Pentax K-5 High ISO NR
Pentax K-5 High ISO Noise Reduction
The Pentax K-5 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 80, another 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 80 gets one itself, ISO 100 and 140 share a setting, ISO 200 and 280 share one, etc.). Kudos to Pentax to providing such excellent control over noise reduction for JPEGs, though as you can see from the crops below, the "Off" setting does not disable noise reduction at higher ISOs.
See for yourself how the Pentax K-5's four noise reduction levels work under daylight-balanced lighting. Click on any of the crops below to see the corresponding full-sized image.
The above crops show the effects of the 4 levels of high ISO noise reduction, under our studio HMI lighting we use to simulate daylight. The Medium setting strikes a good balance between noise and detail, however subtle detail in the red cloth swatch starts to suffer already at ISO 800. It's interesting that at ISO 800 and 1600, the "Off" setting does leave more detail (and chroma noise), but at higher ISOs, it appears to be applying at least as much noise reduction as the "Low" setting, if not more.
How does the Pentax K-5's JPEGs compare to state-of-the-art APS-C models with similar resolution at high ISOs? See the following table which compares at the default noise reduction setting.
All four cameras in this group show similar levels of noise at ISO 800 with the Canon 60D and Sony A580 showing a touch less, but the latter are starting to blur tone-on-tone detail in the red leaf fabric. At higher ISOs, the Nikon D7000 starts to pull away from the pack in terms of low contrast detail, with the others applying stronger chroma noise reduction. However, the K-5 and 60D both do a slightly better job at keeping higher-contrast detail more clearly defined. It's also no surprise that the 18-megapxel Canon 60D outresolves the other three which all have 16-megapixel sensors. All-in-all, a very good performance from the Pentax K-5.
Here's a comparison of the K-5 with its predecessor, as well as other semi-professional models:
Here, we can see just how much better the Pentax K-5 is over its predecessor, the K-7, and the improvement over the older generation sensors and/or processing of the Canon 7D and Nikon D300S. Note that the K-5's overzealous chroma noise reduction is rendering the blue text in the scale almost as monochrome at very high ISOs.
See the High ISO RAW crops page, which is a much better indication of relative sensor performance.