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By Pravit Gandhi··9 min read

How to grade C-Log3 footage from a Canon R5

How do you grade C-Log3 footage? Plain language: what the curve is, the three routes to a normal picture, and which one to pick on a Canon R5.

Do three things, in this order. First, tell your software the clip is Canon Log 3 and let it convert the picture to Rec.709, either through the editor's own color management, a color space transform, or Canon's own LUT. Pick one of those three and only one. Second, fix exposure and white balance so the shot sits where it should. Third, add whatever look you want on top. Almost everyone who says C-Log3 is impossible is doing step three before step one, or doing step one twice by accident.

C-Log3 in plain terms

Your sensor records far more brightness range than a television can show. Saved the way a television expects, the bright parts would clip and be gone. So Canon squashes it into a curve no display understands and hands you that. That is C-Log3. It looks grey and lifeless on purpose, and Canon's white paper says why: the curve "presupposes that the images will be graded at the post-production stage."

Canon Log 3 is not an upgrade of Canon Log 2, whatever the numbering suggests. The white paper's FAQ says so: "Canon Log 3 is not the successor to Canon Log 2 but the successor to Canon Log. It extends the dynamic range by the equivalent of one stop compared with Canon Log." It reaches 1600% dynamic range and keeps the shadow behaviour and 18% grey placement of Canon Log. On an EOS R5 it arrived in firmware 1.3.1, which Canon's notice describes as adding Canon Log 3 to the Canon Log settings menu.

The numbers Canon publishes, and what they are for

Canon prints a small table at the back of the white paper, and almost nobody reads it.

For Canon Log 3, in 10-bit code values: pure black sits at code 128, an 18% grey card at code 351, a 90% white card at code 577, and the top of the 1600% range at code 1020. Read the code values rather than the percentages, because the percentage depends on which scale you are looking at. Canon quotes those codes as 12.5%, 34.3%, 56.4% and 99.7% on a full-range scale. On the legal-range IRE scale a Sony or Panasonic waveform uses, the same codes read 7.3, 32.8, 58.6 and 109.5. Neither is wrong, and confusing them will convince you a correctly exposed grey card is a tenth of a stop under. IRE is not one unit across manufacturers.

You do not need to memorize that. You need one number: 351. Put an 18% grey card in shot, look at the waveform with no LUT and no conversion applied, and it should read around code 351. If it does, your exposure is where Canon designed it and every conversion downstream will behave. If it reads much lower, you underexposed, and no grading puts back shadow detail that was never recorded cleanly. Canon Log 3 is less forgiving there than most: six stops under middle grey the curve has already fallen to code 134, only six above its own black floor, which is the tightest deep shadow allocation of the seven major log curves.

The table is also how you check a suspicious file. Canon Log 3 and Canon Log share the same black and grey, 128 and 351, but part company at white: 614 against 577. Canon Log 2 differs everywhere, at code 95 for black and 407 for grey. If your software guessed wrong, the grey card is where it shows.

Canon also records these clips as full range rather than video range, and the white paper says the choice cannot be selected. If a step in your workflow assumes video range, your blacks and whites move before you have done anything.

Three routes to a normal picture, and you only need one

Route one is your editor's color management. Modern Premiere, Final Cut and Resolve read the log format out of the file and convert it for you. Least work, and a perfectly good answer for a one camera job. The catch is that it happens silently, so if you then add a Canon LUT as well you have converted twice, and it will look brittle and plastic in the highlights. Premiere applying a LUT to log footage covers what to switch off.

Route two is a color space transform. Add one effect or node, set the input to Canon Log 3 with the matching gamut, set the output to Rec.709, and the software computes it. More clicks, and an exact record of what happened, which matters when you mix cameras. Colors from different brands only line up once every clip is in one shared space, which is the whole of why your cameras don't match.

Route three is Canon's own LUT. Load a .cube file and the picture converts, in anything that can load a LUT, including software with no color management at all.

Do exactly one of these. The most common C-Log3 disaster is doing two, usually route one without realising and route three on purpose. They do not produce identical pictures either, and that is expected rather than a bug: why CST, ACES and LUTs look different explains what each decides for you.

Where Canon's LUTs come from and which one you want

Canon publishes these itself, free. The white paper lists them: 1D LUTs converting Canon Log, Canon Log 2 and Canon Log 3 to Linear, Cineon, BT.709, Wide DR, DCI and PQ, plus 3D LUTs that also convert the color gamut. PQ is offered only for Canon Log 2 and Canon Log 3.

