From 4314f9101a2f3bd7f11ba4290d2a7e2e64b4ceea Mon Sep 17 00:00:00 2001
From: Katherine Crowson <crowsonkb@gmail.com>
Date: Wed, 23 Nov 2022 09:32:43 -0800
Subject: [PATCH] Add CompVisVDenoiser wrapper

---
 k_diffusion/external.py | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/k_diffusion/external.py b/k_diffusion/external.py
index 2f1d258..79b51ce 100644
--- a/k_diffusion/external.py
+++ b/k_diffusion/external.py
@@ -136,3 +136,42 @@ def __init__(self, model, quantize=False, device='cpu'):
 
     def get_eps(self, *args, **kwargs):
         return self.inner_model.apply_model(*args, **kwargs)
+
+
+class DiscreteVDDPMDenoiser(DiscreteSchedule):
+    """A wrapper for discrete schedule DDPM models that output v."""
+
+    def __init__(self, model, alphas_cumprod, quantize):
+        super().__init__(((1 - alphas_cumprod) / alphas_cumprod) ** 0.5, quantize)
+        self.inner_model = model
+        self.sigma_data = 1.
+
+    def get_scalings(self, sigma):
+        c_skip = self.sigma_data ** 2 / (sigma ** 2 + self.sigma_data ** 2)
+        c_out = -sigma * self.sigma_data / (sigma ** 2 + self.sigma_data ** 2) ** 0.5
+        c_in = 1 / (sigma ** 2 + self.sigma_data ** 2) ** 0.5
+        return c_skip, c_out, c_in
+
+    def get_v(self, *args, **kwargs):
+        return self.inner_model(*args, **kwargs)
+
+    def loss(self, input, noise, sigma, **kwargs):
+        c_skip, c_out, c_in = [utils.append_dims(x, input.ndim) for x in self.get_scalings(sigma)]
+        noised_input = input + noise * utils.append_dims(sigma, input.ndim)
+        model_output = self.get_v(noised_input * c_in, self.sigma_to_t(sigma), **kwargs)
+        target = (input - c_skip * noised_input) / c_out
+        return (model_output - target).pow(2).flatten(1).mean(1)
+
+    def forward(self, input, sigma, **kwargs):
+        c_skip, c_out, c_in = [utils.append_dims(x, input.ndim) for x in self.get_scalings(sigma)]
+        return self.get_v(input * c_in, self.sigma_to_t(sigma), **kwargs) * c_out + input * c_skip
+
+
+class CompVisVDenoiser(DiscreteVDDPMDenoiser):
+    """A wrapper for CompVis diffusion models that output v."""
+
+    def __init__(self, model, quantize=False, device='cpu'):
+        super().__init__(model, model.alphas_cumprod, quantize=quantize)
+
+    def get_v(self, x, t, cond, **kwargs):
+        return self.inner_model.apply_model(x, t, cond)