SamB SamB - 3 months ago 41
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

AVCaptureSession
and then creating a method for
OutputSampleBufferDelegate
. In the method, I convert the
sampleBuffer
into a
UIImage
and save the
UIImage
. 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?

Thanks!

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

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

- (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];
}
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