The high resolution histogram is impressive, but with 16 bit files derived from a 12 bit raw image, there are gaps in the data. Only 1 of 16 values have data and the rest are blank, since the 16 bit image is derived from the 12 bit by multiplying the latter by 4. Raw values 1,2,3,4 .. 4095 = 16, 32, 48, 64, .. 65536. It might make sense to allow the user to adjust the bin width used to construct the histogram frequencies. With a bin width of 16, you would capture all the values, but a larger width could be used so tht the histogram would fit on the width of the screen.
mmmm you are a bit wrong, let me explain: RAW files are 12 bit as you say, so displayed on a 16-bit range (0..65535) should have 15-hole gaps between every two tones or levels.
But we are making a double mistake:
1. White balance completely disorganises this 1+15 distribution by scaling all levels by a non integer multiplier.
2. Second, and much more important: after developing, interpolated values are calculated in the true 16-bit range, i.e. 0..65535, so they completely fill all empty gaps we had before the development stage.
Find here some samples of linear histograms from TIFF files generated using DCRAW.
- Peaks correspond to non-interpolated levels (i.e. levels captured by the sensor). R, G and B peaks perfectly match due to absence of WB in this case (I wanted to compare pure camera histograms).
- Between peaks (and also in the peaks themselves) spread all the rest of interpolated levels, completely filling the gaps.
It's not until the gamma compensation when again holes will be generated in the lowest part of the histogram, making it look like a gruyere piece of cheese.
Histograms correspond to the same scene as viewed from:
- Canon 5D: completely linear 12-bit
- Leica M8: non-linear 8 bit
- DMR back: already 16-bit in origin so no peaks will be visible:[span style=\'font-size:9pt;line-height:100%\']5D[/span]
All those 3 RAW files were developed with no WB applied (-r 1 1 1 1 option in DCRAW) and hence that awful green colour.
In a normally developed RAW file, the WB scales differently each channel and this happens:
Non interpolated peaks now mismatch and again gaps between every two captured levels are filled with interpolated new levels.
That is why I always state that ETTR doesn't provide more tonal richness
, as all levels are filled in any case, but provides more tonal precission
as peaks corresponding to captured levels get closer (after the exposure correction down), and thus interpolated levels are calculated more accurately.
And this is all thanks to the 12-bit to 16-bit conversion
, and I have heard no one saying this!!! In that way, ETTR in a camera with 16-bit native RAWs like the DMR back, will improve SNR as usual, but willl not improve at all the tonal precission of the capture as all overexposed levels will agregate after the exposure correction down to the same levels they would get in a non exposed to the right shot from the begining.
It is always best to start from the whole 0..65535 range, and zoom out with the X-axis zoom option provided. Pressing that Zoom out 4 times will do what you are looking for (0..65535 -> 0..4095). Every press scales down the histogram by 2, which equals to substracting one bit of the image file resolution.