use Y0 to get grey-value from YUV-data

CID:27906
checking dynamic_cast result, can lead to dead-code

CID:27833
locking mutex before accessing 'isrunning'

CID:27891
fixed typo (missing semicolon)
mark seemingly dead-code as false-positives

CID:27847
set average to 0 if there are no elements

CID:27850,27851,27852,27853,27854,27855,27856,27857,27858,27859
no need to check return-value of props.get()

CID:27804
check whether we actually do have the named property

CID:27801
check return value of (x)ioctl

CID:27799
initialize member variables

CID:27953
initialize member variables

CID:27960
removing unused variables
indentation
sanitizing image dimensions

CID:27947,27876
mark unset default by using negative values

CID:27835
initializing structs to 0

CID:27983
simplifying printout code

CID:27838
disable canvas-evaluation

- there's a double-assignment to canvas (bug!)
- it's not used anyhow

CID:27865,28028
simplify colormask code

using a function that sets the glColorMask selected via an enum

CID:27841,27842
mark dead-code as intentional

CID:27846,27843