diffusers#4003 Subtract one from our intended step goal, when we are provided a defined timestep to begin on.

Author: bghira

src/diffusers/pipelines/stable_diffusion_xl/pipeline_stable_diffusion_xl_img2img.py

@@ -883,6 +883,10 @@ def __call__(
         image = self.image_processor.preprocess(image)
 
         # 5. Prepare timesteps
+        if begin_inference_step is not None:
+            # In Diffusers pipelines, each generation always does ONE more step than asked.
+            # As a result, we need to reduce the number of steps we do for this subsequent by one, to remain aligned.
+            num_inference_steps -= 1
         self.scheduler.set_timesteps(num_inference_steps, device=device)
         timesteps, num_inference_steps = self.get_timesteps(num_inference_steps, begin_inference_step, strength, device)
         latent_timestep = timesteps[:1].repeat(batch_size * num_images_per_prompt)