Can RAW images be already somewhat cooked?

Tuesday March 10 2009

Sensor Insight
Fixed pattern noise correction | Noise reduction | Conclusion

Sensors often eliminate particular kinds of fixed pattern noise (e.g., row and column noise, hot and dead pixels). This is greatly beneficial to the image and presents essentially no drawbacks. At very high ISOs, however, some manufacturers apply a more systematic noise reduction filter to eliminate noise at pixel level. In this case, the gain is can be objectionable: there is indeed an increase of SNR in homogeneous areas, but it is not likely that this noise reduction will be as elaborate as RAW converter noise reduction on textured areas with fine details. Moreover, RAW converters will get better over time, whereas noise reduction on the sensor itself will continue to definitively eliminate some information and thus affect detail resolution.