High-resolution image generation with Segmind-VegaRT and OpenVINO#

This Jupyter notebook can be launched after a local installation only.


The Segmind Vega Model is a distilled version of the Stable Diffusion XL (SDXL), offering a remarkable 70% reduction in size and an impressive speedup while retaining high-quality text-to-image generation capabilities. Segmind Vega marks a significant milestone in the realm of text-to-image models, setting new standards for efficiency and speed. Engineered with a compact yet powerful design, it boasts only 745 million parameters. This streamlined architecture not only makes it the smallest in its class but also ensures lightning-fast performance, surpassing the capabilities of its predecessors. Vega represents a breakthrough in model optimization. Its compact size, compared to the 859 million parameters of the SD 1.5 and the hefty 2.6 billion parameters of SDXL, maintains a commendable balance between size and performance. Vega’s ability to deliver high-quality images rapidly makes it a game-changer in the field, offering an unparalleled blend of speed, efficiency, and precision.

Segmind Vega is a symmetrical, distilled version of the SDXL model; it is over 70% smaller and ~100% faster. The Down Block contains 247 million parameters, the Mid Block has 31 million, and the Up Block has 460 million. Apart from the size difference, the architecture is virtually identical to that of SDXL, ensuring compatibility with existing interfaces requiring no or minimal adjustments. Although smaller than the SD1.5 Model, Vega supports higher-resolution generation due to the SDXL architecture, making it an ideal replacement for Stable Diffusion 1.5

Segmind VegaRT is a distilled LCM-LoRA adapter for the Vega model, that allowed us to reduce the number of inference steps required to generate a good quality image to somewhere between 2 - 8 steps. Latent Consistency Model (LCM) LoRA was proposed in LCM-LoRA: A universal Stable-Diffusion Acceleration Module by Simian Luo, Yiqin Tan, Suraj Patil, Daniel Gu et al.

More details about models can be found in Segmind blog post

In this tutorial, we explore how to run and optimize Segmind-VegaRT with OpenVINO. We will use a pre-trained model from the Hugging Face Diffusers library. To simplify the user experience, the Hugging Face Optimum Intel library is used to convert the models to OpenVINO™ IR format. Additionally, we demonstrate how to improve pipeline latency with the quantization UNet model using NNCF.

Table of contents:#


%pip install -q --extra-index-url https://download.pytorch.org/whl/cpu\
"torch>=2.1" transformers diffusers "git+https://github.com/huggingface/optimum-intel.git" "gradio>=4.19" "openvino>=2023.3.0" "peft==0.6.2"
WARNING: Skipping openvino-dev as it is not installed.
WARNING: Skipping openvino as it is not installed.
Note: you may need to restart the kernel to use updated packages.
Note: you may need to restart the kernel to use updated packages.

Prepare PyTorch model#

For preparing Segmind-VegaRT model for inference, we should create Segmind-Vega pipeline first. After that, for enabling Latent Consistency Model capability, we should integrate VegaRT LCM adapter using add_lora_weights method and replace scheduler with LCMScheduler. For simplification of these steps for next notebook running, we save created pipeline on disk.

import torch
from diffusers import LCMScheduler, AutoPipelineForText2Image
import gc
from pathlib import Path

model_id = "segmind/Segmind-Vega"
adapter_id = "segmind/Segmind-VegaRT"
pt_model_dir = Path("segmind-vegart")

if not pt_model_dir.exists():
    pipe = AutoPipelineForText2Image.from_pretrained(model_id, torch_dtype=torch.float16, variant="fp16")
    pipe.scheduler = LCMScheduler.from_config(pipe.scheduler.config)

    del pipe
2024-01-24 14:12:38.551058: I tensorflow/core/util/port.cc:110] oneDNN custom operations are on. You may see slightly different numerical results due to floating-point round-off errors from different computation orders. To turn them off, set the environment variable TF_ENABLE_ONEDNN_OPTS=0.
2024-01-24 14:12:38.591203: I tensorflow/core/platform/cpu_feature_guard.cc:182] This TensorFlow binary is optimized to use available CPU instructions in performance-critical operations.
To enable the following instructions: AVX2 AVX512F AVX512_VNNI FMA, in other operations, rebuild TensorFlow with the appropriate compiler flags.
2024-01-24 14:12:39.344351: W tensorflow/compiler/tf2tensorrt/utils/py_utils.cc:38] TF-TRT Warning: Could not find TensorRT

Convert model to OpenVINO format#

We will use optimum-cli interface for exporting it into OpenVINO Intermediate Representation (IR) format.

