Hi, I came across this article reg. the Canon C500 and it's 10-bit RAW capabilites.
Not sure if this was relevant under this thread or under discussion of ETTR, but I found it interesting (and I am sure most you already know this).
http://nofilmschool.com/2012/11/canon-c500-shipping-raw-4k/
"Adding gain adjustments at the sensor level produces a consistent stop range above and below the middle grey level, even at high ISOs, and reduces the overall noise in the image."
As I understand this; Canon's RAW format is special in the sense that the C500 add gain at sensor level before outputting the RAW stream, is this in a way, approaching a little more to ETTR? (to improve DR and SNR)
Q1: Could this "approach" be possible to do also with the RAW module from ML ? (if you hopefully succeed with 10bit RAW!)
BTW! I have no chance to follow the technical discussion in this thread, but:
Q2: Do you at this point have any estimates of what the DNG file size could be eg. @1920x1080, should you succeed with 10bit RAW?
(I am just curious to where 10bit might take us in case of fps/resolution)
I wouldn't say Canon does this at the sensor Level, but at the Digic after digitization. There, they use the full 14bit depth to make calculations that a raw converter would have to do, which is problematic on 10bit data. They fight the problems described below
...., yes with 10bits raw bayer we need very careful rounding and even with careful rounding 10bits depth can be inadequate. While with RGB 10bits can be (and are) OK with raw Bayer "master" there is the need to apply some heavy manipulations not needed for the ready to use RGB file. Demosaic, WB (which is a 1+ stop digital amplification for the weak channel), Color transformation from Bayer R-G1-B-G2 TO RGB (once again about 1 stop amp for the weak channel)
But with a lookup table we can have untouched the low values (keep the sampling at the same density as the 14bit starting data) where the problem is significant and gamma encode the rest.
Canon say that:
- They have "baked" in raw the ISO.
Well, in photo mode, Canon 5DIII has the ISO fully "baked" in raw for analog ISO settings (100, 200 ... 12800, no gaps in raw histograms) and partially for intermediate and expanded ISOs where its mixed analog-digiral (we can see gaps in the raw histograms).
So do Sony (and others with Sony sensors) but it happens that they stop analog ISOs lower (1600 is usual).
BlackMagic uses only the base analog gain and every ISO higher than the basic is just a metadata flag (look for "Baseline exposure" in Exif)
Canon 1Dx uses analog ISO up to 51200 and for intermediate ISOs also. All raw histograms are without gaps so either it is analog ISO up to 51200 or the DAC digitize at 16bits and after 16to14bit conversion the histogram looks full (If I had to I'd put a bet on the second). Maybe C500 goes up to same analog ISO also.
- They apply WB on the full bitdepth (14 or 16bit) raw data and then downconvert to 10bit. They gain accuracy this way and better tonality over all the range.
WB is in fact multipliers at each channel. For Canon's "Daylight" the multipliers are about R=2.0 G=1.0 B=1.5. The first thing a raw converter will do is apply these multipliers so the R & B channels will loose sampling density accordingly.
We could also "bake" a midway WB (say temp.4500K) in the proposed LUT but then we would need one LUT for each color and (if separate LUTs was possible) in the end any known raw converter would get crazy with WB/color transformations ... until someone decides to support the "crazy" ML-DNGs ..
- They use a log LUT on the 10bit output. This means they keep dense sampling where it counts (at the darks) and the sampling density decreases logarithmically as we go upright to the highlights. This way they can fit a 13-14 stop DR in 10bit log file.
It is the same we will do with the proposed 14 to 10bit LUT .. wish it is fast enough with the available resources ...
