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

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

  \def\TikZColorFill{gray!20}
\def\TikZColorFillDark{gray!80}

  \tikzstyle{PixelAnchor}       =[xshift=.5cm, yshift=-.5cm]
  \tikzstyle{Pixel}             =[circle, thin, fill=lightgray, inner sep=0, minimum size=10pt]
  \tikzstyle{PixelNeighbour}    =[Pixel, fill=black!80]
  \tikzstyle{Arrow}             =[-latex,thick, draw=black]
  \tikzstyle{NeighbourSquares}  =[fill=darkgray!80]


  \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]() {};
  }
  \foreach \x in {-1}
  \foreach \y in {-1,...,7}
  {
    \node at (\x,\y) [PixelAnchor,PixelNeighbour]() {};
  }
  \foreach \x in {0,1,...,7}
  \foreach \y in {-1}
  {
    \node at (\x,\y) [PixelAnchor,PixelNeighbour]() {};
  }


  \path[PixelAnchor, Arrow, dashed, shorten >= 38 pt] (.5,-1) -- ++( -2 , \BlockSize );
  \path[PixelAnchor, Arrow,         shorten >= 25 pt] (1,-1) -- ++( -2 , \BlockSize );
  \path[PixelAnchor, Arrow, dashed, shorten >= 13 pt] (1.5,-1) -- ++( -2 , \BlockSize );
  \foreach \x in {2,...,5}
  {
    \path[PixelAnchor,Arrow] (\x,-1) -- ++(-2, \BlockSize);
  }
  \foreach \x in {2.5,...,4.5}
  {
    \path[PixelAnchor,Arrow,dashed] (\x,-1) -- ++(-2, \BlockSize);
  }

  \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) node[midway,above, yshift=1cm, scale=1.2] {Top};
  \path[Arrow, very thick, -] (4,0) -- ++(4,0) node[midway,above, yshift=1cm, scale=1.2] {Top-right};

  \path[Arrow, very thick, -] (0,0) -- ++(0,4) node[midway,above, xshift=-1cm, scale=1.2, rotate=90] {Left};
  \path[Arrow, very thick, -] (0,4) -- ++(0,4) node[midway,above, xshift=-1cm, scale=1.2, rotate=90] {Bottom-left};
%   \path[Arrow, very thick, -] (8,0) -- ++(0,-1);
%   \path[Arrow, very thick, -] (0,8) -- ++(-1,0);

  \node[anchor=south west, align=left, text width=4cm]                at (6,6)     (RefLabel)  {Reference pixels};
  \node[anchor=south west, align=left, text width=4cm, below=.5cm of RefLabel]     (PredLabel) {Predicted pixels};
  \node[anchor=south west, align=left, text width=4cm, below=.5cm of PredLabel]    (PredDir)   {Prediction direction};

  \node[Pixel,          left=1.3 cm of PredLabel]  {};
  \node[PixelNeighbour, left=1.3 cm of RefLabel]   {};
  \path[Arrow, latex-] (PredDir.west) -- ++(-1,0);


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

\end{tikzpicture}