if the image is a QR code or contains a QR code, the result is larger than the original image.

[Minglu-Huo]

When I use Sharp to compress PNG images, I find that if the image is a QR code or contains a QR code, after I use sharp(file.buffer).png({ quality: 80 }).toBuffer() for compression, the result is larger than the original image. This is not the outcome I expected. What should I do to address this?

[ayushmourya]

For QR codes, avoid lossy compression as it can increase file size. Use lossless compression instead with Sharp: sharp(file.buffer).png({ compressionLevel: 9, adaptiveFiltering: true, palette: true }).toBuffer() This applies maximum lossless compression, adaptive filtering, and palette conversion, which is more suitable for QR codes. Always test the compressed images to ensure they remain scannable.

[lovell]

If you know your output PNG will contain only 2 possible pixel values then you can limit the palette to a relevant size:

const output = await sharp(input).png({ colours: 2 }).toBuffer();

This reduces the file size of the sample image provided from 11441 bytes to 5209 bytes.

https://sharp.pixelplumbing.com/api-output#png

[lovell]

I hope this information helped. Please feel free to re-open with more details if further assistance is required.

[Minglu-Huo]

@lovell Thank you very much for your help. I think I should first identify whether the image contains a QR code, and then use the configuration you provided to compress it.