1.5) {Top-left};

  \node[TextStyle, anchor=south west, align=left, text width=4cm]                at (-3,10)  (RefLabel)  {Reference pixels};
  \node[TextStyle, anchor=south west, align=left, text width=4cm, below=.5cm of RefLabel]    (PredLabel) {Predicted pixels};
%   \node[TextStyle, anchor=south west, align=left, text width=4cm, right=4cm of RefLabel]     (PixelDup)  {Pixel duplication};
%   \node[TextStyle, anchor=south west, align=left, text width=4cm, below=.5cm of PixelDup]    (PredDir)   {Prediction reference};
  \node[TextStyle, anchor=south west, align=left, text width=4cm, right=4cm of RefLabel]    (PredDir)   {Prediction reference};

  \node[Pixel,        , minimum size=12pt, left=.1 cm of PredLabel.west]  {};
  \node[PixelNeighbour, minimum size=12pt, left=.1 cm of RefLabel.west]   {};
%   \path[Arrow, latex-, dashed] (PixelDup.west) -- ++(-1,0);
  \path[Arrow, latex-] (PredDir.west) -- ++(-1,0);


%   \path[PixelAnchor, Arrow, blue] (2.75,-1) -- ++( -2 , \BlockSize );

\end{tikzpicture}