JVC GZ-HD7 "pre-review" highlights

[Steve Mullen]

1) The JVC GZ-HD7 (MSRP of $1,799.95) features a three CCD imaging system. Street price is about $1,300.

2) Each 1/5-in, 16:9 CCD has 570,000 elements that are progressively scanned every 1/60th second. Analog RGB signals from the CCDs are converted to digital data using 14-bit A/Ds. The Blue and Red CCDs are offset by one-half pixel from the Green CCD along both horizontal and vertical axes. Although the HD7 records only interlace video, progressive scanning CCDs are integral to generating 1952x1096 pixel frames at 60Hz from 530,000 (976x548) CCD elements. On alternate scans, 540-odd or 540-even lines from the 1096-lines become interlace fields. Each pair of fields is packed into a frame-buffer and encoded at a rate of 29.97fps.

3) The GZ-HD7 supports three MPEG-2 encoding modes: Full HD mode records five hours of 1920x1080i VBR at up to 30Mbps (26.6Mps average); the “HDV equivalent” mode records five hours of 1440x1080 CBR at 27Mbps (the limit of D-VHS); and the SP mode records seven hours of 1440x1080i VBR at up to 22Mbps. (For the latter two modes, each line is down-scaled to 1440-pixels before encoding.)

Stereo audio is encoded as MPEG-1 Layer 2 (MP2) at 384kbs. The video and audio elementary streams are multiplexed into a Transport Stream where each Data Packet has 192-bytes rather than the 188-bytes found in “.M2T” files. This type of stream is called “.M2TS” and the files are given a .TOD extension. A shock-resistant 1.8-inch 60GB harddisk records the data stream.

4) Up to 25 minutes of SP video can be recorded to a 4GB SDHC card so the GZ-HD7 is able to also perform as a sold-state HD camcorder. This opens the option to record video in physically demanding situations such as skydiving. (It’s not known if the HD7 can use the 8GB SDHC card coming later this year.)

5) JVC uses the same resolution CCDs and employs similar pixel-shift technology as does Panasonic for its DVX200 P2 camcorder. Therefore, I used my math model to estimate the dynamic resolution of the GZ-HD7. I altered my model to deal with the HD7’s greater horizontal recording bandwidth (1440- and 1920-pixels) compared to the DVX200’s limited (960- and 1280-pixel) recording bandwidth. While pixel-shift technology is able to double the number of pixels along each axis, it is only capable of increasing resolution by about 115-percent. The HD7’s resolution is equal to the four times more expensive Panasonic HVX200 P2 camcorder: 560 TVL/ph and 540 TVL.

6) Using Photoshop to check frame grabs I concluded that although Full HD mode does not provide additional horizontal resolution, its greater luma and chroma recording bandwidth provides cleaner video with no aliasing. However, the quality difference is slight—so if your editing workflow requires HDV equivalent video, you should not hesitate to use 1440CBR mode.

7) With the camera’s Sharpness set at mid-point (default), the image has minimal edge enhancement artifacts in any recording mode. To subtly increase video clarity, I incremented sharpness by 1-tick. For the remainder of my testing, I used Full HD with Sharpness set at +1.

8) Shutter Priority Mode
You set Shutter-speed by pressing the S button—at which point you’ll see the current speed displayed—and then use the Setting Dial to increment or decrement shutter-speed from 1/2- to 1/4000-second.

9) Aperture Priority Mode
Similarly, you set Aperture by pressing the A button—at which point you’ll see the current aperture displayed—and then use the Setting Dial to increment or decrement the iris from 1.8/1.9, 2.0, 2.8, 4.0, 5.6, to 8.0.

10) Shutter and Aperture Mode
You can also independently set both shutter-speed and aperture. Doing so automatically locks exposure. Because the aperture has no mid-stops, I recommend an alternate technique.

11) Exposure Bias Mode
First, set the shutter-speed. Now the camera’s AE system adjusts the aperture close to the correct exposure. Then press the BRIGHT button to enter Exposure mode. You’ll see the current exposure bias displayed.

