\newcommand{\scale}{.4}
\begin{tikzpicture}[auto, on grid, scale=\scale]
  \def\BlockSize{8}
  \tikzstyle{TextStyle}=[text centered, font=\Huge]

  \tikzstyle{PU}          =[draw, scale=\scale, minimum height=\BlockSize cm, minimum width=\BlockSize cm, font=\Huge]
  \tikzstyle{Neighbour}   =[draw, scale=\scale, minimum height=1 cm,          minimum width=\BlockSize cm, font=\Large, fill=gray!60]
  \tikzstyle{Arrow}       =[-latex,thick, draw=black]
  \tikzstyle{Pixel}           =[circle, rounded corners ,fill=lightgray, thick,  scale=0.3]
  \tikzstyle{PixelNeighbour}  =[Pixel, fill=gray]

  \node[PU, anchor=north west] at (0,0) { }; % PU
%   \node[Neighbour, anchor=south west]                   at (0,0)            { top };        % Top
%   \node[Neighbour, anchor=south west]                   at (\BlockSize,0)   { top-right };  % Top-right
%   \node[Neighbour, anchor=south east, rotate=90]        at (0,0)            { left };       % Left
%   \node[Neighbour, anchor=south east, rotate=90]        at (0,-\BlockSize)  { bottom-left }; % Bottom-left
%   \draw[Neighbour, scale=1/\scale] (0,0) rectangle ++(-1cm,1cm);


  % Pixels
  \foreach \x in {0,1,...,7}
  \foreach \y in {-1,...,-8}
  {
    \node at (\x+0.5,\y+0.5) [Pixel]() {};
  }
  \foreach \x in {-1}
  \foreach \y in {0,...,-9}
  {
    \node at (\x+0.5,\y+0.5) [PixelNeighbour]() {};
  }
  \foreach \x in {0,1,...,12}
  \foreach \y in {0}
  {
    \node at (\x+0.5,\y+0.5) [PixelNeighbour]() {};
  }

  \path[Arrow, shorten >= 48 pt] (1+.5,.5) -- ++( -3 , -\BlockSize );
  \path[Arrow, shorten >= 25 pt] (2+.5,.5) -- ++( -3 , -\BlockSize );
  \foreach \x in {3,...,10}
  {
    \path[Arrow] (\x +.5,.5) -- ++(-3, -\BlockSize);
  }
  \node at (15,-6) [scale=.4] (PredLabel) {Predicted Pixels};
  \node[below=.3cm of PredLabel, scale=.4] (RefLabel) {Reference Pixels};
  \node[Pixel, left=.8 cm of PredLabel] (Pred) {};
  \node[PixelNeighbour, left=.8 cm of RefLabel] (Ref) {};



\end{tikzpicture}