I’m using Spectacle on Linux and it doesn’t seem to add anything to the metadata.
- 150% scale factor: https://www.metadata2go.com/result#j=f7c666d9-89bb-4cca-bce1-32109b188ea8
- 100%: https://www.metadata2go.com/result#j=1f4ce715-44a6-4c49-a7f0-5204f84dc8a0
The code from that gist returns false for a screenshot I created on my Linux system with a scale factor of 150%. The pHYs chunk of that image looks like this:
{ xDpu: 3780, yDpu: 3780, xDpi: 96, yDpi: 96, unit: 'meter' }