Apply a .cube LUT to a photo online

What applying a LUT in Lightframes means

A LUT (look-up table) is a file that maps every input colour to an output colour, and applying one gives a photo a ready-made colour grade in one step. Lightframes reads 3D LUTs in the common .cube format, the same files often sold or shared as film emulations and cinematic looks, and lets you apply them to still photos, including camera RAW files. It is for photographers who already own LUTs, video creators who want matching stills, and anyone who wants a consistent grade across a set. The editor is free, open source and runs in the browser.

How it works, and why it stays on your device

The .cube file is read and applied by the editor in your browser, and neither the LUT nor your photos are uploaded. When you import a LUT:

1. Lightframes parses the text file, checks it is a 3D LUT and that the number of samples matches LUT_3D_SIZE, and rescales values if the file uses a custom DOMAIN_MIN / DOMAIN_MAX.
2. It saves the LUT as a preset in your browser’s IndexedDB storage. That storage has room for large LUTs; a 65-point cube holds over 270,000 colour samples.
3. When applied, every pixel is looked up in the cube with trilinear interpolation. This happens after your other edits and local masks, and the Intensity slider mixes the result with the un-graded image.

Edits are non-destructive. The LUT is stored as a setting on the photo, and the original file is never changed.

Supported LUT files

Property	Supported
File type	.cube (plain text)
Dimensions	3D only (LUT_3D_SIZE)
Cube size	2 to 128 points per axis
Domain	DOMAIN_MIN / DOMAIN_MAX, normalised automatically
Title	Read from TITLE "…", otherwise the file name
Comments	Lines starting with # or // are ignored
Not supported	1D LUTs (LUT_1D_SIZE), .3dl, .look, .csp and other formats

Photos can be JPEG, PNG or any supported camera RAW. Exports can be JPEG, PNG or WebP.

Using LUTs together with your own edits

Because the LUT sits at the end of the pipeline, the sliders work as input controls for it:

• Exposure and white balance first. Most creative LUTs assume a correctly exposed, neutral image, so fix those before judging the look.
• Save a combined look. When the sliders and LUT work well together, type a name in Save current edits as… and save. The new preset contains both your adjustments and the LUT.
• Apply to many photos. Select photos in the filmstrip and click the preset, or copy the edits and paste only the Look (LUT) group. See the batch photo editor.
• Manage LUT presets like any other. Delete with ×, download one as JSON, or save all of them with Backup. More in photo presets.

Tips for better results

• Pick LUTs made for standard (Rec.709 / sRGB) images. LUTs built to convert camera log footage expect a flat log input and will look far too contrasty on a normal photo.
• Start at 100% intensity to see what the LUT does, then pull it back. Many looks sit well between 50% and 80%.
• If a LUT clips highlights, lower Highlights or Whites before it rather than reducing intensity.
• Check skin tones with the before/after view (\) when using strong teal-and-orange grades.

Limitations

• Only 3D .cube files are accepted. Convert other formats to .cube first.
• One LUT per photo. Applying a second LUT preset replaces the first instead of stacking.
• LUTs are applied to 8-bit display values after development, not to the RAW’s linear data.
• The editor can’t export a .cube; LUT presets are exported as Lightframes JSON, which includes the LUT data.
• Applying an imported LUT preset sets the tone and colour sliders to neutral, so apply it before fine-tuning, not after.

For more about how the editor works, see the FAQ.