CMOS S/N deteriorating with time?

[Bob Grant]

Originally Posted by Walter Brokx

Perhaps the difference is caused by difference in compression?
More compression = less info.
A good way to decrease data is a kind of 'blurring/smoothing' which makes almost similair pixels more silimair (this can be done with pixels next to each other, but also with the same pixel over time (from frame to frame). Noise is a distinct difference between pixels (both in location and over time) that 'should' be the 'same' and is caused by the physical properties of the 'lightcapturing-proces'. (Remember: celluloid has grain, which is also the result of that light-capturing-proces.)
= > bypassing compression reveals the noise that was already there but got 'compressed away'.

(If the PP got bypassed in the SDI-signal everything would look like factory-settings)

Put simply compression = low pass filter.
I think I'm also correct in saying that chroma subsampling is also compression and will also reduce noise, slightly. What the SDI signal does bypass is the mpeg-2 compression, it also has better chroma sampling.
I think the best example of the impact of compression on noise is found in the cheap AVCHD / H.264 palmcorders. Despite their very small sensor and slow lens in low light the image is pretty much noise free. It's also pretty much unwatchable due to the horrid macroblocking.

[Piotr Wozniacki]

Originally Posted by Bob Grant

Put simply compression = low pass filter.
I think I'm also correct in saying that chroma subsampling is also compression and will also reduce noise, slightly. What the SDI signal does bypass is the mpeg-2 compression, it also has better chroma sampling.
I think the best example of the impact of compression on noise is found in the cheap AVCHD / H.264 palmcorders. Despite their very small sensor and slow lens in low light the image is pretty much noise free. It's also pretty much unwatchable due to the horrid macroblocking.

While I tend to generally agree, if you care to see the last couple of posts in the "noise" thread on the nanoFlash forum it seems that CD recognizes their Long-GoP structure is not necessarily best optimized yet, resulting in the higher datarates (like 140, and particularly 180 Mbps) producing frames of severely fluctuating quality (noise content) inside any given GoP. It can easily be seen when stepping though the GoP inside an NLE - the I, P, and B frames differ considerably; much more so than with 35 or 50 Mbps. This tends to augment the perception of shimmering noise in the actual video, due to the fast fluctuation.The "sweet spot" of L-GoP nanoFlash format, 100 Mbps, seems to be the best compromise in this regard, as well.

The consensus is that for the uncompromising quality, one needs to record in I-Frame only at 220 Mbps or above.

But I guess we're getting slightly off-topic in this thread :)

Piotr

[Piotr Wozniacki]

Originally Posted by Alister Chapman

I was noticing some soft shots on my original EX1 and as others have suggested did the usual back focus etc. This made no difference. I checked the shots through the zoom range and there was definitely a discrepancy in the backfocus. No amount of back focussing would make the problem go away and my pictures were all just a little soft. However updating the firmware and the hard reset that this performs restored my backfocus to normality and my pictures were pin sharp again.

I have a very old EX1 (1200 hours) and I recently got a new EX1R, I can't see any difference in noise between the two.

Thanks Alister for chiming in.

So, back to the thread's topic:

- could you enlighten us about the Black Balance adjustment on the EX1? Is it done automatically indeed, or does it make sense to run it manually? Its very presence in the Maintenance Menu would suggest the latter - but then again, it's inactive in my EX1 (greyed-out)...

- while we're at the Maintenance Menu: when you run the Back Focus adjustment, do you repeat it for all 3 ND positions as was touted in the EX1 early days, or is a single execution enough?

Thanks,

Piotr

[Alister Chapman]

I believe the EX1 does a black balance every time you turn it on, but I cannot confirm this.