Converter !!hot!!: Xmp To Cube

Technical Report: XMP to CUBE Color Conversion Utility Report ID: ICC-CVT-0426 Date: April 18, 2026 Author: Color Science Division 1. Executive Summary This report details the design and implementation of a converter that translates Adobe Camera Raw (XMP) look-up table data into Cube LUT (CUBE) format. The converter addresses the interoperability gap between Adobe’s parametric color adjustment engine (used in Lightroom/ACR) and 3D LUT-based color pipelines (e.g., DaVinci Resolve, Unreal Engine, OCIO). The core challenge lies in transforming XMP’s parametric Look table (typically 32×32×32 or 64×64×64) into a static, vendor-neutral CUBE file. 2. Introduction 2.1 Background

XMP (Extensible Metadata Platform): Contains color adjustment parameters (exposure, contrast, saturation, HSL, tone curve) and optionally an embedded 3D Look table for creative profiles. CUBE: A plain-text 3D LUT format defined by Adobe after acquiring IRIDAS. Each line represents a mapped RGB triplet for a specific input grid point.

2.2 Problem Statement No native tool directly converts an XMP profile (containing a Look table) to a CUBE file without intermediate rendering (e.g., applying the XMP to a reference image and extracting the transform). This converter solves that by directly parsing, interpolating, and exporting the 3D mapping data. 3. Architecture & Workflow The converter operates in four stages: XMP File → XML Parser → 3D LUT Extractor/Reconstructor → CUBE Writer

3.1 XMP Parsing

XMP is XML-based. The tool extracts the <crs:LookTable> element. Key tags:

crs:LookTableData – base64-encoded 3D grid (if embedded) crs:LookTableDimensions – e.g., 32 32 32 crs:LookTableInputMin/Max – typically 0 0 0 to 1 1 1

3.2 3D LUT Reconstruction

If an explicit LookTableData exists, it is decoded and directly used. If only parametric adjustments exist (no embedded LUT), the converter must render a neutral 3D lattice through the XMP’s color model. This is optional and marked as an advanced mode.

3.3 CUBE Generation The CUBE format is written as per the IRIDAS v1.0 specification: TITLE "Converted from XMP" LUT_3D_SIZE 32 DOMAIN_MIN 0.0 0.0 0.0 DOMAIN_MAX 1.0 1.0 1.0 LUT_3D_DATA R G B ...

4. Algorithm for Grid Mapping For a grid size ( N ), the input RGB coordinates are: [ r = \frac{i}{N-1},\quad g = \frac{j}{N-1},\quad b = \frac{k}{N-1} ] where ( i,j,k \in [0, N-1] ). Each input RGB vector is transformed by the XMP’s internal color pipeline (including exposure, curve, HSL, calibration). The resulting RGB is written to the CUBE. 4.1 Interpolation Note If the XMP Look table is smaller than desired CUBE size (e.g., XMP has 32³ → output 64³), trilinear interpolation is applied. 5. Implementation Examples 5.1 Python Prototype (Pseudocode) import xml.etree.ElementTree as ET import base64 import struct def xmp_to_cube(xmp_path, cube_path, out_size=64): tree = ET.parse(xmp_path) root = tree.getroot() ns = {'crs': 'http://ns.adobe.com/camera-raw-settings/1.0/'} # Get embedded LUT or simulate from params dim_elem = root.find('.//crs:LookTableDimensions', ns) if dim_elem is not None: dims = list(map(int, dim_elem.text.split())) data_b64 = root.find('.//crs:LookTableData', ns).text raw = base64.b64decode(data_b64) # Parse raw float32 data lut = [struct.unpack('f', raw[i:i+4])[0] for i in range(0, len(raw), 4)] # Reshape to (dims[0], dims[1], dims[2], 3) xmp to cube converter

# Write CUBE file with open(cube_path, 'w') as f: f.write(f"TITLE Converted from {xmp_path}\n") f.write(f"LUT_3D_SIZE {out_size}\n") f.write("DOMAIN_MIN 0 0 0\nDOMAIN_MAX 1 1 1\nLUT_3D_DATA\n") # Write out interpolated RGB values...

5.2 Command-Line Tool Usage $ xmp2cube --input profile.xmp --output profile.cube --size 64 --interp trilinear