SamB SamB - 6 months ago 57
iOS Question

Speed up saving image - iOS

I am working on more of mini-project that will be later included into a new project. It is basically a test unit.

What I am doing is creating an

and then creating a method for
. In the method, I convert the
into a
and save the
. When I run the application on my iPhone 4 it can only save 2-3 images per second. There must be a more efficient way to save the image.

Can someone help me speed it up?


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

// Free up the context and color space

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

// Release the Quartz image

return image;


Using this code I can get the time it saves the image down to 0.1 sec.

- (void)captureOutput:(AVCaptureOutput *)captureOutput
       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
                                                         , YES);
    NSString *path = [paths objectAtIndex:0];
    NSString *filename =  [NSString stringWithFormat:@"%f.png", frameTime];
    NSString *finalPath = [path stringByAppendingString:filename];
    [imageData writeToFile:finalPath atomically:YES];