Unexpected image rotation

[katerynaHutyryak]

I'm using jpeg-js library to decode an image, apply my own greyscale filter, and encode it back. But unfortunately every vertical picture I process for some reason is rotated and saved horizontally (while horizontal images preserve its correct rotation and are totally ok). Here's my code:

`function greyscale(width, height, data, bytesPerPixel, imageName) {
const bwPixelData = Buffer.alloc(data.length)

for (let vrt = 0; vrt < height; vrt++) {
    for (let hrz = 0; hrz < width; hrz++) {
        const offset = (vrt * width + hrz) * bytesPerPixel
        
        const red = data[offset]
        const green = data[offset + 1]
        const blue = data[offset + 2]
        
        const bwPixel = Math.round((red + green + blue) / 3.0)
        
        bwPixelData[offset] = bwPixel
        bwPixelData[offset + 1] = bwPixel
        bwPixelData[offset + 2] = bwPixel
        
    }
}

const filteredImageName = encodeImage(bwPixelData, width, height, imageName)
return filteredImageName

}
exports.decodeImage = function(name, path) {
if (name.match(/.*.jpe?g/i)){
const jpegData = fs.readFileSync(path)
return jpeg.decode(jpegData)
} else {
throw new Error('Unsupported Media Type')
}
}

exports.encodeImage = function(data, width, height, imageName) {

const filteredImageName = `outfile-${imageName}`

const rawImageData = {
    data: data,
    width: width,
    height: height,
}


const jpegImageData = jpeg.encode(rawImageData, 50)

try {
    fs.writeFileSync(`${outputPath}/${filteredImageName}`, jpegImageData.data);
    console.log('File written successfully');
} catch (error) {
    console.error('Error writing file:', error);
}

return filteredImageName

} `

At first I thought that the problem might be hidden in the greyscale function and how I process pixels. So I tried to decode, encode, and save back an original, unfiltered, vertical photo, which had lead to the same result: unexpected rotation.

Have you ever faced a problem like this and does anyone know how to fix it? It's also important to me to use a pure js implementation instead of libraries like Sharp