Capture still UIImage without compression (from CMSampleBufferRef)? - ios

Question

I need to obtain the UIImage from uncompressed image data from CMSampleBufferRef. I'm using the code:
captureStillImageOutput captureStillImageAsynchronouslyFromConnection:connection
completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error)
{
// that famous function from Apple docs found on a lot of websites
// does NOT work for still images
UIImage *capturedImage = [self imageFromSampleBuffer:imageSampleBuffer];
}
http://developer.apple.com/library/ios/#qa/qa1702/_index.html is a link to imageFromSampleBuffer function.
But it does not work properly. :(
There is a jpegStillImageNSDataRepresentation:imageSampleBuffer method, but it gives the compressed data (well, because JPEG).
How can I get UIImage created with the most raw non-compressed data after capturing Still Image?
Maybe, I should specify some settings to video output? I'm currently using those:
captureStillImageOutput = [[AVCaptureStillImageOutput alloc] init];
captureStillImageOutput.outputSettings = #{ (id)kCVPixelBufferPixelFormatTypeKey : #(kCVPixelFormatType_32BGRA) };
I've noticed, that output has a default value for AVVideoCodecKey, which is AVVideoCodecJPEG. Can it be avoided in any way, or does it even matter when capturing still image?
I found something there: Raw image data from camera like "645 PRO" , but I need just a UIImage, without using OpenCV or OGLES or other 3rd party.

Answer 1

The method imageFromSampleBuffer does work in fact I'm using a changed version of it, but if I remember correctly you need to set the outputSettings right. I think you need to set the key as kCVPixelBufferPixelFormatTypeKey and the value as kCVPixelFormatType_32BGRA.
So for example:
NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA];
NSDictionary* outputSettings = [NSDictionary dictionaryWithObject:value forKey:key];
[newStillImageOutput setOutputSettings:outputSettings];
EDIT
I am using those settings to take stillImages not video.
Is your sessionPreset AVCaptureSessionPresetPhoto? There may be problems with that
AVCaptureSession *newCaptureSession = [[AVCaptureSession alloc] init];
[newCaptureSession setSessionPreset:AVCaptureSessionPresetPhoto];
EDIT 2
The part about saving it to UIImage is identical with the one from the documentation. That's the reason I was asking for other origins of the problem, but I guess that was just grasping for straws.
There is another way I know of, but that requires OpenCV.
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer, 0);
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);
}
I guess that is of no help to you, sorry. I don't know enough to think of other origins for your problem.

Answer 2

Here's a more efficient way:
UIImage *image = [UIImage imageWithData:[self imageToBuffer:sampleBuffer]];
- (NSData *) imageToBuffer:(CMSampleBufferRef)source {
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(source);
CVPixelBufferLockBaseAddress(imageBuffer,0);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
void *src_buff = CVPixelBufferGetBaseAddress(imageBuffer);
NSData *data = [NSData dataWithBytes:src_buff length:bytesPerRow * height];
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
return data;
}