Optimum CLI interface for converting models supports export to OpenVINO (supported starting optimum-intel 1.12 version). General command format:

optimum-cli export openvino --model <model_id_or_path> --task <task> <output_dir>

where task is task to export the model for, if not specified, the task will be auto-inferred based on the model. Available tasks depend on the model, as Segmind-Vega uses interface compatible with SDXL, we should be selected stable-diffusion-xl

You can find a mapping between tasks and model classes in Optimum TaskManager documentation.

Additionally, you can specify weights compression --fp16 for the compression model to FP16 and --int8 for the compression model to INT8. Please note, that for INT8, it is necessary to install nncf.

Full list of supported arguments available via --help For more details and examples of usage, please check optimum documentation.

For Tiny Autoencoder, we will use ov.convert_model function for obtaining ov.Model and save it using ov.save_model. Model consists of 2 parts that used in pipeline separately: vae_encoder for encoding input image in latent space in image-to-image generation task and vae_decoder that responsible for decoding diffusion result back to image format.

from pathlib import Path

model_dir = Path("openvino-segmind-vegart")
sdxl_model_id = "./segmind-vegart"
tae_id = "madebyollin/taesdxl"
skip_convert_model = model_dir.exists()
import torch
import openvino as ov
from diffusers import AutoencoderTiny
import gc

class VAEEncoder(torch.nn.Module):
    def __init__(self, vae):
        self.vae = vae

    def forward(self, sample):
        return self.vae.encode(sample)

class VAEDecoder(torch.nn.Module):
    def __init__(self, vae):
        self.vae = vae

    def forward(self, latent_sample):
        return self.vae.decode(latent_sample)

def convert_tiny_vae(model_id, output_path):
    tiny_vae = AutoencoderTiny.from_pretrained(model_id)
    vae_encoder = VAEEncoder(tiny_vae)
    ov_model = ov.convert_model(vae_encoder, example_input=torch.zeros((1, 3, 512, 512)))
    ov.save_model(ov_model, output_path / "vae_encoder/openvino_model.xml")
    tiny_vae.save_config(output_path / "vae_encoder")
    vae_decoder = VAEDecoder(tiny_vae)
    ov_model = ov.convert_model(vae_decoder, example_input=torch.zeros((1, 4, 64, 64)))
    ov.save_model(ov_model, output_path / "vae_decoder/openvino_model.xml")
    tiny_vae.save_config(output_path / "vae_decoder")
    del tiny_vae
    del ov_model

if not skip_convert_model:
    !optimum-cli export openvino --model $sdxl_model_id --task stable-diffusion-xl $model_dir --fp16
    convert_tiny_vae(tae_id, model_dir)

Text-to-image generation#

Text-to-image generation lets you create images using text description. To start generating images, we need to load models first. To load an OpenVINO model and run an inference with Optimum and OpenVINO Runtime, you need to replace diffusers StableDiffusionXLPipeline with Optimum OVStableDiffusionXLPipeline. Pipeline initialization starts with using from_pretrained method, where a directory with OpenVINO models should be passed. Additionally, you can specify an inference device.

For saving time, we will not cover image-to-image generation in this notebook. As we already mentioned, Segmind-Vega is compatible with Stable Diffusion XL pipeline, the steps required to run Stable Diffusion XL inference for image-to-image task were discussed in this notebook.

