Color Correcting Canon 7D Footage

A frequent concern about shooting to a heavily-compressed digital format—something the DV Rebel often finds herself doing—is the degree to which the footage will be “color correctable.” Will the shots fall apart when subjected to software color grading? Or will you be able to work with the footage as fluidly as you tweak your raw stills in Lightroom?

It’s a valid concern. The movies that the current crop of HDSLRs shoot are highly compressed. This compression is perceptual, meaning that it takes advantage of visually similar colors and shapes, and represents those regions with less accuracy than the detailed and varied parts of the image. This makes perfect sense, but often in color grading one seeks to enhance color contrasts—to make a face pop off a similarly-colored background for example—and so you may well create high contrasts between colors that were once nearly identical, and as such were given short shrift by the camera’s compression.

You might have noticed a similar phenomenon in audio. An low-bit-rate MP3 that sounds decent enough can suddently sound awful after even a tiny amount of EQ. Another case of perceptual compression limiting your options.

While you will never find as much data and detail in your HDSLR video as you do in that same camera’s raw stills, the H.264 movies created by the Canon 7D, 5D and 1D Mark IV will withstand some massaging in post. Here are some tips (similar to those found in greater detail in The DV Rebel’s Guide) to help you get the best results.

• Shoot flat. If you read Flatten your 5D, you know that I am a proponent of setting up a “flat” Picture Style using the camera’s built-in controls. The same settings I specced out for the 5D Mark II apply to the 7D and 1D Mark IV as well, although with the 7D I’m less likely to use Highlight Tone Priority, as this setting can increase shadow noise, and the 7D is not as noise-free as the other Canon HDSLRs.
• Chose WB wisely. Use a white balance preset that gives you as nuetral an image as possible. Shooting with an incorrect white balance reduces your dynamic range, because you wind up with an image that’s prematurely blown-out in one color channel, dark and noisy in others.
• Expose to the right. Make the brightest image you can without clipping something important. A rule-of-thumb considered gospel by many photographers, but our reasoning is a bit different. Yes, we, like the stills guys, wish to avoid excess noise in the shadows, but that’s not our main concern. Remember that term perceptual compression. Dark areas of an image get less bits. If you underexpose, you’ll have to brighten the image in color correction, and you’ll reveal all kinds of nastiness the camera thought you’d never see.
• Do denoise. It doesn’t really matter what denoising software you use, but use it. When you carefully and subtly denoise your footage, you rebuild your pixels anew, which is especially nice when you follow the next tip:
• Work at high bit-depths. If you start with an 8-bit image and do a gentle de-noise, you’re blending pixels values together to create new colors. Although there’s no such thing as something for nothing, doing this at a higher bit-depth means those new colors have massivly more gradations than the original image. Your subsequent color work will hold up much better.
• Sharpen last. Your flat Picture Style removed the camera’s built-in sharpening. Add your own at the very last step. The amount you use will vary depending on the output medium, so test test test.

By folllowing these guidelines you can make good-looking shots even better with color correction. But what about a shot that isn’t so great to start with? Turns out there’s hope. Below is a 7D shot that I grabbed in an uncontrolled situation. In my haste, I underexposed, and used the “cloudy” white balance when I probably should have used tungsten. But with a little denoising, careful analysis of the colors in the image, and a Colorista Power Mask, I was able to rescue this shot.

Yes, you can color correct your HDSLR footage, and you should. Color correction can make a good shot great, and in a pinch, put an unusable shot back in the game.

Gearing Up

Nothing profound here, just some fun new gear mixing well with some trusty old gear into what for me is a “where have you been all my life” rig.

Pictured here is the Canon 7D with the venerable Canon 50mm f/1.4. It’s sitting on the skeleton of the Redrock Micro “Captain Stubling” rig, handles removed, and slipped into Redrock’s tripod platform plate. That’s sitting on a crusty old Bogen fluid head that I had lying around (the current equivalent in size would probably be the popular Manfrotto 701HDV).

That’s mounted to my new slider rig from Glidetrack. It’s the Glidetrack HD to be specific, and I chose the 1M length, which feels like the right balance of utility and portability for me. I’m more likely to use it for push-ins than for side-to-side motions, and when you’re using it for the “slow creep,” there’s only so long a slider can be before it shows up in your shot. There are a number of terrific options out there for slider rigs, but the Glidetrack was the right choice for me because of its minimal weight and mechanical simplicity.

