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Monodepth Estimation with OpenVINO

This tutorial demonstrates Monocular Depth Estimation with MidasNet in OpenVINO. Model information can be found here.

monodepth

What is Monodepth?

Monocular Depth Estimation is the task of estimating scene depth using a single image. It has many potential applications in robotics, 3D reconstruction, medical imaging and autonomous systems. For this demo, we use a neural network model called MiDaS which was developed by the Embodied AI Foundation. Check out the research paper below to learn more.

R. Ranftl, K. Lasinger, D. Hafner, K. Schindler and V. Koltun, “Towards Robust Monocular Depth Estimation: Mixing Datasets for Zero-shot Cross-dataset Transfer,” in IEEE Transactions on Pattern Analysis and Machine Intelligence, doi: 10.1109/TPAMI.2020.3019967.

Preparation

Imports

import sys
import time
from pathlib import Path

import cv2
import matplotlib.cm
import matplotlib.pyplot as plt
import numpy as np
from IPython.display import (
    HTML,
    FileLink,
    Pretty,
    ProgressBar,
    Video,
    clear_output,
    display,
)
from openvino.runtime import Core

sys.path.append("../utils")
from notebook_utils import load_image

Settings

DEVICE = "CPU"
MODEL_FILE = "model/MiDaS_small.xml"

model_xml_path = Path(MODEL_FILE)

Functions

def normalize_minmax(data):
    """Normalizes the values in `data` between 0 and 1"""
    return (data - data.min()) / (data.max() - data.min())


def convert_result_to_image(result, colormap="viridis"):
    """
    Convert network result of floating point numbers to an RGB image with
    integer values from 0-255 by applying a colormap.

    `result` is expected to be a single network result in 1,H,W shape
    `colormap` is a matplotlib colormap.
    See https://matplotlib.org/stable/tutorials/colors/colormaps.html
    """
    cmap = matplotlib.cm.get_cmap(colormap)
    result = result.squeeze(0)
    result = normalize_minmax(result)
    result = cmap(result)[:, :, :3] * 255
    result = result.astype(np.uint8)
    return result


def to_rgb(image_data) -> np.ndarray:
    """
    Convert image_data from BGR to RGB
    """
    return cv2.cvtColor(image_data, cv2.COLOR_BGR2RGB)

Load the Model

Load the model in Inference Engine with ie.read_model and compile it for the specified device with ie.compile_model. Get input and output keys and the expected input shape for the model.

ie = Core()
model = ie.read_model(model=model_xml_path, weights=model_xml_path.with_suffix(".bin"))
compiled_model = ie.compile_model(model=model, device_name=DEVICE)

input_key = compiled_model.input(0)
output_key = compiled_model.output(0)

network_input_shape = list(input_key.shape)
network_image_height, network_image_width = network_input_shape[2:]

Monodepth on Image

Load, resize and reshape input image

The input image is read with OpenCV, resized to network input size, and reshaped to (N,C,H,W) (N=number of images, C=number of channels, H=height, W=width).

IMAGE_FILE = "data/coco_bike.jpg"
image = load_image(path=IMAGE_FILE)

# resize to input shape for network
resized_image = cv2.resize(src=image, dsize=(network_image_height, network_image_width))

# reshape image to network input shape NCHW
input_image = np.expand_dims(np.transpose(resized_image, (2, 0, 1)), 0)

Do inference on image

Do the inference, convert the result to an image, and resize it to the original image shape

result = compiled_model([input_image])[output_key]

# convert network result of disparity map to an image that shows
# distance as colors
result_image = convert_result_to_image(result=result)

# resize back to original image shape. cv2.resize expects shape
# in (width, height), [::-1] reverses the (height, width) shape to match this
result_image = cv2.resize(result_image, image.shape[:2][::-1])

Display monodepth image

fig, ax = plt.subplots(1, 2, figsize=(20, 15))
ax[0].imshow(to_rgb(image))
ax[1].imshow(result_image);

Monodepth on Video

By default, only the first 100 frames are processed, in order to quickly check that everything works. Change NUM_FRAMES in the cell below to modify this. Set NUM_FRAMES to 0 to process the whole video.

Video Settings

# Video source: https://www.youtube.com/watch?v=fu1xcQdJRws (Public Domain)
VIDEO_FILE = "data/Coco Walking in Berkeley.mp4"
# Number of seconds of input video to process. Set to 0 to process
# the full video.
NUM_SECONDS = 4
# Set ADVANCE_FRAMES to 1 to process every frame from the input video
# Set ADVANCE_FRAMES to 2 to process every second frame. This reduces
# the time it takes to process the video
ADVANCE_FRAMES = 2
# Set SCALE_OUTPUT to reduce the size of the result video
# If SCALE_OUTPUT is 0.5, the width and height of the result video
# will be half the width and height of the input video
SCALE_OUTPUT = 0.5
# The format to use for video encoding. vp09 is slow,
# but it works on most systems.
# Try the THEO encoding if you have FFMPEG installed.
# FOURCC = cv2.VideoWriter_fourcc(*"THEO")
FOURCC = cv2.VideoWriter_fourcc(*"vp09")

# Create Path objects for the input video and the resulting video
output_directory = Path("output")
output_directory.mkdir(exist_ok=True)
result_video_path = output_directory / f"{Path(VIDEO_FILE).stem}_monodepth.mp4"

Load Video

Load video from VIDEO_FILE, set in the Video Settings cell above. Open the video to read the frame width and height and fps, and compute values for these properties for the monodepth video.

