After growing tired of lugging my big and bulky DSLR camera around everywhere I began looking into smaller alternatives and picked up a Panasonic DMC-G6. A relatively cheap mirror-less MFT camera. The GH2/GH3/GH4 series cameras from Panasonic have proven to be quite successful both for photo and video so I figured the G6 might be a good and cheap starting model to get to know the Panasonic world a bit. The G6 is similar to the GH4 with regards to handling and menus etc. After using it for over six months I must say that I'm quite pleased. It's performing very well an has a lot of features I would rather expect to see in a higher-end camera. It comes at a somewhat buggy price though but the only really serious bug I've encountered so far is in the "Pixel Refresh" feature. It annoyed me for a long time but now I may finally have found a solution.

Image sensors and pixels

Every CMOS and CCD image sensor today have random faults. Even the high-end ones. All pixels are not equally sensitive and some may even be completely dead and locked at a full black or full white level. Every sensor manufacturer has a threshold on how many errors are acceptable in production. Sensors that does not reach this threshold are trashed and it is safe to assume that no sensor have 100% working pixels. Especially over time since age and radiation will create more defects. The most devestating defect is when pixels are too bright. They are easily spotted by the human eye. This is what is commonly referred to as hot pixels or stars. Camera manufacturers use software algorithms to calibrate each sensor individually to compensate for pixel defects. Some camera models require a service technician and/or special tools to perform this calibration and some models can perform the calibration in-camera, either initiated by the user or automatically.

Discovering the Pixel Refresh function

Panasonic have decided not to hide the sensor calibration feature from the user and they call it "Pixel Refresh". The details around this function is very vague and the manual is not very helpful. The manual does however say the following: "Imaging device and image processing is optimised when the camera is purchased. Use this function when bright spots that do not exist in the subject get recorded." Okay, Pixel Refresh is clearly meant to hide hot pixels. That's great! Eventually a few bright pixels showed up on my video footage and I decided it was time to try out the Pixel Refresh feature and YIKES! After this all my pictures and videos looked like the milky way! I immediately realized that something must have gone very very wrong. There were several extremely bright pixels clearly visible even at ISO 200. What was even more baffling was that the hot pixels moved around when changing the sensitivity/ISO and some pixels were only visible on the LCD/WF and some were only visible on the recorded media. Running Pixel Refresh again did not really improve the situation but after countless other attempts I really began to suspect that this had to be a software error. Spending a several hours factory resetting, updating firmware (to v1.2) and speaking to Panasonic tech support did not help either. Eventually Panasonic called for a warranty repair and after a few weeks I got my camera back with a new sensor and even more hot pixels. The service center clearly did not get the situation at all...

My solution

Almost ready to give up on the G6 I started to methodically execute the Pixel Refresh function after placing the camera in different operating modes and settings. I eventually found a combination that actually worked! The most important lesson learned here is that camera settings severely effects the Pixel Refresh function. In general, when executed, the function will display a progress bar. If this progress bar does not progress smoothly and ends with a big jump to 100% it means that the process has failed in one way or another. It took a lot of trial but here is my procedure for running Pixel Refresh on the G6 that actually provides usable results. - Let the camera reach operating temperature - Enter manual photo mode "M" (not manual video mode!!) - Turn electronic shutter ON - Set ISO to 1600 - Put lens cap on (keep stray light away from the sensor) After performing the steps above run Pixel Refresh. The process may need to be repeated in order to get rid of all hot pixels. The procedure above has worked several times now on my G6. I can not tell if it will be the same for other G6's or other Panasonic cameras but it would be interesting to know.