在 iOS 8.4 中裁剪 UIImage 并发症 [重复]

Question

我目前正在用我的 - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info 方法如下：

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{   
    picker.allowsEditing = YES;

    UIImage *img = [info objectForKey:UIImagePickerControllerOriginalImage];

    CGRect cropRect = CGRectMake(0, 0, 2448, 3264);

    UIImage *croppedImage = [img crop:cropRect];

    imageToPass = croppedImage;

    NSLog(@"Here's imageToPass: %@", imageToPass);
    NSLog(@"and here's imageToPass' width: %f", imageToPass.size.width);
    NSLog(@"and here's imageToPass' height: %f", imageToPass.size.height);
    NSLog(@"and here's imageToPass' scale: %f", imageToPass.scale);

    UINavigationController *postControl = [self.storyboard instantiateViewControllerWithIdentifier:@"postControl"];
    RGPostViewController *postView = (RGPostViewController *)postControl.topViewController;

    [postView storeImage:imageToPass];

    [self.presentedViewController presentViewController:postControl animated:NO completion:nil];
}

我的问题是，当我打印 imageToPass 变量的宽度和高度时，我发现该值以点为单位列出。我的控制台打印如下：

我需要返回一个裁剪为 320x320 大小的图像。使用我的代码CGRect cropRect = CGRectMake(0, 0, 2448, 3264); 我采用照片的原始尺寸，默认情况下 UIImagePickerController 是，我假设，320x520 或类似的东西。使用点值我可以看到 2448 是点宽，3264 是点高度。来自谷歌，

iPhone 5 的显示分辨率为 1136 x 640 像素。新触摸屏的对角线尺寸为 4 英寸，纵横比为 16:9，并带有 326 ppi（每英寸像素）的 Retina 显示屏。

我不知道在这里做什么。 2448points/640px = 3.825 的数学是否告诉我在 326ppi 屏幕上每个像素有 3.825 个点？

PS 请记住，我正在尝试在 UIImagePickerControllerOriginalImage 中间抓取 320x320 图片，这意味着切割一些顶部像素数和一些底部像素数，以我假设的点数确定。

编辑

这是上面第四行代码中crop:方法的代码：

#import "UIImage+Crop.h"

@implementation UIImage (Crop)

- (UIImage *)crop:(CGRect)rect {

    rect = CGRectMake(rect.origin.x*self.scale,
                      rect.origin.y*self.scale,
                      rect.size.width*self.scale,
                      rect.size.height*self.scale);

    CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);
    UIImage *result = [UIImage imageWithCGImage:imageRef
                                          scale:self.scale
                                    orientation:self.imageOrientation];
    CGImageRelease(imageRef);
    return result;
}

@end

我发现如果我将CGRect cropRect 设置为CGRect cropRect = CGRectMake(264, 0, 2448, 3000); //3264，它实际上会从图像的顶部和底部移除264 个点。我了解 iPhone 5s 的屏幕分辨率为 326ppi（每英寸像素），我该如何使用它来成功移除需要移除的像素数量。

Answer 1

由于屏幕的属性scale，您无需了解转换点/像素/视网膜/非/等。不过，您确实需要使用核心图形来进行实际裁剪。下面是它的样子：

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {   
    picker.allowsEditing = YES;

    UIImage *img = [info objectForKey:UIImagePickerControllerOriginalImage];

    // you want to make your rect in the center of your image, not at [0,0]
    CGFloat cropSize = 320;
    CGRect cropRect = CGRectMake(img.center.x - (cropSize / 2), img.center.y - (cropSize / 2), cropSize, cropSize);

    // Make a new CGImageRef with the current graphics context, then use that to make the cropped UIImage. Make sure to release that image ref!
    CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], cropRect);
    croppedImage = [UIImage imageWithCGImage: imageRef];
    CGImageRelease(imageRef);

    // Adjust the image for scale - this is how you handle retina/orientation.
    imageToPass = [UIImage imageWithCGImage:imageRef 
                                      scale:self.scale 
                                orientation:self.imageOrientation];

    UINavigationController *postControl = [self.storyboard instantiateViewControllerWithIdentifier:@"postControl"];
    RGPostViewController *postView = (RGPostViewController *)postControl.topViewController;

    [postView storeImage:imageToPass];

    [self.presentedViewController presentViewController:postControl animated:NO completion:nil];
}