Support Latent Consistency Models, generate image in 4 steps

[frankyifei]

https://latent-consistency-models.github.io/
Seems quite promising and interesting. the quality of image seems decent in 4 steps.

[marclove]

This is possible already by loading the LCM as a Lora. I learned how to do it here.

It is a little awkward for the workflow. I haven't ventured into writing custom nodes yet, but it would be nice to have an LCM-specific node that let you toggle it on/off, since LCMs are great for exploring and prototyping parameters & workflows before doing a higher quality non-LCM generation.