Panasonic Lumix DMC-GF1 Review

 
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Panasonic GF1 Video Recording

by Dave Etchells and Michael R. Tomkins
(Updated 9/15/09: AVCHD motion artifacts were the fault of VLC player, not the GF1!)

Panasonic's previous Micro Four Thirds camera, the GH1, introduced video recording capability to the line -- and most of that functionality has been carried over, with the biggest exceptions being the 1,920 x 1,080 pixel AVCHD / FHD mode, full manual exposure capability, stereo microphone, and external microphone jack. Importantly, though, the Panasonic GF1 retains the GH1's ability to autofocus during live video recording. At the time of the GH1's announcement, that was a truly unique feature among SLR-style cameras, and even today it's a rare camera that even tries to implement it, let alone does so usefully.

For video fans, much of the allure of the Panasonic GF1 is the ability to use a variety of lenses with it, opening a range of creative capabilities. The large size of its sensor relative to those of typical consumer camcorders means that you can achieve shallow depth of field with large-aperture lenses. The Panasonic GF1 also offers rather more control over exposure of its videos than the typical camcorder, although unlike the GH1 full manual control of video exposure isn't possible..

Depth of Field Control. This .MOV movie clip from the GH1 (NOTE: 35 MB download) shows the depth of field control you can achieve with the Panasonic GF1 using its kit lens. The video shows the effect on a macro subject of moving from the lens's maximum aperture down to f/22 and back again.

As with the GH1, consumers will doubtless find the key feature to be the Panasonic GF1's live autofocus during recording, though. Pros and advanced amateurs can "pull focus" (adjust the focus manually) while filming video, and indeed may well prefer to do so, considering focus to be another outlet for their artistic vision. Doing it well is very much a learned skill, though, and something very few people ever learn to do really well. Without live AF, consumers for the most part are reduced to only shooting things at a constant distance from the camera -- or to putting up with a lot of poorly-focused video. A lot of video-capable SLRs are certainly being sold to consumers these days, and having some video capability is certainly better than none, but for most consumers to make full use of a video camera, it really needs to be able to focus on the fly.

Arguably, this was what Panasonic had in mind from the very beginning of the Micro Four Thirds concept; a true "hybrid" camera that needn't make any excuses for its performance, whether shooting still or video imagery. When I was first briefed on the G-series concept by Panasonic's engineers in Japan, months before the initial announcement, a lot of my discussion with them revolved around the autofocus system. My concern had to do with whether contrast-detect AF could be fast enough to rival the performance of phase-detect AF systems in conventional SLR cameras. While they were certainly concerned about the AF speed for still photos, it turned out that a lot of the decisions made in the G-series AF system were actually driven by the needs of video recording: A critical goal of the G-series design was for the autofocus system to execute a complete AF cycle in 1/60 second -- because that's the basic frame time of an HDTV signal.


The Importance of the Lens. What the engineers were hoping to develop was not just a responsive still-camera AF system, but one that was fast enough to perform autofocus on the fly, while live video was being recorded. This was really a quantum leap beyond anything that had remotely been attempted in an interchangeable-lens hybrid camera prior to that time. To accomplish this, they needed a system and processor fast enough to read out a line of video data, compute the contrast magnitude for it, decide which way to move the lens, accelerate and move the lens and stop it at a precise location again, all within 1/60 second. The emphasis on stopping the lens movement is there because this turned out to be one of the tougher challenges. Accordingly, a good part of the ability of the GH1 and GF1 to autofocus during video recording depends on the lens you're using with it. Only certain lenses, marked as HD-capable will fully support live video AF, the first such being the (excellent) 14-140mm optic that shipped with the GH1 body as its kit lens. You'll generally be able to eke out at least some live autofocus from the Panasonic GF1 with other, non-HD lenses, but an HD-capable lens will prove faster and much more sure-footed than others. HD-rated Panasonic lenses also feature nearly silent autofocus mechanisms, so focus noise will be less audible on movie soundtracks. That said, you can put any lens that you can find an adapter for onto the Panasonic GF1 and shoot with it using manual focus.

There's another lens consideration that's important for video recording: HD-certified lenses for the Micro Four Thirds system have continuously variable aperture settings. That is, the camera can adjust the lens aperture smoothly across the entire range of settings. Most lenses can only vary their aperture setting in fixed steps. Such lenses will produce visible jumps in brightness if the light varies during video recording. (One way around this is simply to record in constant-aperture mode when shooting videos with non-HD lenses.)


