A big new firmware update for European HTC One M9 owners has started rolling out.

HTC's flagship One M9 has received its second major firmware update today, bringing the phone up to 1.40.401.5 in Europe. The over-the-air update aims to address some longstanding issues with the device, with improvements to the camera, battery life and tweaks to the way the phone charges.

Camera optimizations are a big focus of the latest M9 firmware update.

Today's M9 update brings three major camera tweaks, according to the manufacturer. First, improved auto-exposure so images look less washed-out in brighter conditions. Second, changes to image processing in low light to reduce noise and blur, for greater clarity and improved detail. And finally, HTC has worked to reduce green and yellow hue effects in "extreme lighting conditions," so colors should appear more realistic.

The update also aims to reduce power consumption by Facebook and YouTube, while also tweaking the phone's quick charging capabilities to reduce heat output while charging.

The new firmware has begun rolling out to some European countries including the UK this morning. As always, other territories and carrier-branded versions may need to wait a little longer. Today's update is already rolling out to M9s in HTC's home country of Taiwan, and U.S. devices should get the update within the next month. The update doesn't introduce a new version number, with the phone still running Android 5.0.2.

The M9's camera in particular has been roundly criticized in the weeks since the phone's launch, so it'll be interesting to see what kind of difference these latest software optimizations can make. If you're seeing new firmware on your HTC One M9 in Europe this morning, hit the comments and let us know how you're getting on.