A .cube file is the universal format for video color LUTs (Look-Up Tables). If you have ever downloaded a LUT pack or a color grade from a creator online, it almost certainly arrived as a .cube file. This guide explains what is actually inside one, what the size numbers mean (17, 33, 65), and how to use one on iPhone.
What "LUT" means
LUT stands for Look-Up Table. In video color grading, a LUT is a list of mappings from an input color to an output color. The video player reads every pixel, looks up its color in the table, and replaces it with the mapped color. Applied uniformly across every frame, a LUT gives you a consistent color grade.
LUTs come in two broad flavors:
- 1D LUTs. Map each color channel (red, green, blue) independently. Mostly used for simple gamma and contrast adjustments. Less common today.
- 3D LUTs.Map a three-dimensional color cube (RGB triplet in, RGB triplet out). These are what people mean when they say "a LUT" today. They can express any color transformation, including creative film looks.
The .cube format supports both. Most files you will encounter are 3D.
What is inside a .cube file
A .cube file is plain text. You can open it in any text editor and read it. The structure looks like this:
TITLE "My Film Look" LUT_3D_SIZE 33 DOMAIN_MIN 0.0 0.0 0.0 DOMAIN_MAX 1.0 1.0 1.0 # A long list of RGB triplets, one per line. # Each row is an output color, mapped from a position in a 3D color cube. 0.000000 0.000000 0.000000 0.031250 0.029167 0.026389 0.062500 0.058333 0.052778 ...thousands more lines... 1.000000 1.000000 1.000000
The first few lines are metadata: a title, the size of the 3D color cube, and the input range. The bulk of the file is a long list of RGB triplets — every possible input color and what it should become.
The size number: what 17, 33, and 65 mean
The LUT_3D_SIZE line tells you the resolution of the color cube. The number is the size of one edge — so a 33-cube has 33×33×33 = 35,937 entries, and a 65-cube has 65×65×65 = 274,625 entries.
Common sizes and what they mean:
- 17-cube. 4,913 entries. Smallest practical size. Fine for camera transforms and simple looks. Tiny file size, fast to load, very slightly less precise than larger sizes.
- 33-cube. 35,937 entries. The default for most LUT packs. The size most creators ship and the size most editors default to. Good balance of precision and performance.
- 65-cube. 274,625 entries. Used for high-end film emulations where subtle color differences matter. Larger file, slower to parse, no visible quality difference for most footage.
For most creators, 33 is the sweet spot. The precision difference between 33 and 65 is invisible on consumer displays, and 65-cube files are roughly 8× the size of 33.
File size and limits
Because they are plain text, .cube files are tiny. A 33-cube is usually under 1 MB; a 65-cube tops out around 8 MB. The iPhone-native editor ReelClip accepts .cube files up to a reasonable size limit (its parser rejects files that are too large to safely load) and supports the standard 17/33/65 sizes plus a few common variants.
If you ever see a .cube file fail to load, the most common cause is an unsupported combined-table header (some editors write 1D + 3D LUTs in one file). The fix is to export just the 3D table from whichever tool created it.
How to import and use a .cube LUT on iPhone
Step 1: Save the .cube file to your iPhone
Unzip the LUT pack if needed. Save the .cube file somewhere iOS can read: Files (on-device or iCloud Drive), Dropbox, Google Drive. The exact location does not matter — ReelClip reads it from any folder the Files picker can reach.
Step 2: Open the video in ReelClip
Import the clip you want to grade. If the clip is log footage (DJI D-Log, Apple Log, HLG), set the camera color profile first so ReelClip applies the right camera transform.
Step 3: Import the LUT
In the Look panel, tap Import LUT and pick the .cube file. ReelClip validates the header, parses the color entries, and adds it to your on-device LUT library. The file stays on your phone.
Step 4: Apply and adjust
Select the LUT and adjust the strength slider. Stack a creative look on top of the camera transform for stylized grades, or apply just the camera transform alone for accurate color reproduction.
Step 5: Export
Save the graded clip to Photos. The output is a standard Rec.709 video file with the LUT baked in.
Common .cube gotchas
- 1D and 3D combined tables. Some editors write both into a single .cube file. ReelClip rejects these and asks you to export just the 3D portion.
- Wrong domain range. Most LUTs use 0.0–1.0 domain. Some older camera LUTs use -0.1 to 1.1 (extended range for highlights). Both work, but the editor needs to apply the right range.
- Truncated files. If the file was cut off during download, the editor cannot fill in the missing entries. Re-download.
- Unsupported sizes. Anything outside 2–65 (ReelClip's supported range) will be rejected. Convert to 33 if you have an unusual size.
What to do next
For the practical application side — what LUTs to use, how to stack them, and the exact settings for DJI Osmo Pocket footage — see DJI Osmo Pocket 3 LUTs and how to apply a .cube LUT on iPhone.