[Feature] Support of perceptual loss in style transfer

[Taited]

The manipulation of images could be seen as a conditioned generation. Therefore, the commonly used perceptual loss in style transfer is essential in some generation tasks. However, the mmgeneration only supports perceptual loss in the LPIP metric.

Is it possible to support the perceptual loss for style transfer as in the mmediting?

[zengyh1900]

Please check this issue. Have we support perceptual loss in MMGeneration?

[plyfager]

Sure, it's an commonly used feature. We will add this to backlog. We will appreciate it a lot if you'd like to make a PR.

[Taited]

Thank you for your response. I am very willing to make a PR for adapting the perceptual loss from mmediting to mmgeneration. However, I have a few issues that need to discuss first.

1. Should the perceptual loss be implemented within mmgen/models/losses/gen_auxiliary_loss.py? Or I should create a new file like mmgen/models/losses/perceptual_loss.py
2. Should the class name PerceptualLoss be distinguished from the one in LPIP's PerceptualLoss? If it is true, what's your suggestions with the name?

[plyfager]

Here are my suggestion.

1. You may implement the perceptual loss within mmgen/models/losses/gen_auxiliary_loss.py, then you can add it to your training config.
2. Since perceptual loss here is mainly used to calculate PPL metric. You may just use the same class name.

[plyfager]

3. In 1.x, we just remove PeceptualLoss class and use lpips package instead. You may also use this package for your class.

[plyfager]

Since now we are merging this repo into MMEditing. I also recommend you to try MMEdit-1.x and add this loss item there :).

[Taited]

Thank you for your suggestions.

I have a problem with the returned values. Typically, a loss module in mmgeneration returns one value. However, the PerceptualLoss often returns loss_percep and loss_style. Should the PerceptualLoss return a sum of these two losses or should I separate the loss_style into another loss module?