Color Matching a Canon C300 to an Arri Alexa

They said it couldn’t be done. Maybe, but I got close. How close? You judge…

I’m shooting more projects with the Canon C300 but none of the built-in looks greatly appeal to me. While trying to build my own custom C300 look at a local rental house I spied an Arri Alexa in the next stall over… and asked, “Can I put that next to this C300 for a while?” The results are really interesting…

IMPORTANT UPDATE: I’ve been receiving reports on Twitter that my daylight matrix may be turning reds a bit blueish in some cameras. I’ve replaced the daylight matrix settings with a new set that should help with the blueish-reds issue. Version 2 will appear sometime early next week.

My buddies at Chater Camera let me come in and experiment with their toys whenever they aren’t busy. I’ve been trying to build a new look for the Canon C300 for a while and I’d developed one that was fairly color accurate, but when I saw a a prep tech checking in an Arri Alexa in the next stall I asked if I could borrow it for a bit.

Adam Wilt (background) and I try to match a Canon C300’s color to an Arri Alexa. I’m staring at a Leader 5800 waveform/vectorscope.

I use a DSC Labs Chroma Du Monde 28 chart for my color tweaking. I know that their charts are the most accurate available, and so do camera manufacturers: they generally use this chart, or one of its variants, in the creation of their color science.

The Canon C300 offers a variety of matrices, each of which bend red, green and blue in ways that Canon deems pleasing. The Norm1, Norm2, Norm3 and Norm4 matrices are basically the same, as best I can tell. Cinema1 is meant to create a filmic look for viewing on Rec 709 displays. Cinema2 creates a filmic look when shooting for film output. Canon Log captures as much information as possible for post color grading and looks desaturated and flat during shooting as log is a storage format only and isn’t meant to be viewed directly. EOS Standard matches the look of Canon’s EOS still camera line.

Color science can be really complicated or really not. I’ve heard that one manufacturer’s color science requires 10,000 lines of software code while another requires only 100 lines. It all depends on the taste of those creating a camera’s look, and each manufacturer has their own idea of what constitutes pleasing color. On the one hand this is good: a camera’s colorimetry is as distinctive as a film stock, and it’s possible to select a camera for its look the same way we used to choose film stocks for their looks. On the other hand, if the client dictates which camera you’re going to use on a project it can be awkward if you don’t think the camera’s overall look is appropriate for the project… or if you just really, really like the look of a camera your client can’t afford.

I love the Arri Alexa look, even when shooting in Rec 709 WYSIWYG mode. I live and work in a secondary market–the San Francisco Bay Area–where clients can’t always justify the expense of an Arri Alexa. The next best thing is to try to replicate as many elements as possible of the Alexa’s look in another camera. This is impossible to do perfectly, but if I can achieve some percentage of this look then I’m happier on those occasions when I can’t get an Alexa. Fortunately most cameras give us the tools to tweak their looks somewhat so that we can bend their base look into something we find personally pleasing.

Canon does some very interesting things with their color science. I’ve noticed that most of the matrices (Norm1-4, Cinema1, Cinema2 and Canon Log) push red toward yellow so that red becomes an orange “fire engine” red, and blue is pulled toward green such that bright greens, like grass, become cooler in hue. One interesting side effect is that bright green grass becomes a little less distracting, so if you’re shooting people running through a grassy field the cool-hued grass doesn’t draw attention from the action. On the other hand, if you want to capture bright green grass you’re going to have a hard time doing so using several of Canon’s built-in matrices.

On the plus side, the one color Canon nails in every single matrix is flesh tone. That’s important as flesh tone’s hue is burnt into our brains and we know instinctively when it’s not right. If you’re going to get one color right, it should be flesh tone. Everything else can be nudged one way or the other to create a unique look as no one will ever notice that greens are a little cool or reds are a little orange unless they do a side-by-side comparison. Meanwhile there’s a subconscious part of our brains that either likes this look or doesn’t. Clearly a lot of people like this look or it wouldn’t exist.

The one matrix that doesn’t show a lot of extra manipulation seems to be the EOS Standard matrix. When I look at this matrix on a Chroma Du Monde chart the colors are very close to accurate, and there doesn’t appear to be any secondary color correction going on behind-the-scenes. (Secondary color correction, in this sense, refers to manipulating a selected range of hues separately from the overall look. It’s a correction that affects only a small color range that sits on top of the overall color science.) For example, all the other matrices show a strange inward curve in the secondary hues between blue and cyan, and no matter how I try to tweak those matrices I can’t get rid of that curve. It’s a fundamental part of the underlying color science and it can’t be defeated. EOS Standard is very straightforward by comparison.

