Fix image upcasting (#7858)

Fix image's upcasting before `vae.encode()` when using `fp16`

Co-authored-by: YiYi Xu <yixu310@gmail.com>

src/diffusers/pipelines/ledits_pp/pipeline_leditspp_stable_diffusion_xl.py

@@ -1419,7 +1419,6 @@ class LEditsPPPipelineStableDiffusionXL(
         if needs_upcasting:
             image = image.float()
             self.upcast_vae()
-            image = image.to(next(iter(self.vae.post_quant_conv.parameters())).dtype)
 
         x0 = self.vae.encode(image).latent_dist.mode()
         x0 = x0.to(dtype)

src/diffusers/pipelines/stable_diffusion_xl/pipeline_stable_diffusion_xl_instruct_pix2pix.py

@@ -525,8 +525,8 @@ class StableDiffusionXLInstructPix2PixPipeline(
             # make sure the VAE is in float32 mode, as it overflows in float16
             needs_upcasting = self.vae.dtype == torch.float16 and self.vae.config.force_upcast
             if needs_upcasting:
+                image = image.float()
                 self.upcast_vae()
-                image = image.to(next(iter(self.vae.post_quant_conv.parameters())).dtype)
 
             image_latents = retrieve_latents(self.vae.encode(image), sample_mode="argmax")