dreamega-bmp-codec

Pure JavaScript BMP encoder and decoder. Read and write BMP files in the browser or Node.js.

Extracted from Dreamega - an AI content creation platform.

Installation

npm install dreamega-bmp-codec

Usage

Encoding (ImageData to BMP)

import { encodeBMP } from "dreamega-bmp-codec";

// Get ImageData from a canvas
const canvas = document.querySelector("canvas")!;
const ctx = canvas.getContext("2d")!;
const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);

// Encode to BMP
const bmpBlob = encodeBMP(imageData);

// Download
const url = URL.createObjectURL(bmpBlob);
const a = document.createElement("a");
a.href = url;
a.download = "output.bmp";
a.click();

Decoding (BMP to ImageData)

import { decodeBMP } from "dreamega-bmp-codec";

// Read a BMP file
const file = inputElement.files[0];
const buffer = await file.arrayBuffer();
const imageData = decodeBMP(buffer);

// Draw to canvas
const canvas = document.createElement("canvas");
canvas.width = imageData.width;
canvas.height = imageData.height;
canvas.getContext("2d")!.putImageData(imageData, 0, 0);

API

encodeBMP(imageData: ImageData): Blob

Encode ImageData to a 24-bit BMP file.

• 14-byte file header + 40-byte BITMAPINFOHEADER
• 24-bit color (BGR format)
• Bottom-to-top row order
• Row padding to 4-byte alignment
• 72 DPI resolution (2835 pixels/meter)

decodeBMP(buffer: ArrayBuffer): ImageData

Decode a BMP file to ImageData.

• Supports 24-bit and 32-bit uncompressed BMPs
• Handles both bottom-to-top and top-to-bottom row order
• Validates BMP headers and data integrity

BMP Format Details

The BMP file format consists of:

1. File Header (14 bytes): "BM" signature, file size, pixel data offset
2. Info Header (40 bytes): dimensions, bit depth, compression, resolution
3. Pixel Data: BGR(A) pixels, rows padded to 4-byte boundaries

Features

• Zero dependencies
• Works in browser and Node.js (with ImageData polyfill)
• Correct BMP binary format with proper headers
• Handles row padding for all image widths

License

MIT - see LICENSE