% contents of matrix.txt
x   y   v
0   0   78
1   0   63
2   0   42
3   0   51
4   0   99
...

% MWE
documentclass{standalone}
usepackage[utf8]{inputenc}
usepackage{ifthen}
usepackage{tikz}
usepackage{pgfplots}

usetikzlibrary{positioning}

begin{document}
    begin{tikzpicture}
        begin{axis}[enlargelimits=false, axis lines=none, colormap/blackwhite]
            addplot [
                matrix plot,
                visualization depends on={value ifthenelse{thisrow{v} < 90}{white}{black} as tcolor},
                nodes near coords,
                scatter/@pre marker code/.append style={/tikz/text=tcolor},
                mesh/cols=8,
                point meta=explicit,
                ] table [x=x, y=y, meta=v] {matrix.txt};
        end{axis}
    end{tikzpicture}
end{document}