Start scratching your head.

Sony and Panasonic side by side shooting same subject.


Sony records 1440x1080 luminance, and R-Y/B-Y is subsampled to 480x1080, at 8 bits.
Panasonic records 960 x 720 luminance, the R-Y/B-Y is sub sampled to 480 x 720, both at 8 bits. then compressed 4.3 to one
Therefore Sony records more colour information of that scene than Varicam. Sony 480x1080, Varicam 480 x720 then compressed 6.1 to one.

Leaving the final compression to the side, whatever the asethics of the pictures the accuracy of the statement that a 720p camera at 4:2:2 records more colour information than a 1920x1080 camera at 3:1:1 simply isn't true?

When we talk of colour information we are refering to recorded pixels... right?



Mike Brennan




Mike Brennan

f900 owner (but fed up with the hype from both manufacturers!)

Michael! I know how to settle this discussion now. We'll just call it even, and I'll quote Peter Gray's excellent discussion of the matter:

Riddle#2: Does the Varicam have more Color Space than the F900? Is the Varicam better for green and blue screen matting?
What I'm discovering is a bit of an eye opener in terms of Color Space and Image Sampling between the Sony CineAlta and the Panasonic Varicam.

Have you heard the common misconception, prevalent across the industry, that the Varicam records a 4:2:2 color space to tape? The argument goes like this ...... while the Varicam has less resolution in luma, it has more resolution in chroma compared to the Sony F900 CineAlta. So this means the colors are sharper, therefore the over all image will tend to look relatively sharper as well, despite there being less pixels in total compared to the F900. Consequently, this helps the Varicam produce an image that looks just as sharp as the F900. While the images are indeed amazingly similar, this reasoning is bogus.

And if this were true, then the Varicam might turn out to be the better tool for doing green and blue screen work. On the face of things, it might seem the Varicam will do a better job with pulling mattes with double the color resolution. After all you are keying to a color, and if the colors are sharper, then it should work better - right? Again, this reasoning is bogus. The real story is a little more involved, as I will try to explain.

It is amazing how entrenched the misconception is that the Varicam has approximately double the color space of the F900. But in a sense this is true ..... it all depends on how you look at it! Lets start by looking at precisely how each HD camcorder system processes and records its images to tape. But in so doing, we can't lose sight of the fact that the starting point for each camcorder is different. The Sony CineAlta has approximately twice the number of pixels per CCD compared to the Panasonic Varicam (2.2 megapixels for the F900 verses 1 million pixels for the Varicam).

The first step in both cases is pre-filtering in luminance. Both systems use the same reduction factor, namely 1.33*. The F900 starts with 1920 pixels per line, and filters down to 1440 in luminance (1920 divided by 1.33 = 1440). The Varicam starts with 1280 pixels per line, and filters down to 960 in luminance (1280 divided by 1.33 = 960). The original "1920", and the original "1280", are defined by their respective format specifications.

Next, chrominance is sampled at 3:1:1 in the case of the Sony camcorder, and at 4:2:2 in the case of the Varicam camcorder. So the CineAlta has 1440 in luminance and (1440/3)= 480 in chrominance, while the Varicam has 960 in luminance and (960/2) = 480 in chrominance. Note that both systems now have precisely the same number of pixels per line, namely 480, representing color information!!!

While both systems have equal chrominance resolution, the Sony HDCAM has 50% more luminance resolution. This is not surprising considering it started out with twice the number of pixels in the first place.

Another way to look at this is as follows:
HDCAM = 1440 in luminance, and (1440 /3) = 480 in chrominance = 1440:480:480 = 3:1:1
HD Varicam = 960 in luminance, and (960 /2) = 480 in chrominance = 960:480:480 = 4:2:2

In an absolute sense, the CineAlta and the Varicam have identical color space i.e. 480 pixels per line!!!

But relatively speaking, the Varicam samples a slightly lower resolution image at a slightly higher rate for its colors. "A-little-more-of-a-little-less" means there is no net gain in terms of color space compared to the CineAlta. However, the CineAlta has a comparative advantage in terms of resolution in luma (or the black and white component of the image) by a factor of a half i.e. 50% more resolution in luma. Or 1440 pixels compared to 960 pixels (mathematically speaking: 960 x 50% = 480, then 480 + 960 = 1440) (or 960 x 150% = 1440) (or 1440/150% = 960) etc.

Sony's 3:1:1 exactly equals Panasonic's 4:2:2 in terms of color space in an absolute sense. But in respect to the Varicam's own inherent line resolution, it has twice the rate of color sampling compared to the CineAlta. This leads to the conundrum that it is true to say the CineAlta and the Varicam have identical color space, but at the same time, it is also true to say the Varicam has twice the color space of the CineAlta. This is of course is contradictory.

The truth of the matter can only be resolved when you look at the total number of pixels per line that are sampled for color information.

3:1:1 color sampling of 50% more line resolution = 4:2:2 color sampling of 50% less line resolution (QED).

To complete the story, both camcorders sample at 10 bit, pre-filter, compress, and record to tape at 8 bit. In other words, both systems work in a very similar way, and indeed, they both produce very similar looking images.

Many people believe that the Varicam performs better for green and blue screen matting processes, compared to the Sony F900. I think the reality is that they are about the same in their blue and green-screen matting abilities, as the discussion and the associated numbers above indicate.

I say we should just call it quits and basically shoot a nasty look over at the engineers at Sony and Panasonic for creating these big resolution lies and misconceptions. How dare they call the CineAlta a 1920x1080p24 camera? And how dare they call the VariCam a 1280x720p camera? I love how Peter just basically concludes that it's all the same, and that it really doesn't matter that much after all. I tend to agree.

I still love mine, though... And in some way I'm more interested in discovering the ultra slow motion stuff you got me looking at. I'm seriously considering one of those Itronx or AOS cameras...

--rune

Mike,

I think what he means is that it's all very relative, and everybody is kind of twisting and turning things when it comes to the specs of the cameras. I also think that in reality where we see a difference is in how the cameras are set up and what glass you put in front of it and how talented the DP is and how well the material is color corrected, and eventually how well the 35mm projector is set up. The tool is but a tool in the hands of a great artist.

As for getting a 4;4;4 camera, I don't think I'm going to bother for a long while still. I think true movie makers will head towards cameras like the new digital Arri with some exotic storage medium, with a 35mm sized imager, and 2/3" HDCam SR will be judged "expensive but like not really good enough to compete with those types of cameras" and my VariCam (and your F900) will still be high enough end for certain budget projects that it won't matter. I might consider some form of uncompressed storage, though, depending on how that comes out. CineRAM is way too expensive, but the quality coming out of the HD-SDI port is so much higher than the compressed DVCProHD that I think this is where I will try to extract as much juice from the camera as possible...

Right now we're shooting with two VariCams on a big, albeit rather flawed feature film down here, and while the acting and directing might suck a bit, the image quality is wonderful, and I can't wait to see the whole thing on 35mm later this spring. So far everything we've put on 35mm has looked every bit as good as the other stuff being projected, so I totally stopped worrying about that.

--rune

So which camera?...The one the client demands!

Who said producers understand making sense. I'm thinking of the various networks and cable companies that are demanding the Sony F900. Or NBA that insists on panasonic. You're not going to get a chance to convince them otherwise. If you own the wrong camera...tough.