… (and 4K Video)
by Ron Dawson
When I first sat down to write this review, I was in a quandary. What could I contribute to the Panasonic GH4 conversation that has been going on since the beginning of this year? My research was quickly swept into an acronym, spec, and nomenclature-heavy stream of information. Then I stumbled on a forum discussion about the claim that the 4K 4:2:0 8-bit video captured by the GH4 could be converted to 2K 10-bit 4:4:4 color space when transcoded to CineForm or ProRes.
If your eyes glazed over reading that last sentence, I’m not surprised. I consider myself a technically capable and informed filmmaker, and I’ve been doing it professionally now for more than a dozen years. I have instructed on the topic for a number of media outlets and national seminars, and even I felt tech-timidated. Photographers who are just learning video don’t need to be dunked into the deep end head-first like that.
Here are five short GH4/4K nuggets of information that will give you enough information to understand and follow the reviews and information out there and to give you the foundation to make an informed decision when considering this camera and other 4K technology.
1. Two flavors of 4K. There’s true 4K, specifically 4,096x2,160-pixel resolution (Cinema 4K), and then there’s Ultra HD (aka UHD), which is 3,840x2,160. UHD is four times the resolution of the standard HD spec: 1,920x1,080 (twice the length and twice the height). Most consumer TVs are UHD.
2. Micro Four Thirds sensor size. The GH4 is a Micro Four Thirds (MFT) sensor size, which has viewing area of 17.3x13.0mm (21.6 mm diagonal). This is important to know because of the crop factor (just over 2X). Here’s how it compares to other DSLRs.
Now before you write off this camera because of the tiny crop size, consider that an MFT sensor is larger than Super 16mm film, a format that was used to shoot part of Darren Aronofsky’s Oscar-nominated feature “Black Swan.” Many other well-known feature filmmakers have shot some classic films on Super 16 (e.g. Spike Lee’s “She’s Gotta Have It,” Aronofsky’s “Primer,” Robert Rodriquez’s “El Mariachi,” and Kevin Smith’s “Clerks”). My point: don’t let sensor size prevent you from making a choice to use a camera, unless there is some very specific aspect of a smaller (or larger) sensor that is truly significant.
For instance, larger sensors do have a shallower depth of field, so if for any reason you need super shallow DoF, a smaller sensor could be an issue.
Another point about MFT sensors worth noting is that there are so many lenses and lens adaptors already out there that can fit these cameras. The Metabones Speedbooster is a popular adapter that will allow you to connect full-frame lenses. They won’t make your field of view full-frame, but you’ll get a field of view closer to an APS-C (1.6X crop).
3. Recording format and quality. The biggest appeal of this camera is its ability to record 4K (both Cinema and UHD) directly to an SD card. When I was first using the camera, I had a heck of a time finding out how to do that. I discovered there are two menus you need to set. Recording Format (either AVCHD, MP4, MP4 LPCM, or MOV) and Recording Quality. It is in the Quality menu where you make the selection for 4K.
SIDEBAR: Format and quality primer
Here’s where I’d like to provide some filmmaker insight that may cause some of the aforementioned head-spinning. You’ll notice that the GH4 has literally dozens of format and quality settings:
Where on earth do you start? Here’s a quick primer:
Mbps is Megabits per second. The higher the number, the better the quality of the video. To give you perspective, the Canon EOS 5D Mark II h.264 video is approximately 45Mbps. The Nikon D7100 is in the neighborhood of 24Mbps. Traditional HD camcorders produced in the early to mid-2000s were also in the mid-20s.
All-I is “intra-frame” compression and IPB is “inter-frame” compression. The former looks at and compresses each frame individually. IPB looks at frames before and after and bases its compression on changes in the image. Theoretically, All-I will give you a better quality, but takes up more space and processing power. Which is why you’ll notice that none of the 4K formats are ALL-I. If you’re concerned about file sizes (i.e. hard drive space or SD card size) and processing power (for instance, if your computer is older), then stick with IPB formats.
