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I use pgfplots to draw a black-white array resembling imshow() in MATLAB.

I use the following code (from Plot a matrix of real values with TikZ/PGF like imshow in matlab ) to do it

    \begin{axis}[x=4mm,y=4mm,xtick=\empty,ytick=\empty,colormap={bw}{gray(0cm)=(0); gray(1cm)=(1)}]
    \addplot[scatter,scatter src=explicit,
             only marks, mark=square*,mark size=2mm]
             table[x=x,y=y,meta=l] {datafile.txt};

But if the blocks are all black, the boundary line between them disappears. I want the boundary line to be more apparent. How can I do that?

I have problem posing image, see

enter image description here

for an example.

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closed as too localized by percusse, Jake, Joseph Wright Jun 12 '12 at 21:05

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Could you include an example of what your datafile looks like? – Jake May 12 '12 at 8:38
Do you want the line to be white, or gray, or some other colour? – Jake May 21 '12 at 9:01
@Jake Do you think it's time we close this one? – percusse Jun 12 '12 at 15:45
@percusse: Yes, I think so. There'd be too much speculation required for an answer, and if anyone needs this later on, they can just ask a new question. – Jake Jun 12 '12 at 15:55
@Jake Voted as TL. – percusse Jun 12 '12 at 15:59

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