Above: The Norm1-4 matrices and Canon Log matrices have an interesting “notch” where the intermediate hue between green and cyan is noticeably desaturated and distorted. There’s nothing I can do with the tools provided to remove that notch, and it impacts blue and green in interesting ways when I try to manipulate those colors in the user matrix.

Above: In the EOS Standard matrix the “notch” between green and cyan is gone: the hue between green and cyan falls on a line directly between those colors. All the primary and secondary colors fall on or close to their vectors, but red is farther from the center of the vectorscope than the other colors which means it’s really saturated by comparison. I find this very distracting in an image.

The matrix controls I work with are part of the “Matrix” submenu found in the camera’s picture profiles, accessed by pushing the CUSTOM PICTURE button on the side of the camera. Here you’ll find several useful controls such as preset matrix selection, gain (saturation), phase (global hue adjustment), and a bunch of numbers labeled R-B, R-G, B-R, B-G, G-B, G-R. These abbreciations stand for “red minus blue,” “red minus green,” etc. These controls add and subtract color signals from each other in order to create a look. Subtracting one color from another makes it more pure, or saturated, while adding one color to another makes it less saturated. As pure colors are generally more desirable than muddy colors, and subtracting one color from another results in greater color purity, positive matrix values result in color signal subtraction and negative matrix values result in color channel addition. (It makes sense if you think like an engineer.)

There are a number of elements that influence a camera’s look: the dyes in the color filter array that pass light to photosites on the sensor play a very large part in the look of the camera as they provide the basic building blocks from which a look is created, but the final look comes from the math of adding/subtracting those color signals to/from each other using matrix math.

The R-G, G-R, etc. settings are generally referred to as the “user matrix” as this is how Sony labeled these settings in their F900 camera and the name stuck. They sit on top of all the other color science that drives the camera. No matter what you do with those controls you’re always adding a look on top of another underlying look. That’s why I chose the EOS Standard matrix as my base look: it appears to be the simplest matrix the camera offers, therefore it is the easiest one to push around predictably.

Canon’s description of how their user matrix works, from the Canon C300 manual.

One important thing to understand is that the user matrix has no effect on neutral tones: white, grays and black. The color matrix is completely separate from white balance. You can zoom into a gray scale chart, white balance, throw crazy random numbers into the user matrix and nothing will change… until you zoom out and include color in the frame, at which point you’ll see that every color is completely wrong.

For a rough description of my matrix creation process, and to download my settings, turn the page…

According to my personal taste in color, the EOS Standard matrix has two fatal flaws. One is that it is way too saturated, but that’s easy to adjust using the “gain” control under the matrix menu. (I used that control to desaturate the EOS Standard matrix for this spot.) The other is that red is much more saturated than any other color, such that any red object in the frame becomes a real distraction. Other than that, the EOS Standard matrix reproduces Chroma Du Monde colors fairly faithfully. 

After placing the Alexa next to the C300 I white balanced both cameras on the chart and then matched their exposures by placing the chart’s 18% gray background at 40 IRE on the waveform monitor. The Leader 5800 waveform/vectorscope has an overlay function, so I captured an image of the Alexa’s vectorscope pattern and overlaid the C300’s vectorscope pattern over it. I then tried to manipulate the C300’s user matrix until its vectorscope pattern overlaid the Alexa’s pattern. In theory this meant their colors matched.

This is really tricky because all the user matrix settings interact. Changing one matrix value will affect multiple colors. For example, manipulating the G-R value changes green’s saturation (increasing or descreasing it) but also changes red’s saturation and hue. If I change red’s hue by a large amount then it will no longer appear red on a display, so then I have to use another control, maybe B-R, to pull it back–but that then changes blue’s saturation.

It’s quite a juggling act.

It took several tries and various approaches to get as close as I did. What worked in the end was to use the phase control, which simply spins all the colors in a circle around the vectorscope, to match the chart’s flesh tone patches (between red and yellow). Then I pushed the other colors around to make them match as closely as possible. Here’s what I ended up with:

The inner ring of colors is the C300; the outer ring is the Alexa.

