Convert Log Footage to Rec.709

A modern sensor can capture twelve or more stops between the deepest shadow and the brightest highlight that still hold detail. A normal video file and the screen showing it are designed around far less. Log recording solves the mismatch by spacing its code values roughly evenly per stop, so shadows and highlights both get a fair share of the file. The price is that nothing in the file is encoded for display: mid-grey sits higher than usual, blacks are lifted, whites are pulled down, and the picture looks low in contrast.

Most log profiles also record in a wide gamut, such as S-Gamut3 or V-Gamut, whose red, green and blue primaries lie well outside those of standard video. Shown on an ordinary screen without conversion, those primaries are read as if they were Rec.709 ones, so every colour looks pale. That is two problems, tone and gamut, which is why a proper conversion has to deal with both.

What the conversion does

For each profile, the tool undoes the log curve using the formula the camera maker published, turning the code values back into scene light. It then converts the wide-gamut primaries to Rec.709 primaries with a colour matrix, and finally applies a neutral display rendering: a tone curve with a soft roll-off into the highlights, followed by standard BT.709 encoding. That last stage is our own design. It is not the manufacturer’s LUT, so the result will be close to, but not identical with, a maker’s look such as Sony’s s709 or Canon 709. If you need that exact look, import the maker’s LUT instead.

• Sony: S-Log3 / S-Gamut3.Cine and S-Log3 / S-Gamut3
• Panasonic LUMIX: V-Log / V-Gamut
• Canon: Canon Log 3 / Cinema Gamut, Canon Log 2 / Cinema Gamut and Canon Log / Cinema Gamut
• Fujifilm: F-Log / F-Gamut and F-Log2 / F-Gamut
• ARRI: LogC3 (EI 800) / Wide Gamut 3
• Apple: Apple Log / Rec.2020
• Nikon: N-Log / Rec.2020
• DJI: D-Log / D-Gamut

Not built in: use the maker’s LUT

DJI D-Log M, GoPro Log, Samsung Log and Apple Log 2 aren’t in the list, because their curves and gamuts aren’t published in a form we can implement faithfully. Choosing a near neighbour, such as D-Log for D-Log M footage, gives colours that look plausible but are wrong. Instead, download the maker’s conversion LUT, choose Import LUT on the LUT tab, and set Apply LUT to Before the grade, leaving Footage on Standard video (Rec.709).

Official pages, linked rather than mirrored: Sony LUT library, Panasonic V-Log, Fujifilm 3D LUTs, DJI LUTs, GoPro Log LUTs and Nikon N-Log 3D LUT. Canon publishes its LUTs on each camera’s support download page.

• Record in 10-bit whenever the camera offers it. Log spreads tones thinly across the code values, and 8-bit log tends to band in skies and walls once contrast is restored.
• Convert before anything else. Set Footage first, then correct and grade; a look applied to unconverted log never looks right.
• Convert once. If the camera or a phone app has already burned a LUT into the file, it is no longer log, so leave Footage on Standard video (Rec.709).
• Check skin on the Vectorscope after converting. If faces drift off the skin tone line, adjust Temperature and Tint rather than piling a look on top.
• Grade a whole shoot consistently: finish one clip, choose Copy grade (Shift+C), open the next and choose Paste grade (Shift+V), then check that Footage still matches the profile that clip was shot in.