cap = cv2.VideoCapture(str(VIDEO_FILE))
ret, image = cap.read()
if not ret:
    raise ValueError(f"The video at {VIDEO_FILE} cannot be read.")
input_fps = cap.get(cv2.CAP_PROP_FPS)
input_video_frame_height, input_video_frame_width = image.shape[:2]

target_fps = input_fps / ADVANCE_FRAMES
target_frame_height = int(input_video_frame_height * SCALE_OUTPUT)
target_frame_width = int(input_video_frame_width * SCALE_OUTPUT)

cap.release()
print(
    f"The input video has a frame width of {input_video_frame_width}, "
    f"frame height of {input_video_frame_height} and runs at {input_fps:.2f} fps"
)
print(
    "The monodepth video will be scaled with a factor "
    f"{SCALE_OUTPUT}, have width {target_frame_width}, "
    f" height {target_frame_height}, and run at {target_fps:.2f} fps"
)

The input video has a frame width of 640, frame height of 360 and runs at 30.00 fps
The monodepth video will be scaled with a factor 0.5, have width 320,  height 180, and run at 15.00 fps

Do Inference on a Video and Create Monodepth Video

# Initialize variables
input_video_frame_nr = 0
start_time = time.perf_counter()
total_inference_duration = 0

# Open input video
cap = cv2.VideoCapture(str(VIDEO_FILE))

# Create result video
out_video = cv2.VideoWriter(
    str(result_video_path),
    FOURCC,
    target_fps,
    (target_frame_width * 2, target_frame_height),
)

num_frames = int(NUM_SECONDS * input_fps)
total_frames = cap.get(cv2.CAP_PROP_FRAME_COUNT) if num_frames == 0 else num_frames
progress_bar = ProgressBar(total=total_frames)
progress_bar.display()

try:
    while cap.isOpened():
        ret, image = cap.read()
        if not ret:
            cap.release()
            break

        if input_video_frame_nr >= total_frames:
            break

        # Only process every second frame
        # Prepare frame for inference
        # resize to input shape for network
        resized_image = cv2.resize(src=image, dsize=(network_image_height, network_image_width))
        # reshape image to network input shape NCHW
        input_image = np.expand_dims(np.transpose(resized_image, (2, 0, 1)), 0)

        # Do inference
        inference_start_time = time.perf_counter()
        result = compiled_model([input_image])[output_key]
        inference_stop_time = time.perf_counter()
        inference_duration = inference_stop_time - inference_start_time
        total_inference_duration += inference_duration

        if input_video_frame_nr % (10 * ADVANCE_FRAMES) == 0:
            clear_output(wait=True)
            progress_bar.display()
            # input_video_frame_nr // ADVANCE_FRAMES gives the number of
            # frames that have been processed by the network
            display(
                Pretty(
                    f"Processed frame {input_video_frame_nr // ADVANCE_FRAMES}"
                    f"/{total_frames // ADVANCE_FRAMES}. "
                    f"Inference time per frame: {inference_duration:.2f} seconds "
                    f"({1/inference_duration:.2f} FPS)"
                )
            )

        # Transform network result to RGB image
        result_frame = to_rgb(convert_result_to_image(result))
        # Resize image and result to target frame shape
        result_frame = cv2.resize(result_frame, (target_frame_width, target_frame_height))
        image = cv2.resize(image, (target_frame_width, target_frame_height))
        # Put image and result side by side
        stacked_frame = np.hstack((image, result_frame))
        # Save frame to video
        out_video.write(stacked_frame)

        input_video_frame_nr = input_video_frame_nr + ADVANCE_FRAMES
        cap.set(1, input_video_frame_nr)

        progress_bar.progress = input_video_frame_nr
        progress_bar.update()

except KeyboardInterrupt:
    print("Processing interrupted.")
finally:
    clear_output()
    processed_frames = num_frames // ADVANCE_FRAMES
    out_video.release()
    cap.release()
    end_time = time.perf_counter()
    duration = end_time - start_time

    print(
        f"Processed {processed_frames} frames in {duration:.2f} seconds. "
        f"Total FPS (including video processing): {processed_frames/duration:.2f}."
        f"Inference FPS: {processed_frames/total_inference_duration:.2f} "
    )
    print(f"Monodepth Video saved to '{str(result_video_path)}'.")

Processed 60 frames in 12.20 seconds. Total FPS (including video processing): 4.92.Inference FPS: 24.29
Monodepth Video saved to 'output/Coco Walking in Berkeley_monodepth.mp4'.

Display Monodepth Video

video = Video(result_video_path, width=800, embed=True)
if not result_video_path.exists():
    plt.imshow(stacked_frame)
    raise ValueError("OpenCV was unable to write the video file. Showing one video frame.")
else:
    print(f"Showing monodepth video saved at\n{result_video_path.resolve()}")
    print(
        "If you cannot see the video in your browser, please click on the "
        "following link to download the video "
    )
    video_link = FileLink(result_video_path)
    video_link.html_link_str = "<a href='%s' download>%s</a>"
    display(HTML(video_link._repr_html_()))
    display(video)

Showing monodepth video saved at
/home/runner/work/openvino_notebooks/openvino_notebooks/notebooks/201-vision-monodepth/output/Coco Walking in Berkeley_monodepth.mp4
If you cannot see the video in your browser, please click on the following link to download the video

output/Coco Walking in Berkeley_monodepth.mp4

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