Why S-Log3 looks wrong straight off the card
It is supposed to. S-Log3 is a recording curve, not a look: it spreads the sensor's range across the file so highlights survive, and the price is an image that arrives grey, low in contrast and slightly green. Sony's own guidance is to shoot it at the camera's higher base ISO and expose to the right, which makes the flatness worse on the monitor and better in the file.
Converting means mapping that curve back to Rec.709 — the standard ordinary video is delivered in. A conversion LUT is the file that does the mapping.
| Term | What it is |
|---|---|
| S-Log3 | Sony's flat recording gamma |
| S-Gamut3.Cine | The colour space it is usually paired with |
| Rec.709 | The standard delivered video uses |
| Conversion LUT | The file that maps one to the other |
Pay attention to the gamut, not just the gamma. A LUT built for S-Log3/S-Gamut3.Cine applied to footage shot in S-Log3/S-Gamut3 will be close enough to fool you on a phone and wrong on a calibrated screen. Both strings are in the camera menu; the LUT filename usually carries them too.
Which LUT
Sony publishes conversion LUTs for its cameras, and they are the right place to start. The usual complaint is that the official conversion runs dark and contrasty — it is built to be safe for broadcast rather than flattering — and a great many people end up on a third-party conversion for that reason.
Neither choice is wrong. What matters is that the same one is used across the whole shoot, because two conversions in one edit is a colour problem you will spend an evening on later.
Converting one clip
Every editor does this, and none of them takes long:
- DaVinci Resolve — a LUT on a node in the colour page, or the input LUT in clip attributes.
- Premiere Pro — the Input LUT slot in Lumetri.
- Final Cut Pro — a custom LUT effect on the clip.
The mechanics are covered properly in applying a LUT in DaVinci Resolve and the Premiere workflow.
Converting forty clips
This is the part that is actually the job, and where every one of those tools starts asking for a project.
| Route | What it costs |
|---|---|
| Resolve | Project, timeline, clips selected, render queue configured |
| Premiere | Interpret Footage per bin, then a batch export that fights back |
| ffmpeg | A shell loop, no preview, and you find out afterwards |
| Clip by clip | A minute each, times forty |
None of them is hard. All of them are ceremony around a decision you already made when you picked the LUT.
The clip that needs less
The reason batch conversion has a reputation for going wrong is that the same conversion does not suit every clip on the card. Interiors shot at base ISO take it cleanly. The shot into the window at the end of the day takes it and loses the sky.
In an editor that is a per-clip opacity on the node. In ffmpeg it is nothing at
all — lut3d has no opacity — so it becomes a filtergraph you write by hand:
[0:v]split[base][grade];
[grade]lut3d=file=slog3_rec709.cube[graded];
[base][graded]blend=all_mode=normal:all_opacity=0.75That is a reasonable thing for a tool to do and an unreasonable thing to ask a person to type when what they wanted was "a bit less on this one".
How BatchTone handles it
Drop the folder in, pick the conversion, and every clip takes it. A frame is pulled from each clip and previewed with the LUT applied, so the judgement happens on your own footage. The clips that need less get a slider; the rest stay where they are.
- Audio is copied across untouched rather than re-encoded.
- Encoding uses the Mac's own hardware encoder, so a card is not an overnight job.
- Originals are never written to.
- 10-bit HEVC from the newer bodies is read directly.
Same job on the drone side, same tool — the D-Log conversion is the same shape of problem with a different file. There is a seven-day trial, which is the only honest way to find out whether it reads what your camera writes.
Common questions
Does converting S-Log3 lose quality?
The conversion is a colour mapping and costs nothing in itself. What costs quality is re-encoding, so export once at a sensible bitrate rather than converting, editing and exporting again.
Should I convert before editing or after?
Before, if the whole shoot needs the same look and the client wants files rather than an edit. After, if only a handful of clips make the cut — converting material nobody will watch is wasted machine time.
Can I grade on top of the conversion?
Yes, and that is the normal order: conversion first to get to Rec.709, creative look second. Two LUTs stacked in the wrong order is one of the more common ways footage ends up unrecoverable.
What about S-Log2 or older bodies?
Same idea, different file. Use the conversion built for the gamma and gamut the camera actually recorded — the what a LUT is piece has the short version of why mixing them misbehaves.