Pixelization, compression artifacts and noise

[Emanuel]

A) What's the worst: pixelization, compression artifacts or noise?

B) And real danger?

C) What are the real possibilities in order to correct any of all these problems in post production?

Specially, considering the Yuval's report (LINK (http://www.dvxuser.com/V3/showpost.php?p=373311&postcount=18) for his first report's post) about pixelization and compression artifacts regarding the HVX 35mm film-out screening:
«(...)There were compression artifacts in mid-tones, (especially in scenes that were shut in low-light conditions and under exposed and then were brightened in post).
The image was quite sharp and I couldn't notice any pixilation (which was very impressive), and it surely looked very filmic indeed! :) (...) It seems to me that one practical lesson from this screening would be to be careful when shooting not to under-expose the image, because brightening the image up in post will increase compression artifacts to an unacceptable level».

BTW: Because I'm not a techie, as well, several video glossaries don't say the same and, above all, following the excellent report of Yuval: I make here, for this purpose, a distinction between «pixelization» as that mosaic distortion that any one can say that it's an electronic medium technology (more common in interlaced than progressive) and «compression artifacts» to the undesirable elements as visible corruption of the image from a compression codec. Finally, for «noise», we consider the grain level that we can find in any image, from an electronic device or not. It can have influence in terms of copies generation (mostly in reason of DA -> AD, that is, where there is an analogue process) but mainly as opposite of (the quality of) sharpness.

Note: Besides the pool - in order to know the first concern of the majority - it's more important and interesting IMHO to listen the experts, as well, all of us that want discuss it and share to all community any important point concerning the subject.

[surf]

all

it depends on your display format. ie in cinema or at home on TV or on computer.

[Emanuel]

As a serious concern?...definitely not on computer! :)

[phd]

I always use a projektor and 250 cm screen(100"). TV and PC have to small screen

[Yuval Shrem]

Hi,

I see my brief report was mentioned here, so I'll just clarify a few issues.

1) There was no visible pixelization at all. That is in spite the fact that the footage screened there was only 720p (and not 1080)

1a) the video noise was visible in blue areas, but in very acceptable levels (Looks a little bit like film grain). This noisy blue channel is typical to video cameras in general, and not just the HVX200m and it has to do with how CCD technology works.

2b) Artifacts were apparent in mid-tones, especially in low contrast situations, and especially in scenes which were under exposed and then were pushed (amplified / brightened) in post.

2) The only serious issue to my eyes, was the issue of compression artifacts in mid-tones. (I should mention though, that there were no visible compression artifacts in dark areas, bright areas and high contrast scenes.)

3) In order to prevent these problems I would recommend making sure to properly expose scenes, and maybe I should also say supplying the camera with more information by giving it more light while shooting (and I don't mean much more light, just a little bit more...) so that you wouldn't need to change video levels and brightness in post. This is almost sure to prevent those problems. most of these problems would have occurred if these scenes were shot on film with the same exact lighting setup, only instead of compression artifacts, you would have gotten annoying film grain with washed-out image. I mean, when you plan to go to the big screen, you can't get away with not lighting scenes for a proper exposure, and then change it in post (at leased not when you're using a compressed video format).

As I mentioned in my post about that first screening, there were a few issues that might have affected our impressions, such as the relatively grainy film-stock used for the transfer, an HD-CAM re-compression, and an unnecessary boost of the blue channel in the film-out transfer. It will be much safer to base any serious conclusion on a later film-out test, which will be done of native DVC-PRO HD and with a different film-out process (different color-timing and different film-stock), so please take anything I said about that test-screening as first impressions only, and not as a final conclusion.

I hope that helps,

Yuval.

[Emanuel]

It helps!

Thanks a lot, Yuval!

For me, your report is the most important one - of the year - but for sure, it's not a final conclusion. Just a wise progress report.

Grateful,
Emanuel