LUT Tuner Makes LUTs Tunable in Resolve

For those who don’t know the tool: Cutpoint Labs makes focused Mac and iPhone utilities for editorial and finishing. LUT Tuner sits between LUT preparation and grading: it edits and inspects .cube 3D LUTs, then can turn the edited result into an adjustable DCTL approximation for DaVinci Resolve.

A LUT with knobs attached

LUT Tuner has acquired a more interesting trick than another LUT export button. Cutpoint Labs can now take an edited .cube 3D LUT and create a tunable DCTL approximation for DaVinci Resolve. The point is not simply changing file extensions. A conventional LUT is baked. LUT Tuner’s generated DCTL exposes controls for tone strength, colour strength, exposure, input contrast, contrast pivot, range handling, Invert and Global Blend inside Resolve. That makes the result useful downstream. A colourist can start with the character of an existing LUT but retain defined controls once the transform enters the node tree. The application can export the edited .cube, the DCTL, or both. Keeping both is probably the sensible production option: one remains the conventional LUT deliverable, the other is an adjustable derivative.

Cutpoint Labs explicitly says LUT Tuner is not a full grading application or video editor. Good. Its value is narrower: take an existing LUT, inspect it, make targeted changes, test those changes against real material, and either export the revised LUT or turn it into something more adjustable for Resolve. That can eliminate the slightly awkward workflow where a LUT needs one specific correction, but opening a complete grading project feels rather like starting Flame to rename a file.

Approximation, not alchemy

Cutpoint Labs is clear about what happens under the hood, at least at the workflow level. LUT Tuner does not hide the original 3D LUT inside a DCTL wrapper. It approximates the edited LUT with adjustable DCTL code. Consequently, the DCTL is not (!) guaranteed to reproduce the table exactly.

To make that difference inspectable rather than philosophical, LUT Tuner previews the fitted DCTL before export and reports mean, p95 and maximum RMSE values. Operators can therefore judge the approximation visually on images or patterns and get numerical error measurements alongside it. There is no published value that magically means “broadcast safe”, “feature safe” or even “probably fine”. The metrics are evaluation tools, not certification. The acceptable error depends on the transform, imagery and tolerances of the job. Still, reporting the error beats exporting a mysterious approximation and hoping nobody notices during the attended grade.

Colour assumptions included

When generating the DCTL, LUT Tuner lets the user define the intended input and output colour-space and transfer-function assumptions. That does not make the application a replacement for Resolve colour management. It defines the expected context of the generated transform. Project colour management, node placement and the rest of the grading pipeline remain somebody else’s problem, as tradition demands.

For colourists, DITs and finishing artists who regularly inherit LUTs that are almost right, “almost right, but adjustable” may be considerably more useful than another folder containing final_final_v7_nowrealllyfinal.cube.

More range, fewer miracles

The DCTL can also operate differently from the bounded LUT it approximates. Cutpoint Labs provides Match LUT and Preserve Extended Range handling. With Preserve Extended Range selected, the DCTL can retain image information beyond the finite range represented by a conventional LUT. That can be useful in log, HDR and wide-gamut pipelines where values outside the LUT’s nominal domain may still be needed by later operations.

This should not be translated into “DCTL prevents clipping”. It does not protect the image from everything elsewhere in the node tree. The claim is: the generated transform can preserve extended-range data instead of reproducing the bounded behaviour of the LUT. Match LUT is there when matching that bounded response is precisely the point.

Invert first or enjoy debugging

LUT Tuner’s inverse workflow is equally specific. Cutpoint Labs instructs Resolve users to place two copies of the generated DCTL on consecutive nodes. Enable Invert on the first, upstream node, then place the normal forward DCTL on the following node.

Order matters.

The first node removes the original or default transform. The second reapplies the adjustable look. Putting the inverse after the forward transform defeats the intended processing order. Adjustment parameters also need to remain matched between the pair. The developer specifically documents exposure, input contrast, contrast pivot, tone strength, tone neutralisation and colour strength as settings that should stay aligned, unless they are simply left at their defaults. And no, Invert is not an RGB time machine. Cutpoint Labs warns that once a forward transform has compressed or clipped information, its fitted inverse cannot accurately reconstruct what has already disappeared.

The LUT editor underneath

Before any DCTL fitting happens, LUT Tuner remains a direct .cube editor. It opens and exports standard .cube 3D LUTs and displays their response curves. RGB points can be adjusted together or by individual red, green and blue channels. Lasso selection, radius-based influence, keyboard nudging, undo, redo and reset provide the editing controls.

The application also lets users compare the current edit with the original LUT or bypass LUT processing altogether. Preview interpolation defaults to tetrahedral, with trilinear available for comparison. That is useful when comparing behaviour across applications because identical LUT data does not necessarily produce identical pictures when two systems interpolate the table differently. LUT resizing and resampling are available as well, with export using the currently sampled LUT size.

Bring pictures, not just ramps

The preview system accepts generated patterns, still images and video, so operators do not have to judge every curve adjustment from a graph. Documented still formats include PNG, JPEG, TIFF, EXR, DPX and HEIC. Video preview handles compatible .mov, .mp4 and .mxf media, with Cutpoint Labs listing ProRes, DNxHD/DNxHR, H.264, HEVC, MPEG-2, AV1, VP9, CineForm, JPEG 2000 and uncompressed video among commonly compatible codecs. Container combinations still matter, and ProRes RAW is explicitly unsupported.

Video can be paused and stepped frame by frame. While paused, the picker reports source and processed RGB values. Those media formats are preview inputs. LUT Tuner is not documenting EXR, MXF or ProRes media export. Its production outputs here are .cube LUTs and Resolve DCTLs.

Local Mac plumbing

LUT files, preview media and adjustment work are processed locally on the Mac during normal operation. The current Mac App Store listing requires macOS 12.0 or later and an Apple M1 chip or newer. Intel Macs are therefore outside the documented hardware requirement. The U.S. Mac App Store currently lists LUT Tuner at $24.99.

https://apps.apple.com/us/app/lut-tuner/id6785024507?mt=12
https://cutpointlabs.com/lut-tuner/