Use the Setting Dial to decrement exposure in 1/3rd-stop steps until only unimportant highlights have a faint coating of 100 IRE zebra. (I previously confirmed that brightly colored and white objects could be captured at 100 IRE—the camera’s recorded limit—without bleaching-out.)

For backlit situations, I increment exposure in 1/3rd-stop steps up to the point before zebra appears on the subject.

To fully lock exposure, press and hold the Setting Dial for several seconds.

12) Fujinon supplies the Everio’s 10X optical-zoom lens that maintains nearly the same brightness (F1.8-1.9) throughout its f=3.3mm to 33mm optical zoom range (a 35mm equivalent of 39.5mm to 395mm). Unlike most lenses, the Fujinon seems to have no Lateral Chromatic Aberration.

13) To engage Focus Assist, press the Focus Assist button. The 207K-pixel, 2.8-in, LCD and large 0.57-in, 269K-pixel color VF will now switch to B&W. Use the wonderful wide rubber ring on the lens to adjust focus. Areas in sharp focus will be outlined in red, blue, or green.

14) When you plug in an external mic to the 1/8-inch stereo “power-plug” jack, dual level meters are displayed. The HD7’s audio limiter effectively prevented clipping. The AV jack can be used, with an adaptor, as a headphone jack.

15) The GZ-HD7 can capture 1920x1080 16:9 stills or 1440x1080 4:3 stills either to the disk or to an optional SD/SDHC memory card. All the exposure modes possible with video shooting can be used when shooting stills. You can shoot in color, sepia, and B&W. Zoom, however, is limited to 10X.

The camera’s Photo mode has several useful options: ISO can be set to 100, 200, 400, or to Auto; Continuous Shooting (approximately 2 per-second); and Auto-bracketing (+0.3 EV, 0 EV, -0.3 EV). When viewing a still, if you press the INFO button twice, the HD7 will display a histogram with photo data: Shutter-speed, Aperture, and ISO.

16) The Everio is equipped with three digital interfaces: i.LINK, HDMI (1080i, 480i, 480p) and USB. When the “Video/S Output” menu is set to 16:9, output is anamorphic. When set to 4:3; output is letterboxed.

17) Based on a menu setting, the i.LINK port can output either “DV25” or “MPEG-2” (HDV equivalent) from a Playlist. (MPEG-2 can be output only from video shot in 1440CBR mode.) The DV25 data stream can be recorded as anamorphic 4:3 video by a DV camcorder/VTR, DVD recorder, or NLE. FCP captures a DV stream as a series of shots into one file. I was able to capture MPEG-2 data streams with FCP. Capture using AIC and HDV Presets resulted in a file per scene. Interestingly, I was able to clone 1440CBR data streams to a Sony 1080i HDV VTR.

18) After several months of testing—including an informal comparison with an HDV camcorder three times more expensive—I came away very impressed with JVC’s GZ-HD7. Given it’s incredibly low-cost, for those who are willing to invest time to learn how to use its many features, it is a great value.

More about editing in a few weeks.

[Kaushik Parmar]

Steve Mullen,

Thanks for your notes, I am using this GZHD7 since last three months and I am happy. I always do auto shooting, since I don't know much about settings, I appreciate if you brief me all those tiny buttons and how it works. Can you please tell me proper manual settings, ideal settings?

Thanks,
Kaushik

[Jack Zhang]

The video and audio elementary streams are multiplexed into a Transport Stream where each Data Packet has 192-bytes rather than the 188-bytes found in “.M2T” files.

So that's why VLC can't play AVCHD files... It reads the TS as 188 instead of 192. Someone better send this to the VLC dev team.

[Bruno Donnet]

Concerning the Full HD mode (1920x1080):

Originally Posted by Steve Mullen

6) Using Photoshop to check frame grabs I concluded that although Full HD mode does not provide additional horizontal resolution, its greater luma and chroma recording bandwidth provides cleaner video with no aliasing. However, the quality difference is slight—so if your editing workflow requires HDV equivalent video, you should not hesitate to use 1440CBR mode.