Adam and I toggled back and forth between cameras while looking at real flesh tone, typically one of our hands placed in the center of the chart. The C300 really wanted to make flesh tones more red than the Alexa did, and portions of our hands that are normally redder than normal skin tone (like knuckles) blended beautifully into the surrounding skin on the Alexa but popped bright red on the C300. In the end I had to make two compromises to make flesh tone match:

  1. Red was so crazy saturated in the EOS Standard matrix that I couldn’t desaturate it far enough on its own, using R-G and R-B, without seriously messing up green and blue, so I had to desaturate red by reducing saturation overall. Therefore this matrix desaturates every color except for red when compared to the Alexa.
  2. I couldn’t get flesh tone on the C300 to line up with the Alexa’s flesh tone and the chart’s red target at the same time, so I compromised and made flesh tone a near perfect match while leaving the C300’s red shifted slightly toward yellow, making it a little orange. This also happens in most of the C300’s built-in matrices.

Here’s the final “match.” It’s not perfect, but flesh tone is very close. I couldn’t match the bright flesh tones and the darkest flesh tone patch at the same time as those are spread farther apart in saturation on the C300 than on the Alexa. Note: We matched cameras using the Rec 709 output on the Alexa but I recorded LogC, which I ran through Resolve’s LogC-to-Rec 709 3D LUT to create the chart and vectorscope images in this article. As a result the two cameras matched better live, using Alexa’s direct Rec 709 output, than do the colors translated through Resolve 9 Lite, which appear slightly different.

Alexa is inside, C300 is outside. Flesh tones match, but in order to do that I had to desaturate the C300’s colors overall compared to the Alexa. Note the C300’s red is a bit orange, which seems to be normal for this camera.

Because red isn’t exactly lined up on the red vector magenta is pulled off its vector a bit, making it a little too red. As there’s very little magenta in the world this doesn’t bother me overly much.

Green matches in hue, as does yellow. Cyan matches in hue but as it’s pulled in toward the center on the C300 it’s a little more desaturated, which affects green and blue saturation to some extent. Cyan is a very difficult color for most cameras to saturate, and the Alexa does a vastly better job of it than most.

Flesh tones match, which is the important bit, and for the most part all the other tones match in hue other than red and magenta. The rest of the C300 colors are desaturated, which is what I had to do to lessen it’s tendency to exaggerate reds in flesh tone. After matching the colors as close as we could on the vectorscope Adam and I switched between cameras while looking at flesh tone on a monitor and reduced matrix gain (overall color saturation) in the C300 until flesh tone closely matched the Alexa’s.

Most cameras render colors slightly differently under tungsten light than under daylight, and these cameras were no exception. Creating a C300 daylight matrix was a bit more complicated. I didn’t want to use actual daylight as that changes, and it was an overcast day anyway. I didn’t want to use HMIs or daylight Kino Flo tubes because those are “good enough” for most uses, but their color spectrums are not perfect. I opted instead to use filters to convert tungsten light to daylight.

The normal film filter used for this conversion, the 80A, read as too heavy on both cameras: the C300 white balanced at 7000K and the Alexa saw it as 6300K, according to their own internal Kelvin measurements. Internal CCT numbers generated by cameras are rarely correct, but they do indicate what the camera thinks it is seeing. If the camera thinks it’s seeing 7000K then there’s a good chance that there’ll be a difference between my settings created using that white balance and a normal daylight balance of 5500K.

We used ambient daylight filtering into the shop through a window to see how the cameras responded to actual 5500K light and both cameras white balanced at more reasonable CCT numbers, so I backed off to an 80B filter. (The 80A converts 5500K light to 3200K; the 80B converts 5500K light to 3400K.) The only two 80B filters available in the shop that day were made by different manufacturers, and while the Schneider 80B worked very well on the C300 the Formatt 80B resulted in a warmer white balance on the Alexa. I added a 1/8 Schneider CTB filter to the Formatt 80B on the Alexa and brought the two cameras within 400 degrees Kelvin of each other. Based on a camera comparison that we did after building the matrix that appears to have been close enough.

Alexa is inside, C300 is outside. Once again, most colors match reasonably well except in saturation, which had to be lowered on the C300. The C300’s flesh tone and red hues match the Alexa reasonably well. Red is a lot less orange.