Panasonic GF1 Video Basics: Speeds and Feeds

The Panasonic GF1 gives you two broad choices of video recording format, and several options for resolution and/or compression level within each of those file types. The table below lists these options.

Panasonic Lumix DMC-GF1 Video Options
AVCHD Lite Format (.MTS files)
Menu Designation
Resolution
Frame Rate
File Sizes

SH

720p
1,280 x 720

60p recording
(sensor output is 30 fps)
17 Mbps

~90-128 MB/min

H

720p
1,280 x 720

60p recording
(sensor output is 30 fps)
13 Mbps

N/A
(wait for full review)

L

720p
1,280 x 720

60p recording
(sensor output is 30 fps)
9 Mbps

N/A
Motion JPEG Format (.MOV files)
Menu Designation
Resolution
Frame Rate
File Sizes
(very approximate)

HD

1,280 x 720
(16:9 aspect ratio)

30 fps

~200-230 MB/min

WVGA

848 x 480
(16:9 aspect ratio)

30 fps

N/A

VGA

640 x 480
(4:3 aspect ratio)

30 fps

N/A

QVGA

320 x 240
(4:3 aspect ratio)

30 fps

N/A


AVCHD Lite vs Motion JPEG: Which to use? There are significant differences and trade-offs between the two different video formats. The Panasonic GF1's manual suggests using AVCHD Lite for movies that will be played back on your HDTV via the camera's HDMI connection, and Motion JPEG for playback on a PC. We've found this to generally be true, as our experience has been that AVCHD video looks much better when played on an HDTV than does Motion JPEG. For its part, AVCHD is not without its trade-offs, particularly when it comes to playing back or manipulating the files on a computer.

AVCHD Lite is a subset of the AVCHD specification, and identifies an AVCHD device that is limited to a maximum of 720p recording. Full AVCHD devices like the GF1's predecessor the GH1 are capable of either 1080i or 1080p, and indeed the GH1's FHD mode was captured as a 1080i (1,920 x 1,080 pixel) stream. It is this mode which the GF1 has dropped since the GH1. Given that the highest-quality 720p SH mode which remains available in the GF1 has the same 17Mbps bitrate as was used for the 1080i FHD mode, though, we doubt it'll be terribly missed, since the higher resolution came at the expense of decreased quality and increased artifacts.

AVCHD and AVCHD Lite both use an H.264 MPEG codec to compress the video stream, which achieves much greater compression than Motion JPEG, but requires more processing power to both compress and decompress. Recent-model computers with a good H.264 codec installed should have no trouble playing back AVCHD Lite video from the Panasonic GF1, but owners of older machines may find their CPUs struggling somewhat, resulting in jerky playback or dropped frames. Editing AVCHD likewise requires a reasonably powerful computer (at least by 2009 standards) and good editing software. On the other hand, as suggested by the manual, AVCHD playback from the camera to an HDTV via the camera's HDMI port works just great: HDTVs have very powerful custom processors built into them, designed to handle the rigors of HDTV decoding and display. By contrast, Motion JPEG (.MOV format) files from the Panasonic GF1 should open and play back just fine on most relatively recent-model computers. On older machines, with slow video cards or slow hard drives, you may still notice occasional hesitations in the playback, but you'll encounter significantly less than with AVCHD. Likewise, Motion JPEG files are much easier to edit on computers with only average processing power. The GF1's Motion JPEG files are limited to 2GB however, while AVCHD can be recorded up to the capacity of the memory card.

The difference in file sizes between AVCHD and Motion JPEG is pretty dramatic, though: Compression ratios will vary depending on the complexity of the image being recorded, but with highly-detailed subject matter, 720p resolution AVCHD Lite files can be as little as a quarter the size of Motion JPEGs for any given recording length. With more typical content, AVCHD files usually come in around half the size of Motion JPEGs. If playback on a less-powerful computer isn't an issue for you, and you want to record the maximum amount of video in the smallest amount of space, AVCHD Lite will be the way to go. At the highest quality settings (with 17 Mbps data rate), AVCHD Lite video files amount to only about 2.1 megabytes/second, or roughly 128 MB/minute. That's still a lot of data, but is nothing like the file sizes you'll see with Motion JPEG. At its lowest-quality AVCHD Lite setting, image quality with moving subjects will take a significant hit, but the GF1 will burn memory at a relatively parsimonious 65-70 MB/minute. At that rate, a 2GB memory card can hold up to 29 minutes of video.

