#170 alpha channel for spectrograms

[Marlon Schumacher]

Dear Sox-developers,

Would it be possible to add an 'alpha' channel for spectrograms, e.g. in order to turn all the white/very bright colours transparent?
This way it would be possible to overlay them and display them on different backgrounds. I've attached an image.

Marlon

[Marlon Schumacher]

sox-spectrogram with alpha channel

[Martin Guy]

https://codeberg.org/sox_ng/sox_ng/issues/716

However, from the attachment, it looks like everything is transparent except for pixels over a certain loudness, not the opposite as the description seems to say.
Am I understanding correctly?

If you're still with us, I'm more likely to notice a comment there than here.