ipa: simple: blc: Use 16 as starting blacklevel when there is no sensor-info

At the moment the blc code uses 255 as starting blacklevel for sensors
where there is no blacklevel info in the sensor-helper.

There are a number of issues with this:

1. When the first frame is bad (e.g. mostly white) which happens sometimes
the initial blacklevel will be kept leading to a divide by zero problem
in the AGC code (this divide by 0 problem is avoided in the AGC code by
not running the AGC algorithm).

2. Not runnning the AGC algorithm means that the gain/exposure do not
change, which causes the BLC algorithm to not run on the next frames,
so we keep the bad 255 blacklevel which stops AGC from running which
stops BLC from running. Leaving things stuck at a 255 blacklevel
resulting in an unusuable image.

3. Sometimes the auto-blc code leads to an unrealistic high
blacklevel detection which results in lower image quality.

To fix this start with a blacklevel of 16, which is the highest
(4096 / 256) blacklevel used for any sensor listing a blackLevel_
value in the sensor-helper class.

Note 2. could alternatively be fixed by disabling the check for
exposure/gain changes when the blacklevel is unrealistic high,
but that still leaves the other problems.

Signed-off-by: Hans de Goede <hansg@kernel.org>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/simple/algorithms/blc.cpp

@@ -43,7 +43,7 @@ int BlackLevel::configure(IPAContext &context,
 	if (definedLevel_.has_value())
 		context.configuration.black.level = definedLevel_;
 	context.activeState.blc.level =
-		context.configuration.black.level.value_or(255);
+		context.configuration.black.level.value_or(16);
 	return 0;
 }