Like the Pentax K20D the K-7 features four noise reduction settings - off, low, medium and high (on the K20D this was off, weakest, weak and strong). The default setting is medium. High ISO Noise Reduction settings can be changed via custom function 19. By default noise reduction kicks in from ISO 1600 upwards but you change the threshold in custom function 20. The difference between Off and Low settings is fairly marginal at all ISOs and only affects chroma noise. The medium setting also contributes towards reducing luminance noise and appears to present the best compromise between noise and image detail.
Noise Filter Settings compared
Indicated ISO sensitivity is on the horizontal axis of this graph, standard
deviation of luminosity on the vertical axis.
High ISO Noise Reduction Crops
Noise reduction and fine detail
The biggest issue with noise reduction - especially luminance noise reduction - is that in the process of blurring away the noise it can also have a very destructive effect on the detail in an image, particularly the fine, low contrast detail you might find in hair, fur or grass. To better judge the effect on fine detail lost due to noise reduction we have shot our lovely model and produced crops from the feathers in the image. We have left out the 'Low' noise reduction setting as it only appears to apply chroma noise reduction which tends to have little impact on detail (fine contrast).
To check the effect of noise and noise reduction on low contrast detail we shoot our lovely model framed as shown here, with the new added feature of feathers. The very fine detail in the feathers will help to better judge the effect of noise reduction on fine detail.
Raw vs in- camera JPEG noise reduction low contrast detail comparison
As you can see from the crops below even at the 'Off' setting the camera still applies some noise reduction, there is visibly more chroma noise in the RAW shots. The 'High' setting is very strong and blurs most detail away pretty much from ISO 1600 onwards. Of course at higher sensitivities it's always going to be a compromise between detail and noise but when you are shooting RAW you can mix the noise reduction recipe that is most suited to your requirements.