iOS：裁剪从 UIImagePickerController 相机抓取的静止图像，并带有叠加层

Question

我是 iOS 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 StackOverflow 上的更多随机问题。从这些，我发现>=iOS 4.0，所有从相机拍摄的图像都包含基于EXIF的旋转信息。

什么不工作：尝试不同的图像裁剪技术后，我最终只是在一些随机角落裁剪图像，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），裁剪正在工作。通过随机角，我的意思是 - 图像最终在右上角/左上角被裁剪并放大.

我想要完成的工作：
我正在尝试从顶部裁剪图像100 px，从底部裁剪100 px。本质上，我使用两个覆盖条 - 1 个在顶部，1 个在底部，CGRect(0.0, 0.0, SCREEN_WIDTH, 100.0) [顶部有一个 100.0 px 高条] 和另一个 CGRect(0.0, SCREEN_HEIGHT - 100, SCREEN_WIDTH, 100.0) [另一个 100 px 底部的高条]。我需要在这两个条带之间获取图像：我假设图像的高度是：SCREEN_HEIGHT - 200.0。

显示带有叠加层的相机的 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 属性旋转图像并对其进行裁剪的代码

- (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 Internet 下载的图像（不包含任何方向信息）。 我的选择已经不多了。有人可以帮我吗？

感谢阅读！

Answer 1

如果可以，使用 Core Graphics 更容易跳过绘制图像：

- (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;
}