[Feat] image2image for Z-Image (#1580)

Signed-off-by: Lancer <maruixiang6688@gmail.com>
Signed-off-by: Lancer <402430575@qq.com>

examples/offline_inference/image_to_image/image_to_image.md

@@ -51,5 +51,6 @@ Key arguments:
 - `--vae-use-tiling`: enable VAE tiling for memory optimization.
 - `--cfg-parallel-size`: set it to 2 to enable CFG Parallel. See more examples in [`user_guide`](../../../docs/user_guide/diffusion/parallelism_acceleration.md#cfg-parallel).
 - `--enable-cpu-offload`: enable CPU offloading for diffusion models.
+- `--strength`: **Z-Image only** - controls the denoising start timestep for I2I (default: 0.6). Range: [0.0, 1.0]. Lower values preserve more of the original image; higher values allow more creative changes.
 
 > ℹ️ If you encounter OOM errors, try using `--vae-use-slicing` and `--vae-use-tiling` to reduce memory usage.

examples/online_serving/image_to_image/README.md

@@ -314,6 +314,7 @@ count, use `size` and `n` rather than `height`, `width`, or
 | `seed`                   | int   | None    | Random seed (reproducible)            |
 | `negative_prompt`        | str   | None    | Negative prompt                       |
 | `num_outputs_per_prompt` | int   | 1       | Number of images to generate          |
+| `strength`               | float | 0.6     | **Z-Image only** - Denoising start timestep for I2I. Range: [0.0, 1.0]. Lower preserves more of original image. |
 | `layers`                 | int   | 4       | Number of layers (Qwen-Image-Layered) |
 | `resolution`             | int   | 640     | Resolution, 640 or 1024 (Qwen-Image-Layered) |