color sampling

[Bill Rankin]

The HPX 170 shoots with the color sampling 4:4:2. IF you downconvert that video clip to SD is there any loss or change to that color sampling?

This might be a simple, common sense question, but I do not fully understand the color sampling concept.

[TingSern Wong]

For normal DV (baseline), on NTSC, the standard used is 4:1:1. PAL will be 4:2:0. You don't have to use those if you shoot DVCPRO50 on your HPX170. DVCPRO50 is the best codec for SD - and it uses 4:2:2 as well. So, if you set your HPX170 to use DVCPRO50, you will get 4:2:2 all the way.

I think you got your info wrong - HPX170 don't shoot in 4:4:2 - No "cheap" camera shoots at 4:4:2. It has to be 4:2:2.

[David Heath]

Originally Posted by Bill Rankin

The HPX 170 shoots with the color sampling 4:4:2. IF you downconvert that video clip to SD is there any loss or change to that color sampling?

There are more misconceptions around the whole subject of colour sampling than almost anything else in the world of video.

Firstly, yes, you mean 4:2:2. Which determines the ratio of chrominance pixels recorded to luminance pixels, and 4:2:2 means as the same number vertically, but only half as many horizontally. So, in 720p mode, that means each luminance frame has 960x720 luminance pixels but 480x720 chrominance pixels - 1 each of U and V.

The operation of downconversion will change all that totally, and what colour space you end up in will depend on what format you record in. For NTSC, luminance will always have a frame size of 720x480, but chrominance will be either 360x480 (for 4:2:2), 360x240 (for 4:2:0), or 180x480 (for 4:1:1).

In other words, even if you downconvert to an SD 4:2:2 format, the chroma frames will still be substantially changed. Interlace makes the whole subject even more complex than it appears from that.

The sampling figures are RATIOS (of chrominance to luminance), not absolute values. And the downside to the HPX170 is that DVCProHD subsamples the luminance horizontally, from 1280 to 960 horizontally for 720 modes, and 1920 to 1280 for 1080 modes. So, for the latter, you'll only get 640 chroma samples (1280/2) horizontally compared to 1920/2=960 for a camera which records full raster, like the EX.

It doesn't end there. The subsampling figures only tell you about the recording resolution - not what the camera front end is capable of. So whilst (in 1080p mode) the HPX170 is capable of recording a high chroma resolution vertically (1080 chroma samples), the chipset isn't capable of doing that justice. (Pixel shifting only enhances luminance resolution, not chrominance, from what the chips would lead you to expect.)

There's some good theory at Chroma subsampling - Wikipedia, the free encyclopedia but bear in mind that the notation only represents a ratio. Big ratios may seem good, but if I asked you if you'd rather have a half of the money in my right pocket, or a quarter of the money in my left, what would you say? Correct answer is "what's the total in each pocket". A quarter of $100 is a lot better than a half of $50, isn't it?

[Bill Rankin]

Thanks Tingsern and David.

I am in the midst of chosing between HMC 150 and the Pana170, and I just want the better final picture and easier to edit codec. Most of my final output will be in SD for the near future.

[Barry Green]

The HPX170 has a much easier to edit codec, 4:2:2 color sampling, variable frame rates, HD-SDI output, time lapse/intervalometer functions, and a few other niceties over the HMC150. If you had the choice of the HPX170 or the HMC150, I'd say HPX170 every single time; the only real reason to consider the 150 over the 170 is the price advantage. Plus, the HPX170 does shoot in SD, whereas the HMC150 doesn't, and the HPX170's DVCPRO50 with 4:2:2 is absolutely gorgeous standard-def footage.

If you want to see fairly identical footage from each, you can download the HPX170 and HMC150 footage from The Great Chroma Key Smackdown, here:
Chroma-Key-Smackdown.zip

I put up GH1, 7D, HMC150, HPX170, and HMC40 footage all shooting the same green-screen key test, so it's all fairly similar/nearly identical footage, all in 1080p, so you can compare for yourself.

[Bill Rankin]

Thanks Barry,

[TingSern Wong]

If you want a camera that produces easy to edit video, go for HPX170. It uses P2 cards - so please factor that into the final pricing of your camera. Codec will be DVCPRO HD.

HMC150 uses AVCHD codec to write to cheap SD/SDHC cards. AVCHD is very highly compressed - and you have to transcode that to an intermediate codec first before the NLE can use the data.

[Bill Rankin]

It is my understanding that Premiere Pro (CS4) will edit AVCHD natively. I just the better picture in a given situation. Easier editing is a definitely plus though.

[TingSern Wong]

PPro (CS4) will not play back full frame AVCHD. That's the problem.

There are pros and cons of DVCPRO HD vs AVCHD. I cannot type this here - too much material.

The best advise I can have to you - borrow both cameras, shoot a 5 minutes scene on both cameras, then try editing it using the NLE of your choice, and see the final video. I am sure a dealer worth his salt will definitely loan you both cameras for 10 minutes, yes? :-).

[Christian Magnussen]

Yes some applications can edit avchd natively, but you do need a very powerful workstation if you plan to skip transcoding, laptops are not much use for editing avchd efficiently. Dvcprohd on the other hand is easy peasy compared.

If a Hpx170 fits your budget I would go with that over HMC150 any day. With hd-sdi you also have a workflow for delivering finished edits to clients, as an alternative to compressing or sending the P2 files on a drive as long as your NLE supports sending video back to P2. And the 4:2:2 if not worth it's weight in gold...is a very neat future to have. Also a P2 card is much more likely to be supported at different networks than consumer avchd, a lot of networks around the globe still require SD if you deliver directly...

[Bill Rankin]

"With hd-sdi you also have a workflow for delivering finished edits to clients,..."

I am not sure I understand what you mean by the above statement.



Edit: Nevermind...I understand.