Opencv imshow with waitKey too slow on Mac OS X 10.10.2 (using C ++)

Question

I use opencv C ++ on Mac OS X 10.10.2 to process video frames and display them. Imshow performance with waitKey for displaying video is very slow.

I have the following code that correctly displays grayscale frames (1920x1080), except that it runs about 10 times too slowly (i.e. 2 to 3 frames per second instead of 30 frames per second).

          cv::Mat framebuf[TEST_COUNT];

    //--- Code here to allocate and fill the frame buffer with about 4 seconds of video. This part works correctly.

        //--- This loop runs too slow by factor of approximately 10x
    for (int f = 0; f < TEST_COUNT; f++)
    {
        cv::imshow(windowName, framebuf[f]);
        cv::waitKey(33);
    }

Can anyone suggest how to get real-time or near-real-time performance from opencv imshow ()? I saw a lot of posts saying that they display video in real time or even faster than in real time, so I'm not sure what I'm doing wrong. Any help would be greatly appreciated.

Answer 1

I could be wrong, but for me the problem is not in the code, but in the os / configuration. I wrote a little test:

import cv2
import numpy as np
from random import randrange
img = np.zeros((1920, 1080), dtype = np.uint8)
counter = 0
while counter < 1000:
    cv2.line(img, (randrange(0, 1920), randrange(0, 1080)), (randrange(0, 1920), randrange(0, 1080)), (randrange(0, 255)))
    cv2.imshow('test', img)
    temp = cv2.waitKey(1)
    counter += 1
    print counter

(Core 2 Duo 2,6Ghz x64, 8gb ram, ssd) 30 . , , , - /opencv/etc. OpenCV 2.4.x Mac OS X ( 10.9, ), . OpenCV - , . OpenCV, brew - brew install opencv --with-tbb --with-python --with-ffpmeg ( - - brew options opencv) . brew opencv tbb ( , ), - python, - ffmpeg ( ..).

Answer 2

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Answer 3

, . MyWindow.m MyWindow.h .

MyWindow.h

#ifndef MY_WINDOW_H
#define MY_WINDOW_H

#ifdef __cplusplus
extern "C" {
#endif
    void* createNSWindow(int x, int y, int w, int h);
    void renderNSWindow(void* inwindow, void* data, int w, int h, int c);
    void processNSEvent();
#ifdef __cplusplus
}
#endif

#endif

, main.cpp, waitKey

#include "MyWindow.h"

// need create a cv window and do nothing
cv::namedWindow("xxx", 1);

// create window
void* w = createNSWindow(0, 0, 0, 0);

// frame image
cv::Mat frameImage;

// render loop
renderNSWindow(w, frameImage.data, frameImage.cols, frameImage.rows, frameImage.channels());

// need waitKey to display window
processNSEvent();

MyWindow.m "MyWindow.h"

#import <Cocoa/Cocoa.h>

@interface MyWindow : NSWindow
@property(nonatomic, strong) NSImageView *imgv;
@end

@implementation MyWindow
@end


static NSImage* _createNSImage(void* data, int w, int h, int c);

void* createNSWindow(int x, int y, int w, int h) {

    NSRect screenFrame = [[NSScreen mainScreen] frame];
    NSRect frame = NSMakeRect(x, y, w, h);
    if (w == 0 || h == 0) {
        frame = screenFrame;
    }

    MyWindow* window  = [[MyWindow alloc] initWithContentRect:frame
                                                    styleMask:NSWindowStyleMaskBorderless
                                                      backing:NSBackingStoreBuffered
                                                        defer:NO] ;


    //_initApp(window);

    [window makeKeyAndOrderFront:NSApp];
    window.titleVisibility = TRUE;
    window.styleMask = NSWindowStyleMaskResizable | NSWindowStyleMaskTitled |NSWindowStyleMaskFullSizeContentView;

    window.imgv = [[NSImageView alloc] initWithFrame:NSMakeRect(0, 0, frame.size.width, frame.size.height)];
    [window.contentView addSubview:window.imgv];


    return (void*)CFBridgingRetain(window);
}


static NSImage* _createNSImage(void* data, int w, int h, int c) {

    size_t bufferLength = w * h * c;

    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, data, bufferLength, NULL);
    size_t bitsPerComponent = 8;
    size_t bitsPerPixel = c * bitsPerComponent;
    size_t bytesPerRow = c * w;
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast;
    if (c < 4) {
        bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaNone;
        unsigned char* buf = data;
        for(int i = 0; i < w*h; i++) {
            unsigned char temp = buf[i*c];
            buf[i*c] = buf[i*c+c-1];
            buf[i*c+c-1] = temp;
        }
    }
    CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

    CGImageRef iref = CGImageCreate(w,
                                    h,
                                    bitsPerComponent,
                                    bitsPerPixel,
                                    bytesPerRow,
                                    colorSpaceRef,
                                    bitmapInfo,
                                    provider,   // data provider
                                    NULL,       // decode
                                    YES,        // should interpolate
                                    renderingIntent);

    NSImage* image = [[NSImage alloc] initWithCGImage:iref size:NSMakeSize(w, h)];
    return image;
}

void renderNSWindow(void* inwindow, void* data, int w, int h, int c) {
    MyWindow* window = (__bridge MyWindow*)inwindow;

    window.imgv.image = _createNSImage(data, w, h, c);

}

void processNSEvent() {
    for (;;)
    {
        NSEvent* event = [NSApp nextEventMatchingMask:NSEventMaskAny
                                            untilDate:[NSDate distantPast]
                                               inMode:NSDefaultRunLoopMode
                                              dequeue:YES];
        if (event == nil)
            break;

        [NSApp sendEvent:event];
    }
}

, waitKey 20 , OpenCV . processNSEvent waitKey, 10 .

:

#include <iostream>
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <dispatch/dispatch.h>
#include "MyWindow.h"


using namespace std;
using namespace cv;


int opencvfunc(int argc, const char *argv[]);
bool newFrame = false;
cv::Mat back_frame;

int main(int argc, const char * argv[]) {
    cv::namedWindow("render", 1);

    void* w = createNSWindow(0, 0, 0, 0);

    dispatch_queue_t opencvq = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
    dispatch_async(opencvq, ^{
        opencvfunc(argc, argv);
    });


    while(true) {
        usleep(3*1000);
        if(newFrame) {
            std::chrono::system_clock::time_point starttime = std::chrono::system_clock::now();
            renderNSWindow(w, back_frame.data, back_frame.cols, back_frame.rows, back_frame.channels());
            newFrame = false;
            //auto key = cv::waitKey(1);
            //if (key == 'q') {
            //    break;
            //}
            processNSEvent();
            std::chrono::system_clock::time_point endtime = std::chrono::system_clock::now();
            std::cout << "imshow:" << std::chrono::duration_cast<std::chrono::duration<double>>(endtime-starttime).count()*1000 << std::endl;
        }
    }

    return 0;
}

int opencvfunc(int argc, const char *argv[]) {

    cv::VideoCapture cap;
    cap.open(0);
    if (!cap.isOpened()) {
        std::cout << "Couldn't open camera 0." << endl;
        return EXIT_FAILURE;
    }

    Mat frame, unmodified_frame;

    for (;;) {

        cap >> frame; // get a new frame from camera
        if (frame.empty()) { // stop if we're at the end of the video
            break;
        }


        //unmodified_frame = frame.clone();

        // ...

        back_frame = frame.clone();
        newFrame = true;
    }

    return EXIT_SUCCESS;
}