Relational operators and Mat in OpenCV

Mat is a common structure used in OpenCV to store two and higher dimensional data. It is a derivation of the internal Array structure. A relational operator can applied between two Mat objects or a Mat object and a scalar, and the result is a 8-bit single-channel Mat.

Any of these operations is nothing but a call to compare function. This results in a per-element comparison of the Mat. The key information to remember is that for every element whose result is true, the value in the result Mat is set to 0xFF, that is 255. If result is false, it is set to 0. This behavior is so that the resulting Mat can be used as a mask image if needed for other operations.

The operators that are supported are equal, not-equal, greater, greater-or-equal, lesser and lesser-or-equal.

Example usage of such operations:

cv::Mat m0, m1;
cv::Mat m2(m0 == 0);
m2 = m0 > m1;
m2 = m1 <= m0;
m2 = m1 != 1;

Difference between == and is in Python

if i == j:
    # Do something
if i is j:
    # Do something

== operator checks the values behind the two names. It returns True if the two values are equal, False otherwise.

is operator checks the objects behind the two names. It returns True if both the names refer to the same object, False otherwise.

Tried with: Python 3.2

PowerShell: Output Redirection Operators

The output redirection operators > and >> work in PowerShell just like they do in any other shell. > overwrites a file while >> appends to the file.

These output redirection operators are just aliases for the Out-File cmdlet. The equivalent invocations for > and >> are Out-File and Out-File -Append

Tried with: PowerShell 2.0