我正在使用某人的源代码来使用 AVCaptureSession 捕获图像。但是，我发现 CaptureSessionManager 的 previewLayer 是 shotter，然后是最终捕获的图像。
我发现结果图像的比例始终为 720x1280=9:16。现在我想将生成的图像裁剪为比例为 320:480 的 UIImage，这样它只会捕获在 previewLayer 中可见的部分。任何想法？非常感谢。
stackoverflow 中的相关问题（还没有好的答案）： Q1， Q2
源代码：
- (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];
}];
}
在进行更多研究和测试后进行编辑： AVCaptureSession 的属性“sessionPreset”具有以下常量，我没有检查每一个，但注意到大多数比例是 9:16 或 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;
在我的项目中，我还有全屏预览（帧大小为 320x480）： [[self previewLayer] setVideoGravity:AVLayerVideoGravityResizeAspectFill];
我是这样做的：以 9:16 的尺寸拍摄照片并将其裁剪为 320:480，这正是预览层的可见部分。它看起来很完美。
用于调整大小和裁剪以替换旧代码的代码是
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]];