If you look at the DARKFPN graphs, the 6D shows:

- Vertical FPN: stdev 0.30 with ratio 0.06

- Horizontal FPN: stdev=0.22 with ratio 0.05

- Overall stdev: 4.59 (from DARKHIST)

At ISO 100, 5D3 has:

- Vertical FPN: stdev 0.85 with ratio 0.13

- Horizontal FPN: stdev=0.21 with ratio 0.03

- Overall stdev: 6.81

These ratios are the FPN stdev divided by overall stdev, that is, how much of the total noise is FPN. I believe it's measuring the subjective effect of the FPN (that is, a low ratio, let's say below 0.05, tells the FPN gets buried into noise, and a high ratio, say above 0.1, tells the FPN is becoming obvious).

Side note: on a 4000x5000 ideal Gaussian, the estimated vertical FPN ratio is 0.015.

octave:16> G = randn(4000,5000);

octave:17> std(mean(G)) / std(G( : ))

ans = 0.015700

**Overall stdev:**From raw_diag data, 6D has around 0.57 stops of extra dynamic range at ISO 100, compared to 5D3. To compare these numbers, you need to normalize by white-black, but from the data I have, the white levels are 15331 and 15283, which does not really make a difference.

From Roger Clark, shadow noise levels at ISO 100 are 34.9 vs 29.0 electrons, so 6D is ahead 5D3 by only 0.26 stops. The extra difference in DR may be explained because 6D's ISO 100 captures 79600 electrons, compared to 68900 for 5D3. That's 0.2 stops of extra highlight detail for 6D (so 0.46 stops difference in dynamic range).

**FPN:**The FPN ratios are explaining the

first two screenshots posted by Audionut above. 5D3 has obvious vertical FPN (ratio=0.13); 6D improves it by one stop (ratio=0.6), so vertical FPN gets buried into noise. But the horizontal FPN is slightly better on 5D3 (ratio=0.03 vs 0.05).

So, considering the FPN improvement, I'd say that, in practice, out of the box, at ISO 100, the 6D is ahead of 5D3 by around one stop.

Side note: the raw_diag grayscale analysis on dual ISO images is not relevant, because it will simply average the two components. In deep shadows, the final output from dual iso only contains data from the higher ISO.

**5D3 ISO 100 reimplemented from 200** (without black/white level tweaks)

- Vertical FPN: stdev 0.71 with ratios 0.20

- Horizontal FPN: stdev=0.14 with ratio 0.04

- Overall stdev: 3.70

So, the vertical FPN is reduced only a little (0.26 stops), but the Gaussian noise is reduced a little more (0.88 stops), which makes the FPN even more obvious (the ratio gets degraded by 0.62 stops).

And this is why we need a FPN correction tool: we have almost 0.9 stops of noise improvement on 5D3, but in practice it's not very useful because of the FPN. You have already seen the effect earlier in this thread:

here on a test sample from Audionut, and

here on a downsampled dark frame.