iPhone image ratio captured from AVCaptureSession - iphone

Question

I am using somebody's source code for capturing image with AVCaptureSession. However,I found that CaptureSessionManager's previewLayer is shotter then the final captured image.
I found that the resulted image is always with ratio 720x1280=9:16. Now I want to crop the resulted image to an UIImage with ratio 320:480 so that it will only capture the portion visible in previewLayer. Any Idea? Thanks a lot.
Relevant Questions in stackoverflow(NO good answer yet):
Q1,
Q2
Source Code:
- (id)init {
if ((self = [super init])) {
[self setCaptureSession:[[[AVCaptureSession alloc] init] autorelease]];
}
return self;
}
- (void)addVideoPreviewLayer {
[self setPreviewLayer:[[[AVCaptureVideoPreviewLayer alloc] initWithSession:[self captureSession]] autorelease]];
[[self previewLayer] setVideoGravity:AVLayerVideoGravityResizeAspectFill];
}
- (void)addVideoInput {
AVCaptureDevice *videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
if (videoDevice) {
NSError *error;
if ([videoDevice isFocusModeSupported:AVCaptureFocusModeContinuousAutoFocus] && [videoDevice lockForConfiguration:&error]) {
[videoDevice setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
[videoDevice unlockForConfiguration];
}
AVCaptureDeviceInput *videoIn = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
if (!error) {
if ([[self captureSession] canAddInput:videoIn])
[[self captureSession] addInput:videoIn];
else
NSLog(#"Couldn't add video input");
}
else
NSLog(#"Couldn't create video input");
}
else
NSLog(#"Couldn't create video capture device");
}
- (void)addStillImageOutput
{
[self setStillImageOutput:[[[AVCaptureStillImageOutput alloc] init] autorelease]];
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG,AVVideoCodecKey,nil];
[[self stillImageOutput] setOutputSettings:outputSettings];
AVCaptureConnection *videoConnection = nil;
for (AVCaptureConnection *connection in [[self stillImageOutput] connections]) {
for (AVCaptureInputPort *port in [connection inputPorts]) {
if ([[port mediaType] isEqual:AVMediaTypeVideo] ) {
videoConnection = connection;
break;
}
}
if (videoConnection) {
break;
}
}
[[self captureSession] addOutput:[self stillImageOutput]];
}
- (void)captureStillImage
{
AVCaptureConnection *videoConnection = nil;
for (AVCaptureConnection *connection in [[self stillImageOutput] connections]) {
for (AVCaptureInputPort *port in [connection inputPorts]) {
if ([[port mediaType] isEqual:AVMediaTypeVideo]) {
videoConnection = connection;
break;
}
}
if (videoConnection) {
break;
}
}
NSLog(#"about to request a capture from: %#", [self stillImageOutput]);
[[self stillImageOutput] captureStillImageAsynchronouslyFromConnection:videoConnection
completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) {
CFDictionaryRef exifAttachments = CMGetAttachment(imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);
if (exifAttachments) {
NSLog(#"attachements: %#", exifAttachments);
} else {
NSLog(#"no attachments");
}
NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
UIImage *image = [[UIImage alloc] initWithData:imageData];
[self setStillImage:image];
[image release];
[[NSNotificationCenter defaultCenter] postNotificationName:kImageCapturedSuccessfully object:nil];
}];
}
Edit after doing some more research and testing:
AVCaptureSession's property "sessionPreset" has the following constants, I haven't checked each one of them, but noted that most of them ratio is either 9:16, or 3:4,
NSString *const AVCaptureSessionPresetPhoto;
NSString *const AVCaptureSessionPresetHigh;
NSString *const AVCaptureSessionPresetMedium;
NSString *const AVCaptureSessionPresetLow;
NSString *const AVCaptureSessionPreset352x288;
NSString *const AVCaptureSessionPreset640x480;
NSString *const AVCaptureSessionPresetiFrame960x540;
NSString *const AVCaptureSessionPreset1280x720;
NSString *const AVCaptureSessionPresetiFrame1280x720;
In My project, I have the fullscreen preview(frame size is 320x480)
also: [[self previewLayer] setVideoGravity:AVLayerVideoGravityResizeAspectFill];
I have done it in this way: take the photo in size 9:16 and crop it to 320:480, exactly the visible part of the previewlayer. It looks perfect.
The piece of code for resizing and croping to replace with old code is
NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
UIImage *image = [UIImage imageWithData:imageData];
UIImage *scaledimage=[ImageHelper scaleAndRotateImage:image];
//going to crop the image 9:16 to 2:3;with Width fixed
float width=scaledimage.size.width;
float height=scaledimage.size.height;
float top_adjust=(height-width*3/2.0)/2.0;
[self setStillImage:[scaledimage croppedImage:rectToCrop]];

Answer 1

iPhone's camera is natively 4:3. The 16:9 images you get are already cropped from 4:3. Cropping those 16:9 images again to 4:3 is not what you want. Instead get the native 4:3 images from iPhone's camera by setting self.captureSession.sessionPreset = AVCaptureSessionPresetPhoto (before adding any inputs/outputs to the session).