Lut 3D

Przekształca wartości RGB za pomocą pliku 3D LUT.

3D LUT to trójwymiarowa tablica, używana do konwersji zadanej wartości RGB do innej. Używana jest do symulowania kliszy filmowej oraz korekcji koloru.

This module accepts .cube, .3dl and .png (haldclut) files. Uncompressed 3D LUT data is not saved in the database or the XMP file, but is instead saved to the 3D LUT file path inside the 3D LUT root folder. It is therefore important to back up your 3D LUT folder properly – sharing an image with its XMP is pointless if the recipient doesn’t also have the same 3D LUT file in their own 3D LUT folder.

The compressed G’MIC format .gmz is no longer supported. If you have .gmz files, see Converting .gmz files below.

Uwaga: moduł obcina wszystkie wartości spoza zakresu [0,1]. Przemyśl redukcję zakresu wejściowego przed zastosowaniem modułu.

Usage

LUTs are most commonly used in Ansel for color grading or film look simulation. For this reason, by default, the module is placed after the filmic module in the pixelpipe and should be applied to a neutral image (without first applying a specific look). While you can find hundreds of free LUTs on the internet, you should note that not all of them are compatible with the Ansel environment and workflow – incompatible LUTs will not produce the advertised look. To limit the risk, a color grading LUT should have been created to work with one of the available “application color spaces” (see below), for both the input and the output of the module.

Logarytmiczne tablice LUT aparatów (takie jak F-log lub S-Log3) różnią się od tabel LUT z gradacją kolorów i symulacją wyglądu filmu i mają na celu konwersję nieprzetworzonych danych rejestru kamery na coś (nieprzetworzone dane liniowe lub inną przestrzeń kolorów), które Ansel jest w stanie zrozumieć. W takim przypadku moduł lut 3D należy ręcznie umieścić między modułami demozaikowania i profilu koloru wejściowego. Po wykonaniu tej czynności nie można już wybrać „przestrzeni kolorów aplikacji”. „Profil wejściowy” modułu wejściowego profilu kolorów powinien być zgodny z wyjściem LUT. Pamiętaj, że ten przypadek użycia nie został jeszcze przetestowany.

Module controls

file selection

Choose the 3D LUT file to use. File selection is inactive if the 3D LUT root folder has not been defined in preferences > processing.

przestrzeń kolorów

Tablica 3D LUT jest definiowana w odniesieniu do określonej przestrzeni kolorów. Wybierz przestrzeń kolorów, dla której zbudowano wybrany plik 3D LUT. Pliki kostek są zwykle powiązane z REC.709, podczas gdy większość innych jest związana z sRGB.

metoda interpolacji

Definiuje sposób obliczania kolorów wyjściowych, gdy kolory wejściowe nie znajdują się dokładnie w węźle kostki RGB, opisanej przez tablicę 3D LUT. Dostępne są trzy metody interpolacji: czworościenna (domyślna), trójliniowa i piramidalna. Zwykle nie zobaczysz żadnej różnicy między metodami interpolacji, z wyjątkiem LUT o mniejszych rozmiarach.

Converting .gmz files

What changed, and why

Ansel used to read .gmz, G’MIC’s own compressed LUT container. Support for it has been removed, along with the G’MIC dependency itself.

The reason is proportion. Ansel called exactly three functions from G’MIC — read a .gmz, decompress its keypoints, cache the result — and linking those three functions meant linking all of G’MIC: a 7.4 MB shared library that in turn pulls in around fifty more, among them libcurl, OpenSSL, libssh, LDAP, Kerberos and SASL — a complete HTTP and TLS stack, in a photo editor — plus an X11 display stack and G’MIC’s own private copies of libpng, libjpeg, libtiff, OpenEXR, WebP and FFTW, duplicating decoders Ansel already links directly. G’MIC also required Ansel to raise the stack size of every thread it creates to 2 MiB, and it published its own OpenMP thread count process-wide, which silently overrode Ansel’s “CPU cores” preference for anyone who set it.

That was the cost. The benefit, measured over 61 days of anonymous usage statistics: the whole 3D LUT module accounts for 0.2 % of module activations, and .gmz is only a fraction of that — most people who use LUTs use .cube.

Nor is .gmz merely a container that could have been parsed in a few lines. Its keypoints are reconstructed either by a dense radial-basis-function solve or by a multiscale diffusion PDE, both written in G’MIC’s own scripting language. Reimplementing and then maintaining two numerical solvers in Ansel, forever, to read a format that ships alongside a .cube equivalent, is not a trade worth making.

So the format is deprecated, and converting is a one-off.

The easy way: download the .cube version

Most .gmz files in circulation are the G’MIC film-emulation CLUT collections, and the same collections are published as .cube. Before converting anything, check whether the pack you use offers a .cube download — for most people that is the whole procedure.

Converting with the G’MIC command line

G’MIC’s own command-line tool reads .gmz and writes .cube. Install it:

A .gmz can hold a single LUT or a whole library of them, each with a name. This command converts every LUT in the file, one .cube per LUT, keeping the original names:

1mkdir -p converted
2gmic input.gmz foreach { nm={n} decompress_clut 33,33,33 output_cube converted/$nm.cube }

Reading it left to right: load the .gmz; for each LUT it contains, remember the LUT’s name, decompress its keypoints into a 33×33×33 cube, and write that cube out under the remembered name. Capturing {n} before decompress_clut matters — the decompression step replaces the image name with an internal expression, so a naive output_cube {n}.cube produces files called things like (256;0^256;255^256;1).cube.

33,33,33 is the output resolution, and 33 is the conventional size for a .cube. You can ask for more (65,65,65) at the cost of a much larger file and a slower conversion; the keypoints hold no more detail either way, so this only changes how finely the reconstruction is sampled.

For a single-LUT file where you do not care about the name, the short form is enough:

1gmic input.gmz decompress_clut 33,33,33 output_cube output.cube

Decompression is not instant — it is solving a scattered-data interpolation problem — so expect a few seconds per LUT.

Converting with the GIMP plugin

If you would rather not use a terminal, the G’MIC-Qt plugin for GIMP can do it: open the .gmz, and in the CLUT filters set the output mode to Save CLUT as .cube or .png File.

Afterwards, in Ansel

Put the converted .cube files in your 3D LUT root folder (set in preferences > processing), then select the LUT again in the module. The result is identical: the .cube holds the same reconstructed LUT that Ansel used to compute from the .gmz on every load, so this is also slightly faster to open.

Existing edits that referenced a .gmz will not be silently altered. Ansel detects them and applies no LUT at all, rather than guessing; in the darkroom you get a dialog naming the file, and elsewhere a line in the log identifying the image. Those edits need the LUT re-selected once, pointing at the converted .cube.

This applies as well to edits made with a much older version, which stored the compressed LUT data inside the edit rather than referencing a file. Ansel recognises those too, and the remedy is the same.