color-grade

Color grade (LUTs via ffmpeg)

Grade through LUT files rather than re-deriving filter params each time. Two LUT formats, both native to ffmpeg, no extra deps:

• .cube — a 3D LUT (what colorists ship). Applied with lut3d.
• .png HALD-CLUT — a look baked from a filter chain (below). Applied with haldclut.

The grade command auto-detects by extension.

# Apply a look
uv run video-agent grade apply in.mp4 --lut luts/teal_orange.cube -o out.mp4
uv run video-agent grade apply in.mp4 --lut luts/warm.png        -o out.mp4   # HALD

"Make a few looks and let me choose"

The best grading UX: render the SAME frame through several candidate looks into one labelled contact sheet, show it, let the user pick — then apply the winner to the whole video.

uv run video-agent grade preview in.mp4 --at 45.0 \
    --lut none --lut luts/warm.png --lut luts/teal_orange.cube --lut luts/punchy.png \
    -o looks.png
# read looks.png → user picks → grade apply with that one

none = the ungraded original (always include it for reference). Pick a frame (--at) with skin tones + a bright and a dark area so the grade's effect is visible.

Bake a look into a reusable LUT

Author a look as a color-filter chain, then bake it into a HALD LUT once so it's reusable and fast to apply:

uv run video-agent grade gen-lut \
    --eq "curves=r='0/0 .5/.55 1/1':b='0/.03 1/.97',colorbalance=rs=.05:bs=-.05" \
    -o luts/warm.png

This runs an identity HALD-CLUT through the chain → a .png LUT. Use available filters only — this ffmpeg is LGPL, so no eq (and no drawtext). Grade with: curves (the workhorse — per-channel tone curves), colorbalance (shadows/mids/highlights RGB), colorchannelmixer (channel mixing / saturation), lut1d. Quick starting points:

• warm: colorbalance=rs=.04:rm=.03:bs=-.04:bm=-.03
• teal-orange: colorbalance=rh=.06:bs=.08 + lift shadows blue, push highlights warm
• punchy: curves=all='0/0 .25/.18 .75/.82 1/1' (S-curve contrast) + light saturation via colorchannelmixer
• desaturate/filmic: colorchannelmixer toward grey, or curves to lift blacks

Where grading sits in a pipeline

• Grade at the final encode, after cuts/reframe, before captions/overlays (so burned text keeps its intended color). In an edl-edit job, set "grade": "luts/x.png" in the EDL and it's applied to the whole cut in the same pass.
• Grading helps most on flat/log/prosumer footage; typical Rec.709 screen-recordings and webcams need only a gentle lift. Don't over-grade — a subtle look beats a heavy filter.

Gotchas

• .cube vs HALD: external colorist LUTs are usually .cube (→lut3d); looks you bake here are .png HALD (→haldclut). The command handles both; just keep the extension honest.
• HALD level: gen-lut defaults to level 8 (a 64³ grid) — plenty for smooth grades; raising it makes a bigger file, rarely needed.
• Grade once, reuse: commit your luts/*.png (or .cube) so the look is plain-text/ data and re-applies identically across clips and re-renders.