Select inference device for text-to-image generation#

import ipywidgets as widgets

core = ov.Core()

device = widgets.Dropdown(
    options=core.available_devices + ["AUTO"],

Dropdown(description='Device:', index=3, options=('CPU', 'GPU.0', 'GPU.1', 'AUTO'), value='AUTO')
from optimum.intel.openvino import OVStableDiffusionXLPipeline

text2image_pipe = OVStableDiffusionXLPipeline.from_pretrained(model_dir, device=device.value)
INFO:nncf:NNCF initialized successfully. Supported frameworks detected: torch, tensorflow, onnx, openvino
The config attributes {'interpolation_type': 'linear', 'skip_prk_steps': True, 'use_karras_sigmas': False} were passed to LCMScheduler, but are not expected and will be ignored. Please verify your scheduler_config.json configuration file.
Compiling the vae_decoder to AUTO ...
Compiling the unet to AUTO ...
Compiling the text_encoder_2 to AUTO ...
Compiling the vae_encoder to AUTO ...
Compiling the text_encoder to AUTO ...
from transformers import set_seed


prompt = "A cinematic highly detailed shot of a baby Yorkshire terrier wearing an intricate Italian priest robe, with crown"
image = text2image_pipe(prompt, num_inference_steps=4, height=512, width=512, guidance_scale=0.5).images[0]
0%|          | 0/4 [00:00<?, ?it/s]
del text2image_pipe


NNCF enables post-training quantization by adding quantization layers into model graph and then using a subset of the training dataset to initialize the parameters of these additional quantization layers. Quantized operations are executed in INT8 instead of FP32/FP16 making model inference faster.

According to Segmind-VEGAModel structure, the UNet model takes up significant portion of the overall pipeline execution time. Now we will show you how to optimize the UNet part using NNCF to reduce computation cost and speed up the pipeline. Quantizing the rest of the SDXL pipeline does not significantly improve inference performance but can lead to a substantial degradation of accuracy.

The optimization process contains the following steps:

  1. Create a calibration dataset for quantization.

  2. Run nncf.quantize() to obtain quantized model.

  3. Save the INT8 model using openvino.save_model() function.

Please select below whether you would like to run quantization to improve model inference speed.

to_quantize = widgets.Checkbox(

Checkbox(value=True, description='Quantization')
# Fetch `skip_kernel_extension` module
import requests

r = requests.get(
open("skip_kernel_extension.py", "w").write(r.text)

int8_pipe = None

if to_quantize.value and "GPU" in device.value:
    to_quantize.value = False
%load_ext skip_kernel_extension

Prepare calibration dataset#

We use a portion of conceptual_captions dataset from Hugging Face as calibration data. To collect intermediate model inputs for calibration we should customize CompiledModel.

UNET_INT8_OV_PATH = model_dir / "optimized_unet" / "openvino_model.xml"

def disable_progress_bar(pipeline, disable=True):
    if not hasattr(pipeline, "_progress_bar_config"):
        pipeline._progress_bar_config = {"disable": disable}
        pipeline._progress_bar_config["disable"] = disable
%%skip not $to_quantize.value

import datasets
import numpy as np
from tqdm.notebook import tqdm
from transformers import set_seed
from typing import Any, Dict, List


class CompiledModelDecorator(ov.CompiledModel):
    def __init__(self, compiled_model: ov.CompiledModel, data_cache: List[Any] = None):
        self.data_cache = data_cache if data_cache else []

    def __call__(self, *args, **kwargs):
        return super().__call__(*args, **kwargs)

def collect_calibration_data(pipe, subset_size: int) -> List[Dict]:
    original_unet = pipe.unet.request
    pipe.unet.request = CompiledModelDecorator(original_unet)

    dataset = datasets.load_dataset("conceptual_captions", split="train").shuffle(seed=42)

    # Run inference for data collection
    pbar = tqdm(total=subset_size)
    diff = 0
    for batch in dataset:
        prompt = batch["caption"]
        if len(prompt) > pipe.tokenizer.model_max_length:
        _ = pipe(
        collected_subset_size = len(pipe.unet.request.data_cache)
        if collected_subset_size >= subset_size:
            pbar.update(subset_size - pbar.n)
        pbar.update(collected_subset_size - diff)
        diff = collected_subset_size

    calibration_dataset = pipe.unet.request.data_cache
    disable_progress_bar(pipe, disable=False)
    pipe.unet.request = original_unet
    return calibration_dataset
%%skip not $to_quantize.value

if not UNET_INT8_OV_PATH.exists():
    text2image_pipe = OVStableDiffusionXLPipeline.from_pretrained(model_dir, device=device.value)
    unet_calibration_data = collect_calibration_data(text2image_pipe, subset_size=200)

Run quantization#

Create a quantized model from the pre-trained converted OpenVINO model. Quantization of the first and last Convolution layers impacts the generation results. We recommend using IgnoredScope to keep accuracy sensitive Convolution layers in FP16 precision.