The formats are AVCHD, MP4, and MOV. These are all what’s called “wrappers.” In the world of video there are codecs (how the image is compressed) and wrappers (the format the compressed video is placed in). The GH4 uses for the aforementioned wrappers for its H.264 compressed video. (Note: the MP4 wrapper here should NOT be confused with the MPEG4 codec.) You can have any number of different codecs for any one kind of wrapper. On the GH4, you’ll find the 4K quality resolution settings in the MP4 and MOV formats. AVCHD is a format common in consumer camcorders and lower end cinema cameras like Canon’s C100. It provides relatively high quality footage with a low Mbps compression rate. It can be tricky editing AVCHD footage, though, depending on which editing software you use. It’s not as easy as just dropping clips into a folder. AVCHD files are self-contained in a “Package.” Just about all the current versions of the major editing programs can “decode” this package and extract the videos you need. But each handles it differently. Know how you’re editing program works before choosing AVCHD.
LPCM and AAC are different audio compression formats. Frankly, I wouldn’t make any kind of decision on which format to choose based on this. If you’re using this camera to record video, and you need audio too, even though this camera will allow you to record (and monitor) audio, I still highly recommend using an audio digital recorder. Note that when choosing a format though, if you decide to go with the MP4, the LPCM option is best suited for video you want to edit later.
4. High Speed Recording. For my money, in addition to the 4K recording capability, another huge benefit of this camera is the ability to shoot slow motion IN CAMERA, and at full 1080p resolution. As a quick review: most of you will most likely be shooting in either 29.97 frames per second (aka 30p), 23.98 fps (aka 24p) or 25 fps if you’re in a PAL country. You can always slow down video in your editing software, but this reduces the quality and can make it look muddy. To achieve true slow motion with better quality, you need to shoot at a frame rate higher than the rate in which you’re editing. Most traditional DSLRs have been able to shoot up to 60 fps, which in a 24 fps project will yield 40% slow motion (24/60 = 40%). However, they have to drop their resolution down to 1,280x720 (aka 720p) in order to do that.
The GH4 allows you to record up to 96 fps in camera using the Variable Frame Rate (VFR) function. In fact, using this function, you can step your frame rate anywhere from 2 fps (which will give you a sped up video equivalent to 1200% speed at 24p), up to 96 fps, giving you 25% slow motion at 24 fps. All at full 1,920x1,080 resolution.
The VFR has to first be turned on in the format menu (either MP4 (LPCM) or MOV mode). Once you’ve set the format, you must change the Quality setting to 1080p at either 29.97 or 23.98 fps. You then exit back to the Motion Picture menu to turn VFR on.
What is very cool about this feature is that the GH4 will now shoot in the target 24 fps, but take into account the VFR setting, in effect, giving you slow motion in camera. Usually, you have to shoot at the higher frame rate, then change that frame rate to your project frame rate in your editing software. This is known as “conforming.” In short, by using GH4’s VFR feature, you don’t have to conform your footage. It will be imported into your editing software already slow.
It’s worth mentioning that you can still shoot regular high speed rates (i.e. 60 fps) at full 1080p, then conform later if you like. Why might you do that? Because the VFR functions are only available at the 100Mbps compression level (remember, the higher the Mbps, the better the quality). In the MOV mode, you can shoot up to 60 fps (technically, it’s 59.94) at 200 Mbps, All-I. If you need that extra quality and you don’t need slower than 40% slow motion, you might select this in lieu of the VFR.
5. Downscaling 4K to 1080p. As amazing as it may be to shoot 4K in camera, the truth is, most people do not have the ability to view videos in 4K. Unless you’re shooting something to be shown in a movie theatre, a full-sized 4K video will be useless to your client. But, fear not. There are two very significant reasons why shooting in 4K is better, even if your final output is traditional 1,920x1,080. And both are related to downscaling the video.