All else being equal (and with subjects where only part of the scene changes from frame to frame), AVCHD Lite on the Panasonic GF1 will give somewhat better image quality than will Motion JPEG, but the differences are relatively small.

At the rollout event for the GF1, Panasonic provided several prearranged subjects for the journalists in attendance to shoot with the camera. One such was a very nice string quartet, which provided a good opportunity to evaluate both the GF1's video image and sound quality. The crops and videos linked below were shot at this event, using a prototype sample of the GF1: It's therefore possible that some image- and sound-quality aspects could be improved on production models, but based on our prior experience with the GH1, we believe that the results here will prove to be pretty representative.

AVCHD Lite Video Image Quality Examples

My first reaction to recordings of the string quartet was that perhaps I'd been overly harsh in my earlier evaluation of AVCHD's image quality, as seen on the DMC-GH1 camera. I'd been dismayed by motion artifacts in the AVCHD video, but the subject I was using for my evaluation (our dog Charlotte chasing her Frisbee) was one that involved a lot of movement, including rather rapid panning of the camera during filming. At first glance, the AVCHD output from the Panasonic GF1 seemed quite nice; very sharp and crisp-looking, and I didn't immediately notice any of the motion artifacts that had so bothered me in the GH1's AVCHD output. (More on this in just a bit, though.)

Video format image quality comparison
Motion JPEG
AVCHD Lite

In fact, while the differences were relatively subtle, it seemed clear to me that the basic video image quality in the GF1's AVCHD mode was better than that from its Motion JPEG recordings. The crops above are from a Motion JPEG and AVCHD Lite video taped within a minute or two of each other, from roughly the same position. The differences are indeed subtle (you honestly might never notice them while the video was playing), but they're definitely present: Edges and details are better-defined in the AVCHD crop, while some JPEG compression artifacts are visible in some parts of the Motion JPEG image. (Look particularly in the area along the upper edge of the cellist's right arm; fuzziness from JPEG compression artifacts is clearly visible against the flat tones of the wall behind her.)

Beyond the pixel-peeping of the crops above, the AVCHD video just appeared crisper and cleaner when playing, as compared to the Motion JPEG sample.

Unfortunately, after a few minutes of study, I once again encountered the motion artifacts I'd come to expect when playing back AVCHD files on my computer. - As it turns out, this was actually the fault of the decoder I was using for playback, rather than a problem with AVCHD itself.


AVCHD and Motion Artifacts

Nothing comes for free, so it should come as no surprise that there's a consequence for AVCHD's much smaller file sizes. The trade-offs are that AVCHD files require a lot more processing by the playback device to decompress and display them, and that software support for AVCHD isn't on par with that for Motion JPEG (at least as of this writing, in September of 2009).

There are a couple of different flavors of AVCHD compression, in terms of the amount of data that's recorded. The highest (and apparently somewhat rare) spec results in a data rate of 24 Mbits/second being recorded onto the media, while the more common specification produces 17 Mbits/second. As with the GH1, the Panasonic GF1 uses this latter specification. Either spec results in fairly extreme levels of image compression, which means you can encounter some pretty dramatic loss of detail if a lot of the scene is changing from frame to frame.

The most critical issue is how much of the frame changes between frames, because AVCHD uses a keyframe-based compression. That means that it records full image information (albeit still compressed) only every so often, and in between these "key frames," only frame to frame differences are recorded. It furthermore limits the recording to a particular data rate (the 17 Mbits/second mentioned above), so if there's a lot of change happening between frames, a lot of data can get thrown out. On the other hand, if most of the image is the stationary, with only a small portion of the subject in motion, detail remains pretty good all over.

It's important to note that this limitation in the amount of frame-to-frame motion that can be accommodated isn't in any way unique to the Panasonic GF1; it's a characteristic of any AVCHD device, although those using the higher 24 Mb/s data rate limit will do somewhat better.)

Motion Artifacts from AVCHD? - Results from VLC media player
When I fired up my AVCHD-capable video player program (VLC, version 1.0.1), I was disappointed to see the sort of blocky artifacts shown above. In the crop at left, the bow has just swept in front of the violinist's face, leaving a trail of blocky artifacts in its wake. In the same crop, the cellist's right hand and part of her arm can also be seen, also suffering from motion-induced artifacts. Some of these could occur over a larger area, with large chunks of a sleeve or hand suddenly flickering with a slightly different shade of the dominant color, before reverting. In the crop at right, the cellist's bow has just swept across a portion of the wall between the bow and the cello, again leaving a patch of chunky artifacts behind. As it turns out, though, these artifacts were produced by the player software, not the GF1!

