[英]How to set a matrix region with opencv4nodejs
問題 :
在opencv4nodejs中設置矩陣區域的最快方法是什么?
問題 :
我將源圖像疊加到尺寸較小的數千個較大的目標圖像中。
在Python中,我將通過以下方式獲取/設置大小匹配的區域:
destination[y:y+h, x:x+w] = source[:,:]
但是我不確定如何在Javascript中執行此操作。
我嘗試了幾種方法,但是即使最快,也非常慢。
例如,我有:
將矩陣轉換為數組,循環行和列,設置目標像素大約需要12秒
let debug_overlay_start = new Date().valueOf();
let source_pixels = source_mat.getDataAsArray();
for (let row_index = 0, l_1 = source_pixels.length; row_index < l_1; row_index++) {
if(row_index + offset_y < 0) continue;
if(row_index + offset_y >= dest_mat.rows) continue;
let this_col = source_pixels[row_index];
for (let col_index = 0, l_2 = this_col.length; col_index < l_2; col_index++) {
if(col_index + offset_x < 0) continue;
if(col_index + offset_x >= dest_mat.cols) continue;
dest_mat.set(row_index + offset_y, col_index + offset_x, source_pixels[row_index][col_index]);
}
}
let debug_overlay_end = new Date().valueOf();
console.log(`overlay method took ${((debug_overlay_end - debug_overlay_start)/1000).toFixed(2)}`); // overlay method took 11.63
return dest_mat;
將它們都轉換為數組,遍歷行,拼接cols耗時82秒:
let debug_overlay_end = new Date().valueOf();
let source_pixels = source_mat.getDataAsArray();
let new_dest_mat = dest_mat.getDataAsArray();
for (let row_index = 0, l_1 = source_pixels.length; row_index < l_1; row_index++) {
if(row_index + offset_y < 0) continue;
if(row_index + offset_y >= dest_mat.rows) continue;
let this_col = source_pixels[row_index]; // entire column of source pixels
new_dest_mat[row_index + offset_y].splice(offset_x, this_col.length, ...this_col);
}
let debug_overlay_end = new Date().valueOf();
console.log(`overlay method took ${((debug_overlay_end - debug_overlay_start)/1000).toFixed(2)}`); // 82 seconds
return new cv.Mat(new_dest_mat, dest_mat.type);
替換區域根本不起作用,在沒有其他日志記錄的情況下引發了生命周期錯誤:
let debug_overlay_end = new Date().valueOf();
let area_to_replace = dest_mat.getRegion(new cv.Rect(x, y, source_mat.cols, source_mat.rows));
area_to_replace = source_mat.getRegion(new cv.Rect(0, 0, source_mat.cols, source_mat.rows)); // lifecycle error
console.log(`overlay method took ${((debug_overlay_end - debug_overlay_start)/1000).toFixed(2)}`);
return dest_mat;
到目前為止,使用setAt()
和atRaw()
最快是8秒:
let debug_overlay_start = new Date().valueOf();
for(let row_index = 0, row_length = source_mat.rows; row_index < row_length; row_index++){
if(row_index + offset_y < 0) continue;
if(row_index + offset_y >= dest_mat.rows) continue;
for(let col_index = 0, col_length = source_mat.cols; col_index < col_length; col_index++){
if(col_index + offset_x < 0) continue;
if(col_index + offset_x >= dest_mat.cols) continue;
dest_mat.set(row_index + offset_y, col_index + offset_x, source_mat.atRaw(row_index, col_index));
}
}
let debug_overlay_end = new Date().valueOf();
console.log(`overlay method took ${((debug_overlay_end - debug_overlay_start)/1000).toFixed(2)}`); // 8.09
return dest_mat;
我看了看文檔,很驚訝地看到這不是一個普通的用例。 節點/電子環境是否會減慢本應快速的運行速度?
使用緩沖區陣列設法減少到1.1秒。 不確定如何加快速度。
/**
* Places a source matrix onto a dest matrix.
* Note: This replaces pixels entirely, it doesn't merge transparency
* @param {cv.Mat} source_mat matrix being copied
* @param {cv.Mat} dest_mat matrix being pasted into
* @param {number} x horizontal offset of source image
* @param {number} y vertical offset of source image
*/
function overlayOnto(source_mat, dest_mat, x, y){
if(source_mat.channels != dest_mat.channels) throw new Error('src and dst channel counts must match');
let source_uint8 = new Uint8Array( source_mat.getData() ); // WARNING 4 CHANNELS
let dest_uint8 = new Uint8Array( dest_mat.getData() ); // WARNING 4 CHANNELS
let dest_width = dest_mat.cols;
let x_count = 0; // set counters
let y_count = 0; // set counters
let channel_count = source_mat.channels;
for (let i = 0; i < source_uint8.length; i += channel_count) { // WARNING 4 CHANNELS
let dest_x = x_count + x; // add offset
let dest_y = y_count + y; // add offset
if( !( (dest_x < 0 || dest_x > dest_mat.cols-1) || (dest_y < 0 || dest_y > dest_mat.rows-1) ) ){ // pixel does not fall outside of dest mat
// write into buffer array
let dest_i = (dest_x + dest_width * dest_y); // (x + w * h) to get x/y coord in single-dimension array
let dest_buffer_i = dest_i * channel_count;
if(channel_count >= 1) dest_uint8.fill(source_uint8[i+0], dest_buffer_i+0 , dest_buffer_i+0+1);
if(channel_count >= 2) dest_uint8.fill(source_uint8[i+1], dest_buffer_i+1 , dest_buffer_i+1+1);
if(channel_count >= 3) dest_uint8.fill(source_uint8[i+2], dest_buffer_i+2 , dest_buffer_i+2+1);
if(channel_count >= 4) dest_uint8.fill(source_uint8[i+3], dest_buffer_i+3 , dest_buffer_i+3+1);
}
x_count++; // increase col
x_count = x_count % source_mat.cols; // end of col? move to start
if(x_count == 0) y_count++; // started new col? increase row
}
return new cv.Mat(dest_uint8, dest_mat.rows, dest_mat.cols, dest_mat.type);
}
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