2023年02月01日 更新
Colaboratoryで、ループ処理内のカメラ映像を使用する方法
どうも、クラゲジュニアです。
ColaboratoryでWEBカメラの映像を使用する場合、cv2.VideoCapture()を使用できない点や、
コードスニペット内にある Camera Capture ではループ処理を行えない等いくつか問題があります。
以下方法を用いれば、簡単にループ処理内のカメラ映像を使用することができます。
関数を定義
まず、以下関数を定義します。
from IPython.display import display, Javascript, Image
from google.colab.output import eval_js
from base64 import b64decode, b64encode
import PIL
import io
import html
# function to convert the JavaScript object into an OpenCV image
def js_to_image(js_reply):
"""
Params:
js_reply: JavaScript object containing image from webcam
Returns:
img: OpenCV BGR image
"""
# decode base64 image
image_bytes = b64decode(js_reply.split(',')[1])
# convert bytes to numpy array
jpg_as_np = np.frombuffer(image_bytes, dtype=np.uint8)
# decode numpy array into OpenCV BGR image
img = cv2.imdecode(jpg_as_np, flags=1)
return img
# function to convert OpenCV Rectangle bounding box image into base64 byte string to be overlayed on video stream
def bbox_to_bytes(bbox_array):
"""
Params:
bbox_array: Numpy array (pixels) containing rectangle to overlay on video stream.
Returns:
bytes: Base64 image byte string
"""
# convert array into PIL image
bbox_PIL = PIL.Image.fromarray(bbox_array, 'RGBA')
iobuf = io.BytesIO()
# format bbox into png for return
bbox_PIL.save(iobuf, format='png')
# format return string
bbox_bytes = 'data:image/png;base64,{}'.format((str(b64encode(iobuf.getvalue()), 'utf-8')))
return bbox_bytes
# JavaScript to properly create our live video stream using our webcam as input
def video_stream():
js = Javascript('''
var video;
var div = null;
var stream;
var captureCanvas;
var imgElement;
var labelElement;
var pendingResolve = null;
var shutdown = false;
function removeDom() {
stream.getVideoTracks()[0].stop();
video.remove();
div.remove();
video = null;
div = null;
stream = null;
imgElement = null;
captureCanvas = null;
labelElement = null;
}
function onAnimationFrame() {
if (!shutdown) {
window.requestAnimationFrame(onAnimationFrame);
}
if (pendingResolve) {
var result = "";
if (!shutdown) {
captureCanvas.getContext('2d').drawImage(video, 0, 0, 640, 480);
result = captureCanvas.toDataURL('image/jpeg', 0.8)
}
var lp = pendingResolve;
pendingResolve = null;
lp(result);
}
}
async function createDom() {
if (div !== null) {
return stream;
}
div = document.createElement('div');
div.style.border = '2px solid black';
div.style.padding = '3px';
div.style.width = '100%';
div.style.maxWidth = '600px';
document.body.appendChild(div);
const modelOut = document.createElement('div');
modelOut.innerHTML = "<span>Status:</span>";
labelElement = document.createElement('span');
labelElement.innerText = 'No data';
labelElement.style.fontWeight = 'bold';
modelOut.appendChild(labelElement);
div.appendChild(modelOut);
video = document.createElement('video');
video.style.display = 'block';
video.width = div.clientWidth - 6;
video.setAttribute('playsinline', '');
video.onclick = () => { shutdown = true; };
stream = await navigator.mediaDevices.getUserMedia(
{video: { facingMode: "environment"}});
div.appendChild(video);
imgElement = document.createElement('img');
imgElement.style.position = 'absolute';
imgElement.style.zIndex = 1;
imgElement.onclick = () => { shutdown = true; };
div.appendChild(imgElement);
const instruction = document.createElement('div');
instruction.innerHTML =
'<span style="color: red; font-weight: bold;">' +
'When finished, click here or on the video to stop this demo</span>';
div.appendChild(instruction);
instruction.onclick = () => { shutdown = true; };
video.srcObject = stream;
await video.play();
captureCanvas = document.createElement('canvas');
captureCanvas.width = 640; //video.videoWidth;
captureCanvas.height = 480; //video.videoHeight;
window.requestAnimationFrame(onAnimationFrame);
return stream;
}
async function stream_frame(label, imgData) {
if (shutdown) {
removeDom();
shutdown = false;
return '';
}
var preCreate = Date.now();
stream = await createDom();
var preShow = Date.now();
if (label != "") {
labelElement.innerHTML = label;
}
if (imgData != "") {
var videoRect = video.getClientRects()[0];
imgElement.style.top = videoRect.top + "px";
imgElement.style.left = videoRect.left + "px";
imgElement.style.width = videoRect.width + "px";
imgElement.style.height = videoRect.height + "px";
imgElement.src = imgData;
}
var preCapture = Date.now();
var result = await new Promise(function(resolve, reject) {
pendingResolve = resolve;
});
shutdown = false;
return {'create': preShow - preCreate,
'show': preCapture - preShow,
'capture': Date.now() - preCapture,
'img': result};
}
''')
display(js)
def video_frame(label, bbox):
data = eval_js('stream_frame("{}", "{}")'.format(label, bbox))
return data関数の呼び出し
例として、カメラ映像の左上にHELLOと表示させています。
import cv2
import numpy as np
#（カメラ動画処理）
bbox = ""
video_stream()
label_html = "Capturing..."
# メインループ
while True:
# js_replyにカメラ映像のデータが入っている（カメラ動画処理）
js_reply = video_frame(label_html, bbox)
if not js_reply:
break
# frame に画像データが入っている（カメラ動画処理）
frame = js_to_image(js_reply["img"])
#（カメラ動画処理）
bbox_array = np.zeros([480,640,4], dtype=np.uint8)
# 文字列描画
bbox_array = cv2.putText(bbox_array, "HELLO", (10, 30), cv2.FONT_HERSHEY_SIMPLEX, 1, (240, 180, 0), 2)
#（カメラ動画処理）
bbox_array[:,:,3] = (bbox_array.max(axis = 2) > 0 ).astype(int) * 255
bbox_bytes = bbox_to_bytes(bbox_array)
bbox = bbox_bytes以上です。