lovell/sharp

Feature request: expose libvips maplut operation to map pixel values (for e.g. colour grading)

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#1,441 opened on Oct 30, 2018

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enhancementhelp wanted

Description

I'm interested in being able to apply 3D LUTs to images on the fly, eg. .cube files. I think vips_maplut() is the right function under the hood for this, perhaps I'll need to figure out how to generate LUT images from those files first though.

I've been trying to use some node libraries to do this, extracting the pixels as an ndarray, applying the LUT, then saving the modified pixels back to an image buffer but it's super slow and error prone (truncated image data etc).

If it's not something that makes sense for sharp no worries, hopefully I can find info on transforming an image as a readableStream assuming that's doable :)

Contributor guide

Tech stack
javascriptnodejs
Domain
backendapi
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Node.jslibvipsC++sharp internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Examine the libvips documentation for the vips maplut function and how it maps pixel values using LUTs. Inspect sharp's existing C++ bindings in the src/ directory to understand the pattern for wrapping libvips operations. Review the issue comments for any design discussions or suggestions from maintainers. Consider how to parse .cube files and generate the appropriate LUT image format required by vips maplut.