iphone - iOS:裁剪从带有叠加层的 UIImagePickerController 相机抓取的静止图像

Question

我是 iOS 的新手，过去一周我一直在为此苦苦挣扎，在网上四处寻找教程，例如:Dealing with Exif Images , Resizing images ，以及更多关于 StackOverflow 的随机问题。从这些，我认为>=iOS 4.0，所有从相机拍摄的图像都包含基于EXIF的旋转信息。

什么不起作用:尝试不同的图像裁剪技术后，我最终得到的只是在一些随机角裁剪图像，而且生成的图像似乎被放大了:(当我使用来自互联网的 png 图像(不包含 EXIF 数据)，裁剪工作正常。我的意思是随机角 - 图像最终被裁剪在右上角/顶部 -向左并放大。

我想要完成的事情:
我正在尝试从顶部裁剪图像 100 px，从底部裁剪 100 px。本质上，我使用了两个覆盖条 - 1 个在顶部，1 个在底部，CGRect(0.0, 0.0, SCREEN_WIDTH, 100.0) [a 100.0 px 高 strip 在顶部] 和另一个 CGRect(0.0, SCREEN_HEIGHT - 100, SCREEN_WIDTH, 100.0) [另一个 100 px strip 在底部]。我需要在这两个 strip 之间获取图像:我假设图像的高度为:SCREEN_HEIGHT - 200.0。

为带覆盖的相机显示 UIImagePickerController:

    //SCREEN_HEIGHT = 480 and SCREEN_WIDTH = 320
    UIImagePickerController *imagePicker = [[UIImagePickerController alloc] init];

    if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera] == NO) 
    {
        NSLog(@"Camera not available");
        return;
    }

    imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
    imagePicker.delegate = self;
    imagePicker.allowsEditing = NO;


    // Hide the controls
    imagePicker.showsCameraControls = NO;
    imagePicker.navigationBarHidden = YES;

    // Make camera view full screen
    imagePicker.wantsFullScreenLayout = YES;
    //imagePicker.cameraViewTransform = CGAffineTransformScale(imagePicker.cameraViewTransform, CAMERA_TRANSFORM_X, CAMERA_TRANSFORM_Y);


    //Overlay
    //OverlayView is a plain UIView with the CGRects mentioned in the question.
    OverlayView *overlay = [[OverlayView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT)]; 
    [overlay initOverlay:self];
    imagePicker.cameraOverlayView = overlay;
    [self presentModalViewController:imagePicker animated:YES];

根据 EXIF imageOrientation 属性旋转图像并裁剪的代码

- (UIImage *) cropImage: (UIImage *) originalImage 
{

    CGRect cropRect = CGRectMake(0, 100.0, SCREEN_WIDTH, SCREEN_HEIGHT - 100);

    CGRect transformedRect = [self TransformCGRectForUIImageOrientation:cropRect :originalImage.imageOrientation :originalImage.size];

    CGImageRef resultImageRef = CGImageCreateWithImageInRect(originalImage.CGImage, transformedRect);

    UIImage *newImage = [[[UIImage alloc] initWithCGImage:resultImageRef scale:1.0 orientation:originalImage.imageOrientation] autorelease];

    return newImage;
}

- (CGRect) TransformCGRectForUIImageOrientation: (CGRect) source: (UIImageOrientation) orientation: (CGSize) imageSize {

    switch (orientation) {
        case UIImageOrientationLeft: { // EXIF #8
            CGAffineTransform txTranslate = CGAffineTransformMakeTranslation(
                                                                             imageSize.height, 0.0);
            CGAffineTransform txCompound = CGAffineTransformRotate(txTranslate,
                                                                   M_PI_2);
            return CGRectApplyAffineTransform(source, txCompound);
        }
        case UIImageOrientationDown: { // EXIF #3
            CGAffineTransform txTranslate = CGAffineTransformMakeTranslation(
                                                                             imageSize.width, imageSize.height);
            CGAffineTransform txCompound = CGAffineTransformRotate(txTranslate,
                                                                   M_PI);
            return CGRectApplyAffineTransform(source, txCompound);
        }
        case UIImageOrientationRight: { // EXIF #6
            CGAffineTransform txTranslate = CGAffineTransformMakeTranslation(
                                                                             0.0, imageSize.width);
            CGAffineTransform txCompound = CGAffineTransformRotate(txTranslate,
                                                                   M_PI + M_PI_2);
            return CGRectApplyAffineTransform(source, txCompound);
        }
        case UIImageOrientationUp: // EXIF #1 - do nothing
        default: // EXIF 2,4,5,7 - ignore
            return source;
    }

cropImage 方法似乎适用于从互联网下载的图像(不包含任何方向信息)。我的选项用完了。有人可以帮我吗？

感谢阅读!

Answer 1

如果可以的话，跳过使用 Core Graphics 绘制图像会更容易:

- (UIImage *)cropImage:(UIImage *)oldImage {
    CGSize imageSize = oldImage.size
    UIGraphicsBeginImageContextWithOptions( CGSizeMake( imageSize.width,
                                                        imageSize.height - 200),
                                            NO,
                                            0.);
    [oldImage drawAtPoint:CGPointMake( 0, -100)
                blendMode:kCGBlendModeCopy
                    alpha:1.];
    UIImage *croppedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return croppedImage;
}