Hovering above it all on the Noga arm is the Ikan V5600, which is a comparatively inexpensive, lightweight HDMI monitor. It doesn’t have quite the full 720p resolution the peaking features of the Marshall V-LCD70P, [CORRECTION, Mitch below pointed out that the Marshal is not 720p—in fact it has a lower resolution than the Ikan!], but it’s still quite usable for focus. The photo above lies in its streamlined simplicity—the power and HDMI cables for the monitor make it quite a bit messier in practice.

Speaking of focus, the Redrock Micro whip makes that a little easier when back-panning on the slider. The whips come in sets of three — shown below is the shortest of the bunch. The build quality on the Redrock whips is very good.

What’s missing obviously is a good set of sticks, or possibly two, to properly support the Glidetrack. I’m still shopping and open to suggestions.

Gear porn shots like these requires bokake, here courtesy of the Canon 50mm f/1.2L on my 5D Mark II, the price of which was recently lowered.

Disclaimer: I contributed to the design of the Redrock Micro Captain Stubling rig, which recently received a glowing review on episode 53 of the always awesome Red Centre podcast.

As always, I am grateful if you shop through any of the above links, or at the ProLost store 7D Cine page!

NOCTURNE of Events

Canon has proudly placed Nocturne on their website, echoing the up-down-up pattern Reverie experienced last year.

Astute ProLost readers will have noted that Nocturne has always been viewable on my YouTube account, since Canon never asked me to take it down, just Vincent.

As you will recall, Nocturne is a short film shot entirely in available light using two pre-release Canon 1D Mark IV HDSLRs.

Vincent Laforet wrote about the film here and here, and has a fresh update here, along with a behind-the-scenes video edited by Joseph Linaschke.

My making-of post is here.

The 1D Mark IV is starting to show up in peoples’ hands and looks to be a rockin’ solid action SLR with the autofocus that Canon shooters have long wished for. As I wrote here, it is undoubtedly $5,000 worth of stills camera. It’s probably not $5,000 worth of HD video camera, unless you very specifically need the unmatched low-light performance.

Which you very well might. It’s obviously awesome.

Just remember that the Mark IV has no ergonomic concessions to video shooting—not even a dedicated video start-stop like the 7D has. And while it has greatly reduced rolling shutter skew (Nocturne is ample evidence of this), the video aliasing/moiré is no better than that of the 5D Mark II (something you can also see in Nocturne).

You Didn't Believe Me

10 frames of a 7D resolution chart, shown here cropped 1:1, courtesy of Paul Lundahl of eMotion Studios (click the image to visit)

This article over at DVXuser caused quite a stir. Which is strange to me, because I’ve been telling you about this problem for a while now. Apparently a detailed, well-researched article with great visuals and clear explanations is more convincing than pithy quips and offhanded remarks. I’ll have to remember that.

The article by Barry Green is about the oft-reported “aliasing” artifacts in video from the Canon HDSLRs (5D Mark II, 7D, 1D Mark IV). Barry does a great job of backing up a few steps and defining the term aliasing.

Aliasing occurs when you observe, or sample, something infrequently enough that you create an impression of something that wasn’t there. Imagine a blinking light in a room with a door. You must open the door to check the status of the light. If you open the door often enough, you get a pretty good picture of the status of the light, maybe something like on, on on, off off off, on on on, etc. Your samples are frequent enough to accurately represent the light’s activity.

But imagine that you just happen to relax your light-checking to a frequency at which you see nothing but on. The light flashes once per second and you check on it once per second. As far as you know, the light is always on. Your infrequent samples give you a completely bogus picture of what the light is doing.

That’s temporal aliasing, because the insufficient sampling takes place over time. The classic cinematic example of this is the wagon wheel that seems to spin in reverse. Aliasing can also happen in spatial samples. For example, if you looked through venetian blinds at a zebra standing on his head, your partial sampling might reveal a white horse, or a black horse, depending on how the stripes lined up with the blinds.

So what does this have to do with Canon HDSLRs? The same thing it has to do with every digital camera. Every camera that uses photosites to create pixels has to deal with this venetian blind problem. There’s space between those photosites, and in that space you can miss out on important information about what was happening in front of the lens.

