the whole 4:2:2 thing - to David Heath

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Bounce

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Hi all. I've been on this forum before but lost my user name and email a long time ago. Big time reader tho.

Okay.




"
David Heath
August 31st, 2008, 09:12 AM

So your point is that the 4:2:2 output might not have much of an impact on the final product compared to the 4:2:0 using the Panasonic cameras?

Do you think keying work would be improved?
"Yes" to the first question above, and "depends" to the second.

Think of "4:2:2" and "4:2:0" recording modes as containers, capable of "holding" resolution (!) Let's say they're each capable of holding 1 litre of luminance resolution :), when 4:2:2 will then hold 1 litre of vertical chrominance information and 0.5 litre of horizontal chrominance information. For 4:2:0 both the chrominance figures are 0.5 litres.

The approach you're suggesting (record HD-SDI via an XDR) effectively replaces a 0.5l container with a 1l container. What I'm saying is that you'll only get an improvement IF the camera head is capable of producing more than 0.5l of vertical chrominance information in the first place. For a camera like the EX the answer is obviously "yes" - it's chips have 1080 pixels vertically each of r, g and b. But for a camera with 960x540 chips, the answers no. Pixel shifting techniques may get about 0.6-0.7l of vertical luminance information (up from the 0.5l you'd expect without pixel shift), but they can't do anything for the chrominance information. You're stuck with 0.5l - double the size of the container, and you just end up with it half empty!

As regards the question of whether keying work will be improved, my guess would be that an XDR type device may have lower overall compression, which could only be a good thing, but the effect of the 4:2:2 recording would be small in this case.

As far as the HPX500 goes, on the up side it's 2/3" chips, and they have proper optical low pass filters to help counter aliasing. (All 1/3" cameras don't, AFAIK). On the other hand, they are 0.5MP chips, so the chrominance resolution won't be as good as a 2MP camera, regardless of the colour space. Colour space numbers are ratios, not absolute numbers, and you have to pay regard to the luminance numbers to make any sense. Would you rather have 50% or 25%? Now what if I asked "50% of 2" or "25% of 8"? In that case 25% is obviously better than 50%, in others 4:2:0 can be better than 4:2:2 by similar logic - you have to make sure like is being compared with like.

I'm afraid that at the end of the day you get what you pay for."





Thus if the 170 has the same chip then converting the 150 MPEG4 file to the DVCAM HD 4:2:2 file (or the cineform 444 for that matter) will it result in the same amount of colour information? Save for the compression degradation?

Thanks
 
Bounce said:
Thus if the 170 has the same chip then converting the 150 MPEG4 file to the DVCAM HD 4:2:2 file (or the cineform 444 for that matter) will it result in the same amount of colour information? Save for the compression degradation
Click to expand...

What a coincidence... I wrote a post on this in another thread yesterday... An interesting conclusion is that the DVCPRO HD codec's 4:2:2 chroma is an overkill for HPX170 - lot of the chroma information being carried by the codec is redundant, because of the limited chip resolution. This not a big problem considering enormous 100Mbit/s DVCPRO HD throughput. But... Things get worse when shooting 720p - DVCPRO HD bitrate becomes 40Mbit/s then. No surprise HMC150 with its increased raster size, 4:2:0 chroma (better bitrate usage) and advanced MPEG4 compression outperforms HPX170 in 720p.
 
Not realy buying this 150 out performing the 170 thing. There is clearly a difference in overall color rendition from both cams. IF someone can post a 720 heavy color corrected still of both cams i'd love to see.

I would not even say the 150 out performs the a1 when factoring the a1s native resolution and glass quality, and especialy after you have dialed in one of stevens presets.
 
reem12 said:
Not realy buying this 150 out performing the 170 thing. There is clearly a difference in overall color rendition from both cams. IF someone can post a 720 heavy color corrected still of both cams i'd love to see.
Click to expand...