NOTE: Quantization is time and memory consuming operation. Running quantization code below may take some time.

%%skip not $to_quantize.value

import nncf
from nncf.scopes import IgnoredScope

UNET_OV_PATH = model_dir / "unet" / "openvino_model.xml"
if not UNET_INT8_OV_PATH.exists():
    unet = core.read_model(UNET_OV_PATH)
    quantized_unet = nncf.quantize(
    ov.save_model(quantized_unet, UNET_INT8_OV_PATH)
%%skip not $to_quantize.value

def create_int8_pipe(model_dir, unet_int8_path, device, core, unet_device='CPU'):
    int8_pipe = OVStableDiffusionXLPipeline.from_pretrained(model_dir, device=device, compile=True)
    del int8_pipe.unet.request
    del int8_pipe.unet.model
    int8_pipe.unet.model = core.read_model(unet_int8_path)
    int8_pipe.unet.request = core.compile_model(int8_pipe.unet.model, unet_device or device)
    return int8_pipe

int8_text2image_pipe = create_int8_pipe(model_dir, UNET_INT8_OV_PATH, device.value, core)


image = int8_text2image_pipe(prompt, num_inference_steps=4, height=512, width=512, guidance_scale=0.5).images[0]
The config attributes {'interpolation_type': 'linear', 'skip_prk_steps': True, 'use_karras_sigmas': False} were passed to LCMScheduler, but are not expected and will be ignored. Please verify your scheduler_config.json configuration file.
Compiling the vae_decoder to AUTO ...
Compiling the unet to AUTO ...
Compiling the text_encoder to AUTO ...
Compiling the text_encoder_2 to AUTO ...
Compiling the vae_encoder to AUTO ...
0%|          | 0/4 [00:00<?, ?it/s]

Compare UNet file size#

%%skip not $to_quantize.value

fp16_ir_model_size = UNET_OV_PATH.with_suffix(".bin").stat().st_size / 1024
quantized_model_size = UNET_INT8_OV_PATH.with_suffix(".bin").stat().st_size / 1024

print(f"FP16 model size: {fp16_ir_model_size:.2f} KB")
print(f"INT8 model size: {quantized_model_size:.2f} KB")
print(f"Model compression rate: {fp16_ir_model_size / quantized_model_size:.3f}")
FP16 model size: 1455519.49 KB
INT8 model size: 729448.00 KB
Model compression rate: 1.995

To measure the inference performance of the FP16 and INT8 pipelines, we use median inference time on the calibration subset.

NOTE: For the most accurate performance estimation, it is recommended to run benchmark_app in a terminal/command prompt after closing other applications.

%%skip not $to_quantize.value

import time

validation_size = 7
calibration_dataset = datasets.load_dataset("conceptual_captions", split="train")
validation_data = []
for idx, batch in enumerate(calibration_dataset):
    if idx >= validation_size:
    prompt = batch["caption"]

def calculate_inference_time(pipe, dataset):
    inference_time = []

    for prompt in dataset:
        start = time.perf_counter()
        image = pipe(
        end = time.perf_counter()
        delta = end - start
    disable_progress_bar(pipe, disable=False)
    return np.median(inference_time)
/home/ea/work/openvino_notebooks/test_env/lib/python3.8/site-packages/datasets/table.py:1421: FutureWarning: promote has been superseded by mode='default'.
  table = cls._concat_blocks(blocks, axis=0)
%%skip not $to_quantize.value

int8_latency = calculate_inference_time(int8_text2image_pipe, validation_data)

