on this page: http://docs.opencv.org/doc/user_guide/ug_mat.html

There are two places where "texttt{" is visible (typos)

furthermore in the section "Visualizing images",
in the example code, this line:

<pre>
sobelx.convertTo(draw, CV_8U, 255.0/(maxVal - minVal), -minVal);
</pre>

should become:

<pre>
sobelx.convertTo(draw, CV_8U, 255.0/(maxVal - minVal), -minVal*255.0/(maxVal - minVal));
</pre>