It's interesting that the fairly extreme artifacts shown above didn't immediately leap out at me when I first viewed the GF1's AVCHD videos. They don't last on-screen very long, but while they're there, they're pretty obtrusive. Once I became aware of them, I saw them everywhere, and they became very distracting.

Previously, I'd thought that AVCHD artifacts would only be an issue when large percentages of the scene were changing from frame to frame. What these shots seemed to show was that any sort of rapid motion could induce these sort of artifacts, even if the motion involved represents only a limited portion of the frame.

I was really chagrined to see the dramatic artifacts shown above: AVCHD video definitely plays back better on HDTVs than does Motion JPEG, and the files that result are only half the size. It seemed a shame to have to choose between good HDTV playback or good image quality: Why couldn't we have both?

As it happens, we can: I was very happy to receive an email from reader Andrea Menzo shortly after posting the initial version of this page, pointing out that the otherwise-excellent VLC video player has a significant bug in its handling of motion decoding in H.264 video (the video encoding scheme used inside AVCHD files). Andrea suggested that I try the Handbrake program on my Mac, to translate the .MTS files to .mp4 ones that could be played back in QuickTime directly. I did so, and presto, the artifacts were gone! (Thanks again, Andrea!)

Artifacts Begone! - Results from QuickTime, via Handbrake
These crops show the same areas as above, but the .MTS files were first converted to .mp4 via Handbrake, and then played back in Apple's QuickTime. Much better!

The crops above match the previous ones, except this second set were made from the .mp4 file that was converted via Handbrake. As you can see, image quality is excellent, with no sign of the nasty artifacts that I saw originally.

AVCHD Player Differences II - Color and Detail
VLC Player
Converted in Handbrake
While VLC player has problems with motion artifacts, it does a bit better on absolute detail rendering. There are color differences between players as well.

Comparing the output of VLC player and material converted via Handbrake side by side, we can see that VLC's detail handling was just slightly better, and colors were different between the two. The actual color of the girl's coat was probably somewhere between the two shades shown here, so neither application entirely nailed it. Handbrake probably came a little closer, though. When it comes to detail, while it's easy to see minor differences while pixel-peeping static screenshots, it's almost certain that you wouldn't be able to see such differences in a live video stream.

Bottom line, while it's still probably a good idea to avoid very rapid panning in AVCHD mode (to avoid large frame to frame changes), there doesn't seem to be any reason to avoid it for files that will be viewed on a computer, provided you equip yourself properly to handle them. The first requirement is obviously a reasonably powerful computer, as AVCHD playback does require a good bit of processing to carry off. Equally important, though, is that you have a good-quality codec (coder/decoder) package installed, and a player that takes proper advantage of it.

Software for AVCHD Playback

As we've seen, the quality of AVCHD video viewed on a PC very much depends on the software you use for playback. The very popular open-source VLC media player application is fast and free for the downloading, but has major problems with motion artifacts in AVCHD video streams (at least as of version 1.0.1). These problems occur in both Mac and Windows versions of the app.

For more reliable playback of AVCHD files, we recommend the excellent K-Lite Codec Pack, which includes codecs supporting literally dozens of different formats. There are several versions available, ranging from Basic to Full and Corporate. We downloaded the Standard version and it worked like a champ with our GF1 video files. You can either use the bundled "classic" media player, or let your current DirectShow media player use the codecs from K-Lite.

On the Mac, options are a bit limited, as the current version of Apple's QuickTime doesn't support AVCHD files directly, and there don't appear to be any open-source players for the Mac platform with reliable AVCHD playback capability. The best solution currently (September, 2009) appears to be to use the excellent Handbrake video transcoder application to convert the GF1's AVCHD into .mp4 files, which QuickTime can read and play just fine. We used Handbrake's MPEG-4 (FFmpeg) video codec to convert the files linked below, plugging in an average bitrate of 17,000 Kbps, to match the 17 Mbps of the AVCHD spec (thereby avoiding throwing away any genuine image data). On a dual-core Intel Mac, transcoding is pretty speedy, and if you opt for two-pass encoding, the resulting mp4 files are actually a bit smaller than the original AVCHD ones.

Panasonic GF1 Audio Quality

Among the relatively few changes between the GH1 and GF1's video modes is the removal of the earlier camera's stereo microphone jack, and the replacement of the stereo microphone with a monaural one. While a shame, these changes were doubtless necessary in order to keep the GF1's body down to is impressively svelte proportions - while far from a heavyweight, the GH1 had a significantly larger body. The good news is that we found audio quality from our preproduction GF1 was actually surprisingly good, despite of the change to a mono mic.

