How to combine individual R,G,B channels into 16bit output?

Author: mwilmesCreated Aug 5, 2021Updated Jul 12, 2026

Labelsquestion

What are you trying to achieve?

Selectively extracting single R,G and B channels from three different 16bit input tiff files. Then combining them to a new 16bit output tiff. With srgb output color space (8bit) everything works as expected. As I switch to rgb16 colourspace for output I get a pure black image.

Have you searched for similar questions?

Yes but nothing yet seems to point me on what I'm doing wrong.

Are you able to provide a minimal, standalone code sample that demonstrates this question?

javascript

    Promise.all([
        sharp('input1.tif')
            .extractChannel('red')
            .toColourspace('b-w')
            .toBuffer(),
        sharp('input2.tif')
            .extractChannel('green')
            .toColourspace('b-w')
            .toBuffer(),
        sharp('input3.tif')
        .extractChannel('blue')
            .toColourspace('b-w')
            .toBuffer()
        ])
        .then(images => {
            sharp(images[0])
                .joinChannel([
                    images[1],
                    images[2]
                ])
                //.toColorspace('srgb')
                .toColorspace('rgb16')
                .tiff({
                    compression: 'none'
                })
                .toFile('output.tif');
        });

Output file:

Are you able to provide a sample image that helps explain the question?

Too large of files.

Source: lovell/sharp

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