如何从 UIImagePickerController 镜像 UIImage 图片

Question

我想弄清楚是否有任何方法可以镜像图像。例如，拍摄某人脸部的照片，然后将其切成两半，并显示他们的脸部在每一面都镜像后的样子。 CGAffineTransform 函数中似乎没有类似的技巧。请各位图形专家帮忙！！！

Answer 1

这里的基本“技巧”是使用关于 X 或 Y 轴的缩放变换，系数为 -1。例如，您可以使用它来创建“绕水平轴翻转”变换：

CGAffineTransform transform = CGAffineTransformScale(transform, -1, 1);

然后您可以在 UIImageView 上设置 transform 属性来翻转指定的图像，或者将其与另一个变换连接起来以实现更复杂的效果。为了获得您所描述的确切效果，您可能需要编写一些自定义绘图代码以将原始图像绘制到上下文中，然后将翻转的一半覆盖在其顶部。这在 Core Graphics 中相对简单。

Answer 2

如果您只打算支持 4.0+

UIImageOrientation flippedOrientation = UIImageOrientationUpMirrored;
switch (image.imageOrientation) {
  case UIImageOrientationUp: break;
  case UIImageOrientationDown: flippedOrientation = UIImageOrientationDownMirrored; break;
  // ...
}
UIImage * flippedImage = [UIImage imageWithCGImage:image.CGImage scale:image.scale orientation:flippedOrientation];

Answer 3

您可能会想，为什么要费心冗长的 switch 语句呢？

? UIImage *flip = [UIImage imageWithCGImage:image.CGImage   
?                                     scale:image.scale
?                               orientation:(image.imageOrientation + 4) % 8];

如果你看一下枚举，你会发现模运算就可以了：

typedef NS_ENUM(NSInteger, UIImageOrientation) {
    UIImageOrientationUp,            // default orientation
    UIImageOrientationDown,          // 180 deg rotation
    UIImageOrientationLeft,          // 90 deg CCW
    UIImageOrientationRight,         // 90 deg CW
    UIImageOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip
    UIImageOrientationDownMirrored,  // horizontal flip
    UIImageOrientationLeftMirrored,  // vertical flip
    UIImageOrientationRightMirrored, // vertical flip
};

但是这段代码太聪明了。您应该编写一个带有显式 switch 语句的函数。例如

UIImageOrientation mirroredImageOrientation(UIImageOrientation orientation) {
    switch(orientation) {
        case UIImageOrientationUp: return UIImageOrientationUpMirrored;
        case UIImageOrientationDown: return UIImageOrientationDownMirrored;
        case UIImageOrientationLeft: return UIImageOrientationLeftMirrored;
        case UIImageOrientationRight: return UIImageOrientationRightMirrored;
        case UIImageOrientationUpMirrored: return UIImageOrientationUp;
        case UIImageOrientationDownMirrored: return UIImageOrientationDown;
        case UIImageOrientationLeftMirrored: return UIImageOrientationLeft;
        case UIImageOrientationRightMirrored: return UIImageOrientationRight;
        default: return orientation;
    }
}

，使用这样的函数：

UIImage *flip = [UIImage imageWithCGImage:image.CGImage   
                                    scale:image.scale
                              orientation:mirroredImageOrientation(image.imageOrientation)];

我添加了问号来指示有问题的、有臭味的代码。类似于 编程实践

Answer 4

上面的答案都没有回答问题中镜像一半图像而不是翻转整个图像的部分。混合解决方案会产生以下示例函数，您可以将其用作类别，例如 UIImage+Mirroring ：

(UIImage *) horizontalMirror {
    UIImageOrientation flippedOrientation = UIImageOrientationUpMirrored;
    switch (self.imageOrientation) {
        case UIImageOrientationUp: break;
        case UIImageOrientationDown: flippedOrientation = UIImageOrientationDownMirrored; break;
    }
    UIImage * flippedImage = [UIImage imageWithCGImage:self.CGImage scale:1.0 orientation:flippedOrientation];

    CGImageRef inImage = self.CGImage;
    CGContextRef ctx = CGBitmapContextCreate(NULL,
                                             CGImageGetWidth(inImage),
                                             CGImageGetHeight(inImage),
                                             CGImageGetBitsPerComponent(inImage),
                                             CGImageGetBytesPerRow(inImage),
                                             CGImageGetColorSpace(inImage),
                                             CGImageGetBitmapInfo(inImage)
                                             );
    CGRect cropRect = CGRectMake(flippedImage.size.width/2, 0, flippedImage.size.width/2, flippedImage.size.height);
    CGImageRef TheOtherHalf = CGImageCreateWithImageInRect(flippedImage.CGImage, cropRect);
    CGContextDrawImage(ctx, CGRectMake(0, 0, CGImageGetWidth(inImage), CGImageGetHeight(inImage)), inImage);

    CGAffineTransform transform = CGAffineTransformMakeTranslation(flippedImage.size.width, 0.0);
    transform = CGAffineTransformScale(transform, -1.0, 1.0);
    CGContextConcatCTM(ctx, transform);

    CGContextDrawImage(ctx, cropRect, TheOtherHalf);

    CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
    CGContextRelease(ctx);
    UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);

    return finalImage;
}

Answer 5

使用更简单：

UIImage(assetIdentifier: .myIcon)?.withHorizontallyFlippedOrientation()

Answer 6

您可以在 Swift 4.0 中使用以下代码

 func didTakePicture(_ real_image: UIImage) {
   //suppose real_image = :)
 var flipped_image = UIImage(CGImage: real_image.CGImage!, scale: real_image.scale, orientation: .leftMirrored)
  // flipped_image is  (:
  }