Share your experience!
Do you use it while a light is switched on? So the auto brightness might set the brightness higher.
I've tried all posible scene and light conditions. 
The phone takes bad/ poor images indoors now.
I crosschecked my very first pictures the week i bought the phone vis-a-vis now, the problems was never there initially. could an upgrade to 4.2.2 firmware be the cause?
While there's a small possibility that your Z display is faulty.
IMHO, what you are experiencing is the Z display's inability to produce true black.
Something TFT LCD is not reknown for.
Unfortunately, the Z display has particularly poor black levels.
This is something we all can expect improved upon in the newer generation Xperia Triluminos models.
And I hope one day when OLED finally finds its way to Xperia.
Like it has in Sony Broadcast Trimaster displays. 
I chose the ZL, for its superior display over Z.
Yet still I was surprised by just how poorly my ZL displayed as a landscape, bedside, alarm clock in a fully dark room. 
It was just far too bright.
Even on the lowest brightness setting, with adapt to lighting conditions enabled.
So I had no choice but to simply switch off my ZL at night.
Instead I rely on my trusty Sony Dream Machine Digicube for bedside, alarm clock duties. 
Isn't this covered by warranty?
You have to understand,
The poor black level performance is a result of the generation TFT LCD Sony used in their Z/ZL models.
All Z/ZL models suffer from it.
That's why the current generation since the Z2 use IPS LCD instead, which provide superior black level, viewing angles, and power efficiency.
The Z/ZL are simply a reflection of Sony Mobile's best effort when they were released.
Things have changed and markedly improved since then, from the Z2 onwards.
In short, get yourselves a Z2.
It's a massive improvement on both Z/ZL in all areas.
And it's very competitively priced, now that the Z3+/Z4 is about to be superceed by the Z5 series.