Didn't have the chance to compare them side-by-side, but I can't think of any reason why there's a difference in color rendition. I don't mean there isn't any. I'm just trying to find out why - everything, but codec, is the same in both cameras - glass, sensors, processing chip. Both AVCHD and DVCPRO HD are 8-bit color... The only difference seems to be the chroma downsampling factor, but, as I said, 4:2:2 is an overkill for these cameras (my opinion). Maybe there's something in the encoding algorithm itself that ruins the color information - that would be very strange, though.
Or... Panasonic does something (on purpose) to make the HMC150 footage look worse ;)

I realize cc can reveal differences in more apparent way. But I don't really think comparing heavily cc-ed footage is the right procedure unless the original codec (prior to cc) is the same. Probably the most fair way would be transcoding the footage from 170 and 150 to uncompressed, then applying cc.Wish I had both cams at home ;)
 
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no answer?

i'l recap: if the 150/170 produces colour (chrominance) information that can not fill the 4:2:2 codec - therefore only 4:2:0 is necessary.

THUS the only reason for the 4:2:2 DVCPRO HD codec is its lighter compression ratio (less artifacting and possibly a touch more detail).

As Trez alluded to, the best test would be to transcode the footage from both cameras to the Cineform 4:4:4 codec and see what colour control you have. A further test would be to transcode only the 150's footage into DVCPRO HD and see how much you lose compared to the 170's native DVCPRO HD.

Theoretical excersise? Maybe. But it will prove that maybe the DVCPRO HD codec is only good for it's compression ratio and not its colour space (in this case only of course). Plus, I might just buy the 150 instead of the 170 and lose a bit on the compression (no biggie).

I'm no expert, i'm just talking. If someone really knows the answer to this it would be great to know.

Cheers
 
I don't see how HMC150 footage could be the same as HPX170 footage if you converted them both to the same codec -- they have the same optics, and even if there weren't "enough" color to fill 4:2:2, the HMC150 still throws out twice as much of the color which IS there as the 170 does. It IS a ratio, and if you're comparing apples-to-apples signals between footage coded to 4:2:0 and to 4:2:2, 4:2:2 has twice the color info. That Heath thing looks to me like someone rationalizing why, in theory, the EX1 should still be better at color than the 200 or 170 even though it's 4:2:0 and not 4:2:2.

If you want to see the color difference between the 150 and the 170, just try pulling keys from both.
 
so the 150 removes half the colour that the 170 does?

do you mean the chips produce the same amount of colour information, but the 150 keeps only 50 % of that?

OR are you saying that the DVCPRO HD codec simply doubles whatever is there (using its own algorithm)?
 
When you take the same signal and encode it as 1) AVCHD and 2) DVCPRO HD, the DVCPRO HD retains twice as much color resolution (and accuracy, as the article points out). To say nothing of the level of compression.
 
So it RETAINS (does not create...) twice the amount of colour information.

Cool. Thanks for answering that, as the article you mention does not mention the 150 or the 170 in its discussion of colour space and pixels (though we all know about their codecs).
 
We've been down this path before. If we stipulate to the HVX/HPX recording in DVCProHD, then we have a 1280x1080 signal laid down.

4:2:2 extracted from that 1280x1080 signal is VERY close to 4:2:0 extracted from a full raster 1920x1080. The 4:2:2 signal maintains an edge, but only slightly.

But the whole issue is pointless. If you REALLY need the color info, just come off the SDI port and call it a day.
 
SDI or HDMI? I'm confused.

So, David Heath is clearly wrong in saying that.....

"The approach you're suggesting (record HD-SDI via an XDR) effectively replaces a 0.5l container with a 1l container. What I'm saying is that you'll only get an improvement IF the camera head is capable of producing more than 0.5l of vertical chrominance information in the first place. For a camera like the EX the answer is obviously "yes" - it's chips have 1080 pixels vertically each of r, g and b. But for a camera with 960x540 chips, the answers no. Pixel shifting techniques may get about 0.6-0.7l of vertical luminance information (up from the 0.5l you'd expect without pixel shift), but they can't do anything for the chrominance information. You're stuck with 0.5l - double the size of the container, and you just end up with it half empty!"


I still want a 150 - pity it doesn't have auto audio gain......
 
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