The color image matched better live than through Resolve’s LUT. If we compare these two images alone, though, flesh tone is accurate in hue but not necessarily in saturation. This time I was able to match both red and flesh tone, but while yellow matches on the vectorscope it’s off a bit in the picture. Generally the hues of all the colors match better under daylight but the slightly reduced saturation in the C300 results in a lot of differences in saturation. Still, saturation is easy to adjust to taste in the field by manipulating the matrix gain control. (There’s lots of saturation left in the C300. Both tungsten and daylight matrices were matched at -29 or so in gain; normal gain is 0, and -34 looks severely desaturated. The gain control is non-linear, and adjustments beyond -32 result in dramatic decreases in saturation.)

What’s interesting is to look at the shape of the chart colors on the vectorscope under different CCT’s:

This is the Chroma du Monde under 3200K (really 3000K) tungsten light. Tungsten results in a thinner pattern than does daylight. This is probably because there’s very little blue in tungsten light so it’s harder to expand the pattern–and increase saturation–on the blue-yellow axis.

Tungsten light is very hard on cameras as the blue channel typically requires +6db of gain just to make its signal strong enough to balance with the other color channels. This is the equivalent of pushing the blue emulsion layer in a film stock by one stop, and is the reason the blue channel is always the noisiest channel under 3200K light.

This is the pattern under 5500K daylight. The blue-yellow axis is wider, meaning that both yellow and blue saturation has increased. This results in fuller color saturation across the reproducible spectrum. Silicon sensors are naturally “daylight balanced” because silicon is least sensitive to short wavelengths of light, like blue, so they perform best when the light striking them has a LOT of blue in it to compensate for this insensitivity.

It’s important to know this because some cameras hide these different responses to color temperature better than others.

You want settings? I’ve got settings, on the next and final page…

First, the standard disclaimer:

While I plan on using these settings myself for future projects, your mileage may differ depending on a number of factors including taste, camera software version, lens choices, etc. As a result I take no responsibility if you don’t like the results. It’s up to you to test these settings before you use them professionally to make sure they work to your satisfaction. By using these settings you indemnify me against any claims in the event that someone down the road doesn’t like how these settings look and that costs you money.

If everybody loves you as a result of these settings I’m happy to bask in the glow of your success.

NOTE: As I mentioned in an update to the front page, I received some complaints saying that the daylight matrix made reds look blueish on some cameras. I came up with a replacement daylight matrix while shooting with a C300 the other day so I’ve replaced the original settings below. I hope to have a new version of both matrices, version 2, posted by sometime next week that should work well on C100s, C300s and C500s.

Here they are:

Canon C300 Arri Alexa Color Emulation Matrices v1.0

Detail circuit settings are not included. When we compared camera detail we discovered that setting the C300 detail circuit to its lowest value resulted in an image that was still sharper than the Alexa. Adjust it to your own taste.

As color and gamma are completely decoupled in the C300 you can use this matrix with any gamma, although be sure to test this first to make sure the results are to your liking. I like Cinema1 and Cinema2 myself.

Don’t use these matrix settings with any matrix other than EOS Standard as you will get untested, unintended and unpredictable results.

One last very, very important note:

THESE SETTINGS WILL NOT TURN YOUR CANON C300 INTO AN ARRI ALEXA REPLACEMENT. I’ve attempted to replicate aspects of the Alexa’s colorimetry in a camera whose design and color science are completely different in every way, using very coarse tools whose settings sit on top of Canon’s proprietary color science. The C300 doesn’t have the subtlety of color that Alexa offers, nor can it match Alexa’s dynamic range, and it doesn’t duplicate that delicate Alexa softness that makes everyone and everything look great. On the other hand, the C300 is less expensive and much smaller and lighter, and is the perfect tool for certain projects.

If you own a Canon C300, if you can only afford a C300, if you need the mobility and size of a C300, use a C300. If you can afford an Arri Alexa, use the Alexa. Get the right tool for the right job.

You can download a PDF version of the settings here.

Thanks very much to Adam Wilt for his time and help, and to Chater Camera (especially Jay and Charlie) for allowing me playtime with their gear.

Disclosure: I have worked as a paid consultant to DSC Labs. If you’re interested in their charts, check out their website and read my article about their new film-style HD grading chart.

Art Adams | Director of Photography & Motion Picture Technology Consultant | 01/26/13 | www.artadamsdp.com

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Art Adams is a cinema lens specialist at ARRI, Inc. Before that, he was a freelance cinematographer for 26 years. You can see his work at http://www.artadamsdp.com. Art has been published in HD Video Pro,…