Why does SNR stop dropping at high ISO on some Pentax cameras?
Asked 5/3/2013
2 views
2 answers
0
I noticed in DxO SNR graphs for the Pentax K-30 and K-5 that after about ISO 1600 the signal-to-noise ratio does not seem to decrease much. Up to ISO 1600 these cameras look similar to the Nikon D3200, but above that they diverge. Is there a technical explanation for this? Could the camera be applying some kind of noise reduction to the RAW data?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
3
Most likely some noise reduction is being applied to the RAW files by the camera, in a way that cannot be disabled by DXO.
Someone discovered Sony were applying this technique in at least one model by showing the Fourier transform of a RAW blackframe which clearly demonstrated the high frequencies were missing.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
13y ago
0
Generated from our catalog & community — verify before relying on it.
A likely explanation is that some noise reduction is being applied to the RAW data at higher ISO settings, in a way that cannot be fully disabled by the test workflow. If that happens, measured SNR may stop falling as expected because the camera is smoothing noise before the RAW file is written.
This kind of hidden RAW processing has been observed on some cameras before. One way it was detected was by analyzing black-frame RAW data with a Fourier transform, which showed that high-frequency detail had been removed—consistent with noise reduction.
So yes: if the Pentax results flatten out above ISO 1600 while a comparable camera continues to decline, in-camera RAW noise reduction is a plausible reason.
Recommended products
UniqueBot
AI13y ago
Your Answer
Related Questions
What does a sensor SNR rating in dB actually mean?
Why do higher ISO settings often look worse even if my measurements suggest better SNR?
How does doubling ISO and halving shutter speed affect SNR in shot-noise-limited images?
Has camera sensor signal-to-noise ratio improved since 2008?
What’s the difference between Dual Native ISO and Dual Conversion Gain?