IMHO, one of the other main interests in the Full HD mode is its VBR mode: if the global resolution is quite the same than with the 1440CBR mode (you say even a little better), I would hope that the resolution is better during scenes with fast movements than with the CBR mode.
Have you test it? (I know that It's not abvious to make a comparative test because you have to reproduce the same movements...).

[Steve Mullen]

Originally Posted by Bruno Donnet

Concerning the Full HD mode (1920x1080):
IMHO, one of the other main interests in the Full HD mode is its VBR mode: if the global resolution is quite the same than with the 1440CBR mode (you say even a little better), I would hope that the resolution is better during scenes with fast movements than with the CBR mode.
Have you test it? (I know that It's not abvious to make a comparative test because you have to reproduce the same movements...).

Good question. Water rippling in fountain -- I saw no difference amoung all modes. Using traffic zooming by right up close, there were no differences. The only blocking artifacts I saw were on very bright red cars. But all modes had the same amount.

So although VBR "should be better" I didn't see it. But this, as your point out, is not EZ to compare without three camcorders running at once.

I was most interested that recording to an SD card looked just like recording to disk. Which makes me wonder just how much better is XDCAM HD over HDV. Is it possible that people believe XDCAM HD "must be better" -- has anyone compared them?

[Michael Jouravlev]

Originally Posted by Steve Mullen

Although the HD7 records only interlace video, progressive scanning CCDs are integral to generating 1952x1096 pixel frames at 60Hz from 530,000 (976x548) CCD elements. On alternate scans, 540-odd or 540-even lines from the 1096-lines become interlace fields. Each pair of fields is packed into a frame-buffer and encoded at a rate of 29.97fps.

Does this mean that HD7 does not require deinterlacing as its interlaced stream is essentially a sequence of segmented frames? And the frame grabs have no jaggies too?

[Steve Mullen]

Originally Posted by Michael Jouravlev

Does this mean that HD7 does not require deinterlacing as its interlaced stream is essentially a sequence of segmented frames? And the frame grabs have no jaggies too?

The camera captures frames at 60 per-second. So the can be differences between frames.

Each frame is converted to a field by recording -- on alternate frames -- odd OR even lines from each frame.

So the recorded video IS interlaced video.

[Michael Jouravlev]

Originally Posted by Steve Mullen

The camera captures frames at 60 per-second. So the can be differences between frames.

Each frame is converted to a field by recording -- on alternate frames -- odd OR even lines from each frame.

So the recorded video IS interlaced video.

I see. Um... what are the benefits of this approach besides that the imager is future-proof for 1080p60 recording format/media?

Could it be that JVC simply reused 60p technology from 720p model in the 1080i model just to save money on R&D? On another hand, having the existing progressive imager and the 720p codec, JVC could have allowed 720p60 recording as well. Seems that they crippled their product deliberately.

[Steve Mullen]

Originally Posted by Michael Jouravlev

I see. Um... what are the benefits of this approach besides that the imager is future-proof for 1080p60 recording format/media?

Could it be that JVC simply reused 60p technology from 720p model in the 1080i model just to save money on R&D? On another hand, having the existing progressive imager and the 720p codec, JVC could have allowed 720p60 recording as well. Seems that they crippled their product deliberately.

The chip uses the "same" technology used by Panasonic for its HVX-200. The explanation of why 60p CCDs is long. I do cover the why/how in my book for those who are really interested.

Yes -- 720p50/720p60 could be obtained from these chips, but I really do not think the consumer group cares at all about progressive. Now it's possible 1080p501080p60 could also be obtained. That is more likely where they will go in a future generation. But, that requires the entire DSP run at 50p/60p which is likely not the case now where it runs at 25p/30p.

My book has a Chapter on converting 1080i50/1080i60 to 720p50/720p60. I wrote it ONLY for those shooting ProHD. But, I now realize that those of us who like editing 720p could use the same information.

Let me experiment a bit as this would allow me to intermix my HD1's 720p30 video in a Timeline. I'll post more when I know more.