在裁剪之前調整UIImage或CIImage的大小，拉伸圖像？

Question

好吧，我已經試過了我可以找到的所有例子，可悲的是，其中大部分都是從2008年到2009年，而iOS5似乎有很大的不同。我只是想調整大小和圖像，以便短邊是我指定的大小，並保持不變。

我使用AVFoundation從相機抓取圖像，我通過UIImage將其轉換爲CIImage，以便在轉換回UIImage進行保存之前應用濾鏡和小提琴。

- (void) startCamera { 

session = [[AVCaptureSession alloc] init]; 
session.sessionPreset = AVCaptureSessionPresetPhoto; 

AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session]; 
captureVideoPreviewLayer.frame = _cameraView.bounds; 
[_cameraView.layer addSublayer:captureVideoPreviewLayer]; 
captureVideoPreviewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill; 

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo]; 
NSError *error = nil; 

AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error]; 
if (!input) { 
    //no cam, handle error - need to put up a nice happy note here 
    NSLog(@"ERROR: %@", error); 
} 

[session addInput:input]; 

stillImage = [[AVCaptureStillImageOutput alloc] init]; 
NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys:AVVideoCodecJPEG , AVVideoCodecKey, nil]; 
[stillImage setOutputSettings:outputSettings]; 

[session addOutput:stillImage]; 
[session startRunning]; 
} 

- (IBAction) _cameraButtonPress:(id)sender { 

AVCaptureConnection *videoConnection = nil; 
for (AVCaptureConnection *connection in stillImage.connections) 
{ 
    for (AVCaptureInputPort *port in [connection inputPorts]) 
    { 
     if ([[port mediaType] isEqual:AVMediaTypeVideo]) 
     { 
      videoConnection = connection; 
      break; 
     } 
    } 
    if (videoConnection) { 
     break; 
    } 
} 

[stillImage captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:^(CMSampleBufferRef imageSampleBuffer, NSError *error) { 

    NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer]; 
    UIImage *startImage = [[UIImage alloc] initWithData:imageData]; 

    //resizing of image to take place before anything else 
    UIImage *image = [startImage imageScaledToFitSize:_exportSSize]; //resizes to the size given in the prefs 

    //change the context to render using cpu, so on app exit renders get completed 
    context = [CIContext contextWithOptions: 
       [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] 
              forKey:kCIContextUseSoftwareRenderer]]; 

    //set up the saving library 
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init]; 

    //create a new ciimage 
    CIImage *greyImage = [[CIImage alloc] initWithCGImage:[image CGImage]]; 

    //create a CIMonochrome filter 
    desaturate = [CIFilter filterWithName:@"CIColorMonochrome" keysAndValues:kCIInputImageKey, greyImage, @"inputIntensity", [NSNumber numberWithFloat:0.00], nil]; 

    //[crop setValue:ciImage forKey:@"inputImage"]; 
    //[crop setValue:[CIVector vectorWithX:0.0f Y:0.0f Z:_exportSize W:_exportSize] forKey:@"inputRectangle"]; 

    CIImage *croppedColourImage = [desaturate valueForKey:@"outputImage"]; 
    //convert it to a cgimage for saving 
    CGImageRef cropColourImage = [context createCGImage:croppedColourImage fromRect:[croppedColourImage extent]]; 

    //saving of the images   
    [library writeImageToSavedPhotosAlbum:cropColourImage metadata:[croppedColourImage properties] completionBlock:^(NSURL *assetURL, NSError *error){ 
    if (error) { 
     NSLog(@"ERROR in image save: %@", error); 
    } else 
    { 
     NSLog(@"SUCCESS in image save"); 
     //in here we'll put a nice animation or something 
     CGImageRelease(cropColourImage); 
    } 

    }]; 
}]; 
} 

此代碼是測試代碼，所以會有各種各樣的嘗試，爲此道歉。

我有使用馬特Gemmell代碼here

最接近但是，無論我怎麼努力，總是綿延的圖像。我想調整圖像大小，然後將其裁剪爲512像素平方。如果我只是做一個CICrop過濾器，它需要左上512像素，所以我失去了很多圖像（抓取高分辨率的照片，因爲後來我還想導出1800x1800圖像）。我的想法是先調整圖像大小，然後裁剪。但是無論我做什麼，圖像都會變得很緊張。

所以我的問題是，有沒有適當的建議公認的方式來調整大小和圖像在iOS5 +？

謝謝。

Answer 1

我發現這樣做的一種方式：

UIGraphicsBeginImageContext(newSize); 

[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)]; 

UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext(); 

UIGraphicsEndImageContext();