Split Compression

[Evan Owen]

As long as the compositor knows where the line is I don't see any problem - one already deals with spill suppression, holdout mattes, garbage mattes... a simple geometric mask shouldn't be too hard, but as I said, it means the compositor needs to know exactly where that line is.

Except that it's not just a simple line. Which side of the line was compressed more differs from shot to shot, and there are often other definite edges showing differing levels of compression throughout the frame. Manny's shots, especially girl_02.png, show it pretty clearly.

 

[Rob Powell]

As long as the compositor knows where the line is I don't see any problem - one already deals with spill suppression, holdout mattes, garbage mattes... a simple geometric mask shouldn't be too hard, but as I said, it means the compositor needs to know exactly where that line is.

You're right, but IMO it's tough enuf to deal with the "normal" challenges of compositing, without having a known issue that effects every frame and requires an addtional matte or adjustment.

 

[Rob Lohman]

Not in the strict sense of the term, no. But all the shots I've seen show lots of resolution in the green channel, which doesn't seem to have any compression artifacts (visible anyway), while the red and blue channels exhibit significant compression artifacts and loss of detail.

At 4K, it doesn't seem to affect the image quality as much as 4:2:2 would normally, but you have to admit, there's not exactly an equal level of resolution among all three channels.

Of course, bayer has two green channels and "only" one red & green. Since that is an important fact in a debayer algorithm you focus on that, obviously.

4:2:2 implies you actually drop full samples while they were available. After 4:2:2 there is still compression happening in those systems. We have the compression step, but don't drop samples before it.

 

[Evan Owen]

Of course, bayer has two green channels and "only" one red & green. Since that is an important fact in a debayer algorithm you focus on that, obviously.

4:2:2 implies you actually drop full samples while they were available. After 4:2:2 there is still compression happening in those systems. We have the compression step, but don't drop samples before it.

Right.

One thing I've been wondering. If the compression takes place on the pre-demosaiced RAW data, why is the green channel so pristine compared to the other two? Yes, I know there are twice as many green photosites, but that would mean the red and blue channels would show only about twice the compression. It looks to me like the green channel hasn't been compressed at all compared to the other two.

This whole 'compressing RAW' thing gets confusing to me sometimes. :blink:

 

[erbp]

I am interested in the science of what's happening, but mainly I would appreciate an answer about the artifacts along the line of "this is the best (or nearly) that can be done given the bandwidth of Compact Flash" or "we think we can get the blue channel as pristine as the green".

Also, I understand that we are talking about something that an audience watching on any modern presentation (less than 4k) isn't going to notice. However, it is affecting overall quality. I would not have even thought to look at the different channels if there wasn't a noise problem apparent in the RGB picture.

 

[Evan Owen]

...
I would not have even thought to look at the different channels if there wasn't a noise problem apparent in the RGB picture.

I wouldn't exactly call it a 'noise problem'. RED's sensor has the lowest noise of any digital sensor I've ever seen... :usd:

I'm talking about this stuff alot because I'm interested in the science behind it, not because I don't like the image and feel a need to complain about it... but yes, it'd be nice to know if (like I suspect) these things will be improving in the future.

 

[Stuart English]

Compression

Compression

Guys, we absolutely appreciate the interest in this subject. But its also only fair to say the precise details of what we are doing is RED team internal information only. So forgive us if we don't answer your specific points.

The most important information is: we are never satisfied, and will always look for ways to improve.

 

[erbp]

I wouldn't exactly call it a 'noise problem'. RED's sensor has the lowest noise of any digital sensor I've ever seen... :usd:

I'm talking about this stuff alot because I'm interested in the science behind it, not because I don't like the image and feel a need to complain about it... but yes, it'd be nice to know if (like I suspect) these things will be improving in the future.

I didn't mean anything I said as a complaint. And you're right, maybe "noise problem" isn't the right phrase. Here's where I'm coming from: I didn't reserve a Red to replace an HVX or any other digital sensor. I did it because I'm interested in replacing the workflow and reliance on labs that goes with 35mm. Right now, in my opinion 35mm beats Red as far as latitude and resolution but just barely. I would still choose Red because of the workflow, but I sure would feel better if I didn't feel like I was trading quality for ease of use. And if this compression can be improved that eliminates 35mm so I don't have to even think about it.

 

[jbeale]

Right now, in my opinion 35mm beats Red as far as latitude and resolution but just barely.

Have you done a controlled test (Red & 35mm side-by-side, shooting same scene at the same time with the same lenses)? With what film stock? I would be very interested to hear the detailed observations of anyone who had done this.

 

[erbp]

Have you done a controlled test (Red & 35mm side-by-side, shooting same scene at the same time with the same lenses)? With what film stock? I would be very interested to hear the detailed observations of anyone who had done this.

No, I haven't done a test. I don't get my Red until December. I would also like to see a side-by-side.

It's just an opinion based on feature work with Kodak 5217 and 5201 and scouring the forum for every image that's posted. I'd love to have access to RedAlert to see the latitude for myself.

 

[conrad gaunt]

We don't do 4:2:2

No, but people post jpegs images on the forum, which might make images look worse than they are? Trying to help you out here...

 

[Häakon]

Have you done a controlled test (Red & 35mm side-by-side, shooting same scene at the same time with the same lenses)? With what film stock? I would be very interested to hear the detailed observations of anyone who had done this.

I have, and I will be posting observations soon. I'm actually in talks with a fellow RED User who has been kind enough to offer his suite so we can all look at the footage on a 2K projector next to a 35mm projector at the same time. I've already done enough examining on this footage to know which I believe will look better, but I would like to see them projected simultaneously to really see for sure.

Film may still have a slight edge in the latitude department, but I'm not convinced it holds more resolution. At least not 35mm. I think if you saw them both projected in their full size you would be pretty blown away.

 

[Gavin Greenwalt]

Although I have to say on the other side of the coin--having just watched cloverfield: 720p looked fine by my eyes.

If you're going to a film print, I think George Lucas might be right: 1080p is more than enough.