Question

我正在研究更多小型项目，后来将其纳入新项目。它基本上是一个测试单元。

我正在做的是创建AVCaptureSession，然后为OutputSampleBufferDelegate创建方法。在该方法中，我将sampleBuffer转换为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！

lots of the code is from here

- (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，我可以节省将图像保存到0.1秒的时间。

- (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，可以查看可以生成的图像数量：

[imageData writeToFile:finalPath atomically:YES];

我说的原因是你要花很多时间把这个图像写到磁盘上。看看如何在不将图像写入磁盘的情况下执行它将会很有趣。至少通过这种方式，您将知道是否所有时间都用于实际创建图像而不是存储图像。或者你可以像另一张提到的海报那样做，并使用仪器来计算你在每种方法中的使用时间。

如果事实证明将图像写入磁盘的时间太长，那么我建议尝试实现一种缓存机制，将内存中的图像缓存并稍后将其写入磁盘。

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

加快保存图像 - iOS

2 个答案: