我正在尝试做的是:
我所做的与此处描述的大致相同:
https://answers.opencv.org/question/222994/how-to-pass-image-data-from-javascript-to-opencv-c-webassembly/
这是javascript部分(给定链接的冗长部分):
var openFile = function (e) {
const fileReader = new FileReader();
fileReader.onload = (event) => {
const uint8Arr = new Uint8Array(event.target.result);
passToWasm(uint8Arr);
};
fileReader.readAsArrayBuffer(e.target.files[0]);
};
function passToWasm(uint8ArrData) {
// copying the uint8ArrData to the heap
const numBytes = uint8ArrData.length * uint8ArrData.BYTES_PER_ELEMENT;
const dataPtr = Module._malloc(numBytes);
const dataOnHeap = new Uint8Array(Module.HEAPU8.buffer, dataPtr, numBytes);
dataOnHeap.set(uint8ArrData);
// calling the Wasm function
console.log(dataOnHeap.byteOffset);
const res = Module._image_input(dataOnHeap.byteOffset, uint8ArrData.length);
Module._free(dataPtr);
}
这是C++部分(几乎逐字记录):
int image_input(int offset, size_t size) //query image input
{
uint8_t* pos;
pos = reinterpret_castw<uint8_t*>(offset);
cv::Mat raw_data = cv::Mat(1, size, CV_8UC1, pos);
cout << raw_data << endl;
img_object = cv::imdecode(raw_data, cv::IMREAD_GRAYSCALE);
cout << img_object << endl;
}
当我用一些jpg图像进行测试时,C++部分的
raw_data
和JS部分的uint8ArrData
包含相同的信息:这是15253个数字的列表,例如[255, 216, 255, 224, ..., 184, 227, 255, 217]
现在,线
img_object = cv::imdecode(raw_data, cv::IMREAD_GRAYSCALE);
返回一个空矩阵
[]
。我做错了什么?
我是否必须在JS端进行一些预处理?
最佳答案
如提供的链接中所述,解决方案是使用 Canvas 并将像素列表(以4x480x640数字为例)发送到C++。
在JS方面,
function sendCanvas(canvas, baseImage) {
const context = canvas.getContext('2d');
context.drawImage(baseImage, 0, 0, baseImage.width, baseImage.height);
const { width } = canvas;
const { height } = canvas;
const imgData = context.getImageData(0, 0, canvas.width, canvas.height);
const uint8ArrData = new Uint8Array(imgData.data);
// pass the width and height too !!
passToWasm(uint8ArrData, width, height);
}
const baseImage = new Image();
baseImage.src = 'test.jpg';
baseImage.onload = () => sendCanvas(canvas, baseImage);
您必须使函数
passToWasm
适应其他两个参数(宽度和高度),并将它们传递给C++调用。然后在C++方面,直接使用以下信息将图像创建为
cv::Mat
:void image_input(int offset, size_t size, int width, int height) {
// People in the doc do not need this cast trick. Why ???
uint8_t *pos;
pos = reinterpret_cast<uint8_t *>(offset);
auto cv_image = cv::Mat(width, height, CV_8UC4, pos);
}
矩阵
cv_image
已准备好进行操作。
关于javascript - cv::imcode将图像从JS解码到C++(opencv,emscripten),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/61477860/