jimp-dev/jimp

Question about reading 24-bit bmp files

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#1,026 opened on Jul 7, 2021

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bughelp wantedreproduction needed

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Description

I have a 24-bit bmp file that I want to get the rgb values for the pixels. I'm trying to use Jimp. If I open the image in GIMP and examine pixel 0,0 the rgb values are r: 45, g: 203, b: 203. However, if I use Jimp and the following code:

Jimp.read(fileToRead)
          .then(image => {
            console.log(Jimp.intToRGBA(image.getPixelColor(0,0)))
          })
          .catch(err => {
            console.log(err);
          })

I get { r: 173, g: 200, b: 150, a: 255 }

By eye, r: 45, g: 203, b: 203 is the correct color. So what am I doing wrong? Do I need to use some option to tell Jimp it's 24-bit? Can Jimp read 24-bit? Internally it's using node mod bmp-js which supposedly can decode 24 bit. Am I missing some basic knowledge about bmp format?

Thanks.

Contributor guide

Research direction
Investigate Jimp's BMP decoding logic in the source code (likely in packages/core/src/image/bitmap.js or similar) and compare with the bmp js library used internally. Check if there is a byte order (little endian vs big endian) or color space conversion issue. Also verify the expected RGB values using a known working BMP reader.
Tech stack
javascript
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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.
Clear
Prerequisites
None
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20