Apply 3D color lookup tables (LUTs) to images for cinematic color grading.
A 3D LUT is a cube of numbers, not a look you can see. The .cube file - the format shared by DaVinci Resolve, Photoshop, and After Effects - holds thousands of input-to-output RGB mappings, and this tool turns that table into a graded image: upload a photo and a .cube, and every pixel is looked up in the cube and re-rendered. The catch users hit first: a LUT never says which color space it was built for. Feed a Rec.709 grade to log footage and you get a double grade, and the tool has no way to warn you.
A concrete input and expected output from the current implementation.
Input
A .cube file (LUT_3D_SIZE 2) whose corners implement out = 0.9 x in + 0.05 per channel: TITLE "Lift and slight contrast" LUT_3D_SIZE 2 0.05 0.05 0.05 0.05 0.05 0.95 0.05 0.95 0.05 0.05 0.95 0.95 0.95 0.05 0.05 0.95 0.05 0.95 0.95 0.95 0.05 0.95 0.95 0.95
Expected output
The photo re-rendered with the grade applied. For an input pixel of (0.2, 0.4, 0.6) the tool computes (0.23, 0.41, 0.59); over the whole image the grade reads as lifted shadows and slightly compressed highlights.
A size-2 cube stores only its eight corners, and trilinear interpolation reproduces any affine per-channel grade exactly, so the sample maps by the formula with no interpolation error: 0.9 x 0.6 + 0.05 = 0.59 for blue, and likewise for red and green. The grade lifts black to 0.05 and lowers white to 0.95, a mild film-style fade.
A .cube file is plain text: an optional TITLE, then LUT_3D_SIZE N, then N cubed data rows, each holding the output red, green, and blue for one position in the table. Rows are ordered with blue changing fastest, so the first row is the R=G=B=0 corner and the last is R=G=B=1. Size 17 means 4,913 rows; size 33 means 35,937; the row count is a quick validity check.
A pixel's RGB values address a point inside the cube, and its graded color is blended from the surrounding samples; trilinear interpolation over the eight nearest corners is the standard scheme, and denser tables - 33 or 65 samples per side - track a grade more smoothly than sparse ones. Output values outside the renderable 0-1 range are clamped, so LUTs built for log or HDR input lose range on normal images.
Vendors build previews with their own sample image, exposure, and input color space, then apply the LUT on top. Here your file's pixel values go into the table directly. If your image sits in a different space than the one the LUT expects - sRGB instead of Rec.709, say - the look shifts. Matching the input space first usually closes most of the gap.
No. It applies the .cube tables you bring to still images; it neither builds LUTs nor processes footage. To create a LUT, export one from a grading tool - DaVinci Resolve exports .cube natively - then use it here for stills and in your editor for video.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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