Camera Labs

Background: Camcorders output a full uncompressed image with 4:2:2 chroma subsample while filming. Capturing it directly results in a dramatically better image.

The Canon 5D Mark II (and the SX1) output AVCHD at 40-45Mb/s, close to the limit of a Class 6 SDHC. The result is close to the image quality of a 100Mb/s conventional data stream.

The Canon's output the Liveview image to HDMI during capture, which is useless other than for focusing. The high bandwidth recording makes that less important.

Most AVCHD camcorders are 9-17Mb/s, reflecting the data storage available a few years ago. A few, the prosumer Panasonic HMC150 and the new high end Canon HF S10/100, record 25Mb/s.

The announcement is that the GH-1 would record at 17Mb/s. That is half or less than half of the data rate of the Canon, and IHMO insufficient to create an image better than a consumer HD camcorder. The recording rate is the limiting factor. The lens will create good picture edge sharpness (low spacial frequencies) but textures (mid spacial frequencies) will be hammered.

Did anyone find out if it is like the Canon outputing the live view image or like a camcorder, outputting a full uncompressed 4:2:2 video image?

Thanks,

David

Hi David, interesting question. I looked into something similar recently while testing a Black Magic Intensity Pro card - this is basically an HDMI capture card, and the interesting thing is using it to cpature a live stream over HDMI from a camcroder becuase, as you say, it's a higher quality stream than from a recording that's not only compressed in data rate, but also colour space. Obviously to take advantage of this, you have to have your Intensity-equipped PC or Mac within an HDMI cable's length of your camera, but that's do-able in studio environments...

Anyway!

So to achieve the maximum quality from the 5D2 - ie, an uncompressed stream or one that uses a broader colour description, you'd want to capture the output from the HDMI port while its recording or monitoring.

Sadly this may not be possible in practice. As I mentioned in my 5D2 review, the Mark II can output its Live View over HDMI in 1920x1080 pixel resolution, but if you’re recording a movie, the HDMI output will temporarily reduce in quality. So to capture the full resolution of a movie, you'll need to do it in playback, by which time it has of course been compressed. I'm not sure about the colour description used by the Canons.

In terms of comparing quality, you're right that the ~40Mbit/s rates of the Canon models is much higher than the 9-17 of the GH1 and most consumer AVCHD camcorders. How much most of us will actually notice the difference in practice though is a different matter. I'm not going to comment until I've tested the GH1 and compared the quality.

The question remains though, does the Panasonic output uncompressed HDMI from its HDMI port directly from sensor processing?

The Canon's 40-45Mb/s AVCHD seems to be good enough that it hasn't been a major issue. Maybe for green screens, but not that anyone has commented.

However, without it the GH-1 might as well be a 1/3 sensor fixed lens camera. From a video standpoint it will be second rate.

Hi David, at the bottom of the design page of my G1 review, you'll see I made a note saying the G1 doesn't oputput its Live View over HDMI - well not that I could capture anyway. It seems to be just used for playback.

As for the GH1, I can't comment until I get hold of one.

I have been trying to find out the answer to that US$64k question (a 1950s TV quiz show name).

Your preview says



Are you saying it is recorded in 3:2 pull-down? I didn't think you could do that with a GOP recording format. If it did, it would throw away 20% of the bandwidth!