加快保存图像 - iOS

Question

我正在研究更多的迷你项目,后来将其纳入一个新项目.它基本上是一个测试单元.

我正在做的是创建一个AVCaptureSession然后创建一个方法OutputSampleBufferDelegate.在方法中,我将转换sampleBuffer为a UIImage并保存UIImage.当我在iPhone 4上运行应用程序时,它每秒只能保存2-3张图像.必须有一种更有效的方法来保存图像.

有人可以帮助我加快速度吗？

谢谢!

很多代码来自这里

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{   
    UIImage *resultUIImage = [self imageFromSampleBuffer:sampleBuffer];

    NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(resultUIImage)];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *path = [paths objectAtIndex:0];

    CMTime frameTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);

    NSString *filename =  [NSString stringWithFormat:@"%f.png", CMTimeGetSeconds(frameTime)];

    NSString *finalPath = [path stringByAppendingString:filename];

    [imageData writeToFile:finalPath atomically:YES];
}

// Create a UIImage from sample buffer data
- (UIImage *)imageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer 
{
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0); 

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer); 

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context); 
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(context); 
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return image;
}

Answer 1

使用此代码,我可以将图像保存时间缩短到0.1秒.

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
       fromConnection:(AVCaptureConnection *)connection 
{  

    double frameTime = CFAbsoluteTimeGetCurrent();
    UIImage *resultUIImage = [self imageFromSampleBuffer:sampleBuffer];

    // takes freaking forever to do.
    double pre = CFAbsoluteTimeGetCurrent();
    NSData *imageData = UIImageJPEGRepresentation(resultUIImage, 0.9);
    NSLog(@"It took to write the file:%f",CFAbsoluteTimeGetCurrent()-pre);

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory
                                                         ,NSUserDomainMask
                                                         , YES);
    NSString *path = [paths objectAtIndex:0];
    NSString *filename =  [NSString stringWithFormat:@"%f.png", frameTime];
    NSString *finalPath = [path stringByAppendingString:filename];
    [imageData writeToFile:finalPath atomically:YES];
}

Answer 2

如果您在第一种方法中注释掉以下行，请看看您可以生成多少图像：

[imageData writeToFile:finalPath atomically:YES];

我这么说的原因是您将花费大量时间将该映像写入磁盘。看看它如何在不将图像写入磁盘的情况下执行会很有趣。至少这样你就会知道所有的时间是花在实际创建图像上还是存储图像上。或者你可以像另一张海报提到的那样做，并使用 Instruments 来计算你在每种方法中的时间。

如果事实证明将图像写入磁盘花费的时间太长，那么我建议尝试实现一种缓存机制，将图像缓存在内存中并稍后将它们写入磁盘。

尝试在后台线程上调用 writeToFile:atomically: 也可能会有所帮助。