del int8_text2image_pipe

text2image_pipe = OVStableDiffusionXLPipeline.from_pretrained(model_dir, device=device.value)
fp_latency = calculate_inference_time(text2image_pipe, validation_data)

del text2image_pipe
print(f"FP16 pipeline latency: {fp_latency:.3f}")
print(f"INT8 pipeline latency: {int8_latency:.3f}")
print(f"Text-to-Image generation speed up: {fp_latency / int8_latency:.3f}")
The config attributes {'interpolation_type': 'linear', 'skip_prk_steps': True, 'use_karras_sigmas': False} were passed to LCMScheduler, but are not expected and will be ignored. Please verify your scheduler_config.json configuration file.
Compiling the vae_decoder to AUTO ...
Compiling the unet to AUTO ...
Compiling the text_encoder to AUTO ...
Compiling the text_encoder_2 to AUTO ...
Compiling the vae_encoder to AUTO ...
FP16 pipeline latency: 11.029
INT8 pipeline latency: 5.967
Text-to-Image generation speed up: 1.849

Interactive Demo#

Now, you can check model work using own text descriptions. Provide text prompt in the text box and launch generation using Run button. Additionally you can control generation with additional parameters: * Seed - random seed for initialization * Steps - number of generation steps * Height and Width - size of generated image

Please select below whether you would like to use the quantized model to launch the interactive demo.

quantized_model_present = UNET_INT8_OV_PATH.exists()

use_quantized_model = widgets.Checkbox(
    description="Use quantized model",
    disabled=not quantized_model_present,

Checkbox(value=True, description='Use quantized model')
import gradio as gr

if use_quantized_model.value:
    if not quantized_model_present:
        raise RuntimeError("Quantized model not found.")
    text2image_pipe = create_int8_pipe(model_dir, UNET_INT8_OV_PATH, device.value, core)

    text2image_pipe = OVStableDiffusionXLPipeline.from_pretrained(model_dir, device=device.value)

def generate_from_text(text, seed, num_steps, height, width):
    result = text2image_pipe(
    return result

with gr.Blocks() as demo:
    with gr.Column():
        positive_input = gr.Textbox(label="Text prompt")
        with gr.Row():
            seed_input = gr.Number(precision=0, label="Seed", value=42, minimum=0)
            steps_input = gr.Slider(label="Steps", value=4, minimum=2, maximum=8, step=1)
            height_input = gr.Slider(label="Height", value=512, minimum=256, maximum=1024, step=32)
            width_input = gr.Slider(label="Width", value=512, minimum=256, maximum=1024, step=32)
            btn = gr.Button()
        out = gr.Image(
            label=("Result (Quantized)" if use_quantized_model.value else "Result (Original)"),
            [positive_input, seed_input, steps_input, height_input, width_input],
                ["cute cat", 999],
                    "underwater world coral reef, colorful jellyfish, 35mm, cinematic lighting, shallow depth of field,  ultra quality, masterpiece, realistic",
                    "a photo realistic happy white poodle dog ​​playing in the grass, extremely detailed, high res, 8k, masterpiece, dynamic angle",
                    "Astronaut on Mars watching sunset, best quality, cinematic effects,",
                    "Black and white street photography of a rainy night in New York, reflections on wet pavement",
                    "cinematic photo detailed closeup portraid of a Beautiful cyberpunk woman, robotic parts, cables, lights, text; , high quality photography, 3 point lighting, flash with softbox, 4k, Canon EOS R3, hdr, smooth, sharp focus, high resolution, award winning photo, 80mm, f2.8, bokeh . 35mm photograph, film, bokeh, professional, 4k, highly detailed, high quality photography, 3 point lighting, flash with softbox, 4k, Canon EOS R3, hdr, smooth, sharp focus, high resolution, award winning photo, 80mm, f2.8, bokeh",
            [positive_input, seed_input],

# if you are launching remotely, specify server_name and server_port
# demo.launch(server_name='your server name', server_port='server port in int')
# Read more in the docs: https://gradio.app/docs/
# if you want create public link for sharing demo, please add share=True
except Exception:
    demo.launch(share=True, debug=False)