Two of those destinations sound like the same thing and are not. BT.709 is the ordinary television standard. Wide DR is defined in the same document as "A gamma curve equivalent to BT.709, which extends the dynamic range up to 800%." Both are valid, and the Wide DR version holds more highlight information and looks flatter. If you load one, dislike the contrast, and load the other, you have changed which compromise you are living with rather than fixed anything.

You find these on Canon's support site under your camera model. Some packages are still labelled for the Cinema EOS bodies, which convinces R5 owners there is nothing for them. The gamma curve is the gamma curve: a Canon Log 3 to BT.709 LUT converts Canon Log 3. If the same conversion comes at two grid sizes, take the larger, since a bigger grid samples more finely.

Exposure, because it decides how well everything above works

Canon Log 3 delivers approximately 1600% dynamic range at ISO 800 or higher. Setting the ISO manually anywhere between 100 and 640 makes the dynamic range narrower. So on an R5, ISO 800 is a floor for C-Log3 rather than a suggestion. Dropping to ISO 100 for a bright exterior feels responsible and throws away the range you switched to log to get. Use a neutral density filter.

Canon also warns that horizontal banding is more likely on somewhat dark, flat subjects and can appear even at relatively low ISO speeds, around ISO 800 for Canon Log 3. That is the technical description of what people report as grainy log footage: usually underexposure meeting a flat wall or a night sky, made much worse by lifting shadows afterwards.

So expose brighter than feels comfortable, turn on View Assist rather than judging a grey picture by eye, and check the grey card against code 351.

Where the exposure correction sits depends on your route. With Canon's LUT it goes before the LUT, while the clip is still log, because once values pass through the table the damage is baked in. With a color space transform, put the transform first and correct in the working space after it. Either way, exposure comes before the creative look. The same logic in Sony terms is in S-Log3 to Rec.709 conversion.

C-Log2 or C-Log3

Canon Log 2 uses the Cineon digital negative as its basis, places black at code 95, holds a wider straight line region that behaves like film, and extends dynamic range to 6400%. Canon says it "is suited to those workflows where image quality can be enhanced by grading at the postproduction stage." Canon Log 3, meanwhile, "is suited to cases where users want to create the final 'look' of their images by means of simple grading without investing too much time at the post-production stage."

Read those two sentences as a question about your time rather than your skill. If grading is a chore you want over quickly, Canon told you to shoot C-Log3. If you enjoy it and have the codec to support it, C-Log2 gives you more. Canon also recommends Canon Log 2 for ACES workflows, alongside Cinema Gamut and the Neutral color matrix. For most R5 owners the question is academic anyway: Canon's firmware notice describes the R5 menu as offering Canon Log or Canon Log 3.

The order that stops you going in circles

Normalize, balance, look, in that sequence on every clip.

Normalize means one and only one of the three routes above. Balance means exposure and white balance, after the conversion if you used a color space transform and before it if you used a LUT. Look means contrast, saturation, skin and mood, applied last on a picture that is already correct. On a whole timeline that order still applies per shot, which is why the work multiplies so fast: do you have to color grade every clip is about that wall.

Leumos AI, our browser-based grading studio, applies an ACES based input transform for Canon Log, Canon Log 2 and Canon Log 3 on upload, then grades each detected shot toward a reference image and renders the result. It returns finished graded files rather than LUTs or project data, and is in closed beta with a waitlist at leumos.ai. To stay in an editor, grading log footage without DaVinci Resolve covers the options.

Frequently asked questions

What is the fastest correct way to grade C-Log3?

Let your editor's color management identify the clip and convert it, check it is not converted twice, correct exposure and white balance, then grade on top. That is a legitimate finished workflow rather than a shortcut. Reach for a color space transform when you start mixing cameras.

Why does my C-Log3 footage still look flat after applying a LUT?

Either the LUT never loaded, or it is wrong for the curve, or your editor already converted the clip so the LUT is working on an image that is no longer log. Put a grey card frame on the waveform with everything disabled and confirm it reads near code 351 first.

What ISO should I shoot C-Log3 at on an R5?

ISO 800 or higher. Canon's documentation states that Canon Log 3 gives approximately 1600% dynamic range at ISO 800 or higher, and that manually setting anything from ISO 100 to 640 narrows it. Control bright scenes with neutral density filters, not by lowering ISO.

Should I have shot C-Log2 instead?

Only if you were going to spend real time grading. Canon positions Canon Log 2 for workflows where image quality is enhanced by grading in post, and Canon Log 3 for a final look from simple grading. C-Log2 also demands more of your codec and your exposure discipline.

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