Pentax 645Z High ISO NR
Pentax 645Z High ISO Noise Reduction
Like other Pentax models, the 645Z offers an unusually flexible amount of control over noise reduction applied to its JPEGs. In addition to "Auto", you can adjust how much NR is applied ("Off", "Low", "Medium" or "High") at all ISOs, or you can select "Custom" which allows you to choose from the same four options at each ISO sensitivity setting in whole EV increments. That is, if you enable 1/3 EV ISO steps, you get one NR setting for ISO 100, 125, and 160, another for ISO 200, 250, and 320, etc. The same applies for 1/2 EV ISO steps, but with only two sensitivities sharing each setting (ie. ISO 100 and 140 share a setting, ISO 200 and 280 share one, etc.). Kudos to Pentax for continuing to provide such excellent control over noise reduction for JPEGs.
See for yourself how the Pentax 645Z's "Auto" and "Off" High ISO NR settings compare to RAW without noise reduction under daylight-balanced lighting. (Note that these RAW images have no sharpening applied, so they look softer than camera JPEGs at low ISOs.) Click on any of the crops below to see the corresponding full-sized image.
As you can see, the Pentax 645Z applies some chroma noise reduction already at its lowest sensitivity of ISO 100. Also notice the Off setting clearly does not eliminate noise processing altogether (especially in the red channel), but it does leave a bit more fine/subtle subject detail in JPEGs than Auto, when the Auto setting doesn't select Off. Still, we wish the Off setting was less aggressive with chroma noise, at is already impacts detail in our red-leaf swatch at low ISOs.
Note that Auto selects Off for ISOs 100-800, Low for 1600-6400, and Medium for ISO 12,800 and above.