If you take a 4K video and edit it in a 1080p project, you now have a video that is 4X the viewing space. That gives you the ability to “push in” for close ups or reposition your image without losing quality. Here are three screen shots from a video I shot at UHD 4K to illustrate:
A 4K UHD image set to 50% of the video size (which fits perfectly into a 1080p project)
Here’s the same shot, but with the video size adjusted to 75%
And here’s the shot at 100%, giving me a nice close-up of the subject.
It’s not uncommon for commercial video jobs to set up two cameras, one for the wide shot and a second for the close up. If you shoot in 4K, you can get both in one shot. Or, do like I did, and use the second camera for a super wide shot. (My second camera was a Canon C100 shooting at 1080p, ungraded using the Wide Dynamic range profile).
Just think about all the editing options afforded you by having one of your angles shot at 4K resolution.
The second benefit of shooting in 4K actually relates to the head-spinning experience I mentioned at the beginning of this article: the ability to convert the 4:2:0 8-bit 4K video to 10-bit 4:4:4.
As I promised, my goal with this piece is to prevent you from being overwhelmed with all the technical jargon you may not be familiar with if you’re not a classically trained cinematographer (or a color scientist or mathematician). So I’ll keep this simple as possible.
Most DSLRs shoot in a 4:2:0 color space. This is a ratio of luminance and chroma (Wikipedia: Chroma subsampling). Again, the higher the numbers, the better (4 being the highest). The other color space combinations that are popular in the video world are 4:2:2 (as in ProRes 422) and 4:4:4 (or even 4:4:4:4, with the fourth 4 representing an Alpha channel).
Furthermore, the color depth of the GH4 video is only 8-bit (as opposed to 10-bit). Many Professional Photographer readers are well familiar with bit depth. Without getting into all the math, 10-bit is exponentially higher than 8-bit.
The theory is that if you transcode (i.e. convert) 4K footage to a ProRes 444 or CineForm 444 codec, the 4X resolution, when compressed down to 1080p, actually yields a richer color space. The extra pixels, in essence, increase your chroma values (the 2 and the 0), so that 4:2:0 becomes 4:4:4 (FYI: CineForm is created by GoPro and is most common on Windows machines whereas ProRes is common on Macs). The math for this actually works out. However, there is still debate on whether you actually get a 10-bit image from an 8-bit video. But it doesn’t matter. The 4:4:4 color space will give you a higher quality 1080p image than if you shot the video at 1080p. This will allow for better color grading or motion graphics work.
I ran a test where I compared 4K footage (transcoded to ProRes 4444 at 1,920x1,080) to 4K 4:2:0 footage dropped in a 1080p timeline. I then applied a Curves filter to it and adjusted some of the color values. The transcoded footage is on the left. The 4K footage (dropped in the 1080p timeline) is on the right.
If you click to view the full-size image at 100%, you should be able to see a noticeable quality difference.
(You can download the 200% image on my blog and check it out at http://j.mp/ddmag-gh4test1.)
You’ll need to use a program like MPEG Streamclip (squared5.com) or Apple Compressor, or GoPro’s CineForm to convert the footage. But it’s well worth having that extra color quality, particularly if you plan to do a lot of color grading and/or motion graphics work.
The Final Verdict
In my opinion, this is an amazing camera and deserves serious consideration. I definitely plan to use it for my shoots for all the reasons I mentioned above. And what I haven’t mentioned yet, which you likely already know, is that it’s only $1,700 U.S. (That boggles the mind!) Still, I strongly encourage you to rent it first. Lensprotogo.com is my go-to rental house, and they were kind enough to loan me the camera for this review (Shipping is included in their rates and that every order ships in Pelican cases. Using the code x180 will give you a 10% discount). Whoever you use, there’s no reason why you can’t invest the time and money to at least try this camera out.
I encourage you to do more research. Hopefully this article will provide some insight, fill in the knowledge gaps, and make your exploration all the more effective.