This is nothing new. We’ve long known that we shouldn’t wear detailed patterns or fine horizontal stripes when appearing on video. This despite the camera manufacturers’ inclusion of an Optical Low Pass Filter (OLPF), a very fancy term for a simple layer of diffusion atop the sensor designed to scatter the light a bit, so that the zebra stripe that might have slipped through the cracks will actually be spread to the pixels on either side of said crack. OLPFs work, but if they work too well the camera gets dinged by pixel-peepers as being too soft, so every camera company makes a judgment call about how much sharpness they’re willing to give up for less sizzling when a zebra does a headstand in a field of blowing grass.

The current crop of HDSLRs cheat in a big way to make video. Their sensors are not designed to blast an entire, full-resolution image out every 30th of a second. So Canon’s engineers (and Nikon’s and even Panasonics to some degree according to Barry) did what stills camera makers have always done with the “good enough” video modes on point-and-shoot cameras; they grab something less than every photosite. They look at the blinking light less often, and as a result they can pull off a whole picture at a rate speedy enough to make video.

But this picture is full of holes. And while the OLPF was designed to spread light between adjacent pixels, we’ve now dropped entire rows of pixels, so suddenly it’s insufficient by a huge margin.

What’s great about Barry’s article is that he shows you how this problem manifests itself on test charts (you know how I feel about those) and in practical use. But what’s even more shocking is that he reveals the actual resolution of these cameras. Thanks to the aliasing, it’s shockingly low. Yet the images appear crisp — and that’s Barry’s most artfully elucidated point: It’s precisely this infernal aliasing that makes the images seem sharp. If you fitted a 7D with an aggressive enough OLPF, the aliasing would disappear — along with any illusion that the 7D is a “full HD” video camera.

Some aliasing makes zebras appear stripeless. Some makes wagon wheels seem to spin in reverse. And some makes low-resolution images appear sharper than they really are.

So every HDSLR user needs to be aware of this and make a decision: Is that OK? Is the “fake detail,” as Barry repeatedly calls it, good enough for you?

For many, the answer is yes. As I have pointed out, the sex appeal of filmic DOF often wins out over technical shortcomings in shooters’ hearts, if not their minds.

Still, I have tried to warn you. I tweeted not long before Barry’s article that anyone pointing a 5D or 7D at a resolution chart is in for a nasty surprise. I also made mention of the Canon SLR’s low resolution in this post, which confused commenters, who responded that 1920x1080 was plenty. Of course it would be, but I was referring to the actual resolving power of the poorly-sampled images, which is much, much lower, as Barry empirically shows.

I even blogged this, over a year ago:

Let’s get something straight. The video from the Nikon D90 and the Canon 5D MkII is not of good quality. It’s over compressed, over-processed, over-sharpened, and lacks professional control. It skews and shears and shuts off in the middle of a take. It sucks.

I was really trying to warn you guys about this.

But you didn’t listen. It took Barry’s awesome article to drive the point home. Maybe it was his facts and figures. Maybe it was his patient explanations. Or maybe it was because he did not end his article with anything like what I usually say after decrying the downsides of these cameras. Stuff like:

What the D90 and 5D2 have done is show us that it’s no longer OK for video camera manufacturers, whether they be Sony or Canon or RED, to make a video camera that doesn’t excite us emotionally. Buttons and features and resolution charts just had their ass handed to them by sex appeal.

That Barry didn’t wrap up with something gushy like that led many readers to accuse him of anti HDSLR-bias, but I think those people are wrong. Barry is a 7D owner, and challenged one aspiring HDSLR-hater with this comment:

I’ve shot some (what I consider) really, really good looking stuff on a 7D. It’s capable of great results. And I’ve shot some trash on it too, and found it very frustrating for anything wide/deep focus. But it’s $1700! You’ve got to cut it a lot of slack for that!

All I’m doing is pointing out exactly how these things work. It’s up to you to decide whether your scenarios would work within their limitations. If you’re shooting faces, they can excel. The more that you can keep out of focus, the better they’ll do. The more that’s in sharp focus, the more potential for negative complications from aliasing.

They are not a magic bullet. They are not Red-killers. They’re not sharper than conventional video cameras. Keep that all in perspective, and use them for what they’re good for, and they can do astonishingly good things at an unprecedented low price point.

Nicely said Barry. All around.

For my part, I’ve focused on the positive aspects of the 5D Mark II and the 7D because I like where they are pushing things. But I do owe it to you guys to show you that I take this aliasing problem seriously. You need to understand it well to evaluate whether an HDSLR is right for you. And I would hate to give Canon the impression that we’re content with looking at the world through venetian blinds.