HVX Not all it seems to be - Specs released

Firstly, let me say I have seen HVX footage and it does look very nice. I haven't seen enough of it and Canon footage to say where I would rate all of the affordable HD cameras at this point, but certainly what I have seen looks nice.

However, two claims that have been made by diehards it seems are simply not true.

Firstly, pixel count of CCD's is actually 960x540 , that is less than the vertical resolution of PAL Standard definition. How the camera compensates for this is through "spatial offset" which offsets the lines of pixels to accomplish a higher resolution. Of course, this explains the HVX's low lux capability as well because larger actual area on a CCD that captures light = more low light capability. These CCD's are progressive however.

Second, a 540 CCD means 4:2:0 sampling, which means that it holds no CCD chroma advantage over Mpeg-2 HDV like was originally marketed, but the DVCPro codec does handle fast motion better due to not GOP limitation (the tradeoff being much higher bandwith usage). It does not sample at 4:2:2 at the source, but it is converted to 4:2:2 once it hits the DSP.

All of this means, that although the HVX does produce a nice picture, have 24p recording, and utilize DVCPro, it's true CCD resolution is much less than the competitors on the market, and the chroma potential that was originally thought to be head and tails above the HDV cameras out there, is in fact only marginally better natively, and in most situations, does not equate to any advantage.

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I am posting this because I think its very important to forget brand names when looking for a camera and think about what your needs are, what camera's true factual specifications are, and what the resultant image is. I think way too many people are making up their minds over what they will buy similar to the IPOD phenomenon, based on name alone. Nevermind that there are quite a few other models out there that provide equal or superior quality for less price.

Now 24p native recording is a huge deal if you are shooting cinema especially with plans for a filmmout. But in this scenario, intelligent deinterlacing of a higher pixel count CCD (especially Canon's), could result in a much higher quality output.

This is all very important when you're going to lay out $3-$15k on a camera.
 
For the record I think it's only fair to clarify a few things. I'm not a huge supporter of the HVX - I'd rather have and Andromeda DVX myself... but I think your post gives a slightly unfair impression.

The HVX is full 4:2:2 is 720p mode. In 1080p mode it is indeed compromised due to the CCD specs.

960x540 is plenty of pixels to derive a HD image from. They use a very similar technique to the one the Andromeda guys use (and the Andromeda guys are pulling out 800 horizontal and 700+ vertical lines of real resolution). JVC does not use spatial offset, Canon does in the vertical direction, and panasonic does in both the vertical and horizontal. The ability to resolve actual detail is, in theory (not taking into account f-stop, lens etc which all cameras are limited by) is roughly 1440x810 luma which is more than enough. Quite honestly, I'm surprised none of the other companies have used both vertical and horizontal.

The 1080p mode is indeed not all its cracked up to be though. Too bad really as Panasonic made a big deal about it.
 
I wasn't at all pointing fingers at anyone specifically except those that are diehard supporters of a particular brand. I've seen many times where people are planning purchases based on "its the newest release from xxxx brand, so I'm getting it", often relying on marketing stats rather than factual scientific statistics.

The argument now is that spatial offsetting or pixel shift does not offer true choma pixels in any direction, that 540 actual pixels on a CCD means that it only has 540 pixels of chroma vertically and no amount of post techniques can increase this count... its a similar argument for why simply upsampling a standard definition image, no matter how technologically advanced, can give you a higher resolution image, it can only assist whatever is actually captured. This is by definition 4:2:0. Many are arguing that not including at LEAST a 960x720 CCD fails to give true 720 chroma data.

In terms of resolution, I'm not arguing against spatial offsetting, its not a brand new technique but fairly new in manufacturer implementation. While it can nearly accomplish what it set out to do, it is not a replacement for true pixel count. In other words, a true 1280x720p CCD in 720p than a 960x540 CCD in spatial offsetting. A further problem arises in spatial offsetting by way of noise apparently. I guess the DSP doesn't do its work without a certain amount of compensation.

The andromeda really does look great. I havent totally investigated it, partly because of the price, but it is a wonderful feat they have been able to pull off. TRUE 720p 4:4:4 uncompressed out of a DVX. The chip chart shows it all.
 
Oh I hear ya! I wasn't meaning my reply to be a rebuke! You make a very good and very legitimate point.

Certainly spatial offsetting comes with a price. I don't know enough about the gritty details to know precisely what those are though. It would be interesting to find out!

The Chroma issue is something I need to ponder some more. Bob Diaz made an interesting post on DVXuser today about the methodology of getting 4:2:2 from the camera. Seems right to me but I really need to sit down and ponder this some more. In any case:

Looking in the vertical direction the pixels would be as follows:

Scan line 1, Green Pixel goes for 2 lines down
Scan line 2, Blue and Red Pixels goes for 2 lines down
Scan line 3, Green Pixel goes for 2 lines down
Scan line 4, Blue and Red Pixels goes for 2 lines down
...
Scan line 1079, Green Pixel goes for 2 lines down
Scan line 1080, Blue and Red Pixels goes for 2 lines down

While we have 540 green scan lines of pixels, it's easy to forget that we also have 540 red and blue scan lines of pixels OFFSET BY 1/2 a CCD pixel. This means that every scan line of 1080 receives new color information.

Thus, a green screen clip would be OK and 4:2:2, because in the vertical direction there is new color information. There are three cases that can be made here:

(1) Green - Red or Red - Green: New color infromation is found on every scan line.
(2) Green - Blue or Blue - Green: New color information is found on every scan line.
(3) Blue - Red or Red - Blue: New color information is found on EVERY OTHER SCAN LINE.

So, don't use Blue Screen, use Green screen for the full 4:2:2 color.

Bob Diaz
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While there are 540 vertical green pixels, I forgot to add how the scan lines between the vertical green pixels are generated. This holds true for the horizontal direction too. To understand, look at the following ASCII Text "Drawing":

|G1 |X1 |G2 |X2 |G3 |X3 |...
|Y0 |R1 |Y1 |R2 |Y2 |R3 |...

When 960 Green pixels are converted to 1920 green pixels, the space between G1 (Green Pixel Number 1) and G2 is calculated as follows: X1 = (G1 + G2) / 2

Likewise, X2 = (G2 + G3) / 2 ....

While this does NOT increase the green detail, it does generate transition pixels. If G1 and G2 = 100% Green, X1 must be 100% Green. IF G2 is 100% Green and G3 is 0% Green, X2 would be 50% Green. This gives us some transistion effect.

Notice that where X1 apperars, R1 (Red Pixel Number 1) appears. On a Greenscreen clip with red or blue on a greenscreen, the new color information appears. In this case, where we see X2, R2 appears with a change in the color information.

While my ASCII Drawing shows it in the horizontal direction, just turn your monitor on its side to see the drawing in the vertical direction. At X2 we have transitional information in the Green and Red color information appearing. This provides the 4:2:2 color changes we need for a good key.


Bob Diaz

So much to ponder. I'm too tired to think about it tonight!

The andromeda is certainly an awesome achievement! It will be interesting to see what camera they decide to mod next and what sort of resolution they can pull from it! Playing around with uncompressed 4:4:4 images is SOOOOO nice! Maybe one of these days I'll get one.
 
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