S-Log or Cinegamma?

[alisterchapman]

The new Sony PMW-F3 can record using normal standard gammas and hypergammas, which compress highlights and increase the dynamic range to 460% and S-Log which is, as it’s name suggests an “S” shaped logarithmic gamma curve that compresses both highlights and lowlights giving upto 800% dynamic range. However the noise figures given by Sony are very different for S-Log and Hypergammas.

It will be interesting to see what the ramifications of the F3?s, 63db noise figure using standard gammas and hypergammas, vs the 57db nf using S-Log.

S-Log on the F3 will give you almost an extra stop of dynamic range but doubles the amount of noise. In most grading situations noise is the defining factor as to how far you can push the image in post. With normal gammas, at 57db the noise level is at the point where 10 bit recording brings little advantage as the noise is still around the minimum sample size. But S-Log is different as the distribution of data across the gamma curve is not linear, you must have 10bit recording for S-Log to work correctly. With the standard gammas at 63db there will be a definite advantage to recording 10bit.



The noise behaviour suggests that the true zero point noise level for the F3 is 57db, but that for “normal” use, due to the sensors very large dynamic range I suspect that Sony have chosen to reduced the gain by 6db, thus reducing both the noise and dynamic range. In effect the camera is operating with -6db gain switched in as default. However the sensor is sensitive enough to still give excellent low light performance despite the reduced gain and has more than enough dynamic range to still give the 11 stops that can be recorded with Hypergammas. This points to excellent low light performance as with +6db of gain switched in (with standard or hypergammas) your still going to have a 57db noise figure and at +9db gain it should have about the same amount of noise as an EX1 at 0db! Ah.. the delight of big pixels.