'**SUMMARY**
Find the index of the first element of the linescan that has
a value equal to value. If nothing is found None is returned.
**PARAMETERS**
* *value* - the value to look for.
**RETURNS**
The first index where the value occurs or None if none is found.
**EXAMPLE**
>>>> ls = img.getLineScan(x=10)
>>>> idx = ls.findFIRSTIDXEqualTo()'

def findFirstIdxGreaterThan(self, value=255):

    vals = np.where((np.array(self) >= value))[0]
    retVal = None
    if (len(vals) > 0):
        retVal = vals[0]
    return retVal