Shooting the string quartet with the Panasonic GF1, I was amazed by the sound quality when I listened to the audio tracks on high-quality earbuds. The sound was crystal-clear, to the point that, in some clips, I could actually hear the reverberations from the rather long hall the group was playing in. It's a shame that there's no external audio jack, though, as that would give you so much more control over the audio pickup. As it is, the built-in mic on the camera tends to pick up quite a bit of sound from all directions, so it can be hard to exclude ambient noises from your audio. (Such as the clicking of still photographers' shutters, which are clearly audible on some of the video clips.)

The GF1 retains the wind cut filter that was offered in the GH1. As with that camera, it can be applied via an option on the GF1's Motion Picture menu. We haven't had an opportunity to play with this much, but it offers settings of Off, Low, Standard , and High, and did seem to cut wind noise somewhat when we used it on the GH1. (We didn't use the camera in any very windy conditions, though, so can't speak authoritatively on this feature.)

One important note about audio recording with the Panasonic GF1: The camera's exposure system lets you change the aperture while recording is in process, but sounds from the control dial used to effect the changes is clearly picked up by the audio track. Likewise, when using non HD-capable lenses the sound of autofocus operation is likely to be easily audible, although the noise level will likely vary with the specific lens model used. With no external microphone jack in the GF1, if you want to make on-the-fly aperture changes or use non-HD lenses and these sounds bother you, your only real alternative is to overdub an audio track from another source to hide the clicking.


Panasonic GF1 Live Autofocus Performance

As noted earlier, the Panasonic GF1 requires "HD-rated" lenses for best results with live autofocus during video recording, and it should be noted that neither of the kit lenses is HD-capable. In the manual, Panasonic notes that the speed of subject tracking may be compromised when using non-HD lenses in video recording, and as previously described, that autofocus noise will likely be picked up by the camera's internal microphone. Also, because it lacks the direct distance-measuring capability of a phase-detect AF system the GF1 can have trouble responding to too-rapid changes of subject distance. If the focal distance changes very abruptly (as in a quick shift from a foreground to background object, for instance), the camera can have difficulty figuring out how it should move the lens. It knows the scene is out of focus, but isn't sure whether to focus closer or further away. If the amount of mis-focus is extreme, it may end up "hunting" across the full focusing range of the lens, a very slow procedure. This is likely to be exacerbated by using non-HD capable lenses, but can be tamed somewhat by paying attention to how quick a focus shift one asks the camera to make: Sometimes, panning just slightly more slowly from foreground to background or vice versa makes for a big improvement in focus tracking.

Panasonic GF1 Sample Videos

Click on the links below to view/download our sample clips. You should have no problems playing the Motion JPEG files with most video players, including QuickTime. You may need to install an AVCHD Lite codec or player to view the .MTS files. (The VLC video player works across multiple platforms, and did a very good job of playing back the AVCHD files on our Intel-based Macs. Older platforms stuttered somewhat, but the results were better than any other player we tried.)

(NOTE that these are extremely large files: If you think you'll be inclined to want to refer back to them, please download copies to your local hard drive, to save our bandwidth!)

Panasonic GF1 Sample Videos
Motion JPEG
AVCHD Lite

(Shallow Depth of Field)
AVCHD version
.mp4 version

(Greater Depth of Field)
AVCHD version
.mp4 version
720p Videos. 1280x720 at 30 frames per second. (Click to play / download ~40MB MOV files, 15-20MB .MTS files, or 12-15MB .mp4 files.) Pretty good audio for a little hole on the camera's top deck, eh? (These videos were shot by Dave Etchells in Berlin on September 1, 2009 with a prototype Panasonic GF1 camera.)
Charlotte Video Samples
Motion JPEG HD (720p) sample Motion JPEG VGA (640x480) sample
AVCHD 720p samples below: Click to download;
must have AVCHD player installed on your computer
AVCHD 720p (SH)
Note that though Dave says "1080p" in the video file, it's actually 720p

Bottom line, the Panasonic GF1 is a great video-shooting tool, and both image and audio quality are impressive. If you have appropriate software to support it for your computer, AVCHD is a very compact video format, with excellent image quality, and it also plays back great on HDTVs via the GF1's HDMI output port. The Motion JPEG format is easier to edit on a computer, though, so you may find the trade-off of its larger file sizes worthwhile, if your video editing software doesn't support AVCHD well.

 

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