It is said that M4/3 cameras (E-P1, E-P2, GF1) share the same Panasonic sensor technology, but analysing some RAW files from the E-P2 and the GF1 a participant has posted on other forum (find the download link
here) I find some differences. They could just be called
fine tuning or
last minute parameters, but at least worth a review.
I have analysed with DCRAW (not yet fully supporting those cameras, but can extract RAW data from their RAW files) 2 RAW files shot at ISO800 from the same scene with the same optical exposure (aperture and shutter). The differences found:
- Real ISO: with the same aperture and shutter, GF1's RAW file got 1 stop (even a bit more than 1 stop) extra exposure that that of the E-P2. This matches DxO Mark ISO measurements that say ISO X on the GF1 is aprox. one stop further in ISO for the EP-2. It seems the ISO amplifier is working at totally different gains for the same vendor ISO setting.
- Different white balance (we can see the R channel got higher relative exposure with respect to G and B in the E-P2 than in the GF1). I wonder if this could mean a different response of the sensor (different microfilters?).
- Different number of effective pixels: 4096x3084 the EP-2 vs 4018x3016 the GF1 according to DCRAW (not yet fully supporting both cameras).
- Different Bayer pattern: RGGB on EP-2 vs GBRG on GF1. Irrelevant for IQ, but means a structural difference in the sensors.
- Different black (64 vs 15) and saturation (4091 vs 3697) RAW levels.
Regarding noise, once exposure has been adjusted to match I can see the same SNR, maybe GF1 slightly better (this would make sense according to the higher ISO gain).
On the left RAW captured highlights on both cameras, centre: RAW histograms in stops (GF1's very similar to EP-2's overexposed by 1 stop), and to the right noise comparision. The greenish colour is because no white balance nor output colour profile was applied.
Regards
