如何裁剪 UIImage？

Question

我开发了一个应用程序，在该应用程序中我使用其像素处理图像，但在该图像处理中需要大量时间。因此我想裁剪 UIImage（仅图像的中间部分，即删除/裁剪图像的边框部分）。我有开发代码，

- (NSInteger) processImage1: (UIImage*) image
{

 CGFloat width = image.size.width;
 CGFloat height = image.size.height;
 struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel));
 if (pixels != nil)
 {
  // Create a new bitmap
  CGContextRef context = CGBitmapContextCreate(
              (void*) pixels,
              image.size.width,
              image.size.height,
              8,
              image.size.width * 4,
              CGImageGetColorSpace(image.CGImage),
              kCGImageAlphaPremultipliedLast
              );
  if (context != NULL)
  {
   // Draw the image in the bitmap
   CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage);
   NSUInteger numberOfPixels = image.size.width * image.size.height;

   NSMutableArray *numberOfPixelsArray = [[[NSMutableArray alloc] initWithCapacity:numberOfPixelsArray] autorelease];
}

我如何拍摄（裁剪外边框）UIImage 的中间部分?????????

Answer 1

试试这样的：

CGImageRef imageRef = CGImageCreateWithImageInRect([largeImage CGImage], cropRect);
image = [UIImage imageWithCGImage:imageRef]; 
CGImageRelease(imageRef);

注意：cropRect 是图像中间部分的较小矩形...

Answer 2

我一直在寻找一种方法来获取 UIImage 的任意矩形裁剪（即子图像）。

如果图像的方向不是 UIImageOrientationUp，我尝试的大多数解决方案都不起作用。

例如：

http://www.hive05.com/2008/11/crop-an-image-using-the-iphone-sdk/

通常，如果您使用 iPhone 相机，您将有其他方向，如 UIImageOrientationLeft，并且您将无法通过上述方式获得正确的裁剪。这是因为使用了 CGImageRef/CGContextDrawImage，它们在 UIImage 的坐标系中有所不同。

下面的代码使用 UI* 方法（没有 CGImageRef），我已经用上/下/左/右方向的图像对此进行了测试，它似乎工作得很好。

// get sub image - (UIImage*) getSubImageFrom: (UIImage*) img WithRect: (CGRect) rect { UIGraphicsBeginImageContext(rect.size); CGContextRef context = UIGraphicsGetCurrentContext(); // translated rectangle for drawing sub image CGRect drawRect = CGRectMake(-rect.origin.x, -rect.origin.y, img.size.width, img.size.height); // clip to the bounds of the image context // not strictly necessary as it will get clipped anyway? CGContextClipToRect(context, CGRectMake(0, 0, rect.size.width, rect.size.height)); // draw image [img drawInRect:drawRect]; // grab image UIImage* subImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return subImage; }

Answer 3

因为我刚才需要它，这里是 Swift 4 中 M-V 的代码：

func imageWithImage(image: UIImage, croppedTo rect: CGRect) -> UIImage {

    UIGraphicsBeginImageContext(rect.size)
    let context = UIGraphicsGetCurrentContext()

    let drawRect = CGRect(x: -rect.origin.x, y: -rect.origin.y, 
                          width: image.size.width, height: image.size.height)

    context?.clip(to: CGRect(x: 0, y: 0, 
                             width: rect.size.width, height: rect.size.height))

    image.draw(in: drawRect)

    let subImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()
    return subImage!
}

Answer 4

如果您不仅可以设置 UIImageView 的图像，还可以设置要在该 UIImage 中显示的左上角偏移量，最终会更快，从精灵图集创建的图像要少得多。也许这是可能的。这肯定会省去很多努力！

同时，我在我的应用程序中使用的实用程序类中创建了这些有用的功能。它从另一个 UIImage 的一部分创建一个 UIImage，并使用标准 UIImageOrientation 值指定旋转、缩放和翻转选项。保留原始图像的像素缩放比例。

我的应用在初始化过程中创建了很多 UIImage，这必然需要时间。但是在选择某个选项卡之前不需要某些图像。为了让加载看起来更快，我可以在启动时产生的单独线程中创建它们，然后等到它在选择该选项卡时完成。

此代码也发布在Most efficient way to draw part of an image in iOS

+ (UIImage*)imageByCropping:(UIImage *)imageToCrop toRect:(CGRect)aperture {
    return [ChordCalcController imageByCropping:imageToCrop toRect:aperture withOrientation:UIImageOrientationUp];
}

// Draw a full image into a crop-sized area and offset to produce a cropped, rotated image
+ (UIImage*)imageByCropping:(UIImage *)imageToCrop toRect:(CGRect)aperture withOrientation:(UIImageOrientation)orientation {

            // convert y coordinate to origin bottom-left
    CGFloat orgY = aperture.origin.y + aperture.size.height - imageToCrop.size.height,
            orgX = -aperture.origin.x,
            scaleX = 1.0,
            scaleY = 1.0,
            rot = 0.0;
    CGSize size;

    switch (orientation) {
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
            size = CGSizeMake(aperture.size.height, aperture.size.width);
            break;
        case UIImageOrientationDown:
        case UIImageOrientationDownMirrored:
        case UIImageOrientationUp:
        case UIImageOrientationUpMirrored:
            size = aperture.size;
            break;
        default:
            assert(NO);
            return nil;
    }


    switch (orientation) {
        case UIImageOrientationRight:
            rot = 1.0 * M_PI / 2.0;
            orgY -= aperture.size.height;
            break;
        case UIImageOrientationRightMirrored:
            rot = 1.0 * M_PI / 2.0;
            scaleY = -1.0;
            break;
        case UIImageOrientationDown:
            scaleX = scaleY = -1.0;
            orgX -= aperture.size.width;
            orgY -= aperture.size.height;
            break;
        case UIImageOrientationDownMirrored:
            orgY -= aperture.size.height;
            scaleY = -1.0;
            break;
        case UIImageOrientationLeft:
            rot = 3.0 * M_PI / 2.0;
            orgX -= aperture.size.height;
            break;
        case UIImageOrientationLeftMirrored:
            rot = 3.0 * M_PI / 2.0;
            orgY -= aperture.size.height;
            orgX -= aperture.size.width;
            scaleY = -1.0;
            break;
        case UIImageOrientationUp:
            break;
        case UIImageOrientationUpMirrored:
            orgX -= aperture.size.width;
            scaleX = -1.0;
            break;
    }

    // set the draw rect to pan the image to the right spot
    CGRect drawRect = CGRectMake(orgX, orgY, imageToCrop.size.width, imageToCrop.size.height);

    // create a context for the new image
    UIGraphicsBeginImageContextWithOptions(size, NO, imageToCrop.scale);
    CGContextRef gc = UIGraphicsGetCurrentContext();

    // apply rotation and scaling
    CGContextRotateCTM(gc, rot);
    CGContextScaleCTM(gc, scaleX, scaleY);

    // draw the image to our clipped context using the offset rect
    CGContextDrawImage(gc, drawRect, imageToCrop.CGImage);

    // pull the image from our cropped context
    UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();

    // pop the context to get back to the default
    UIGraphicsEndImageContext();

    // Note: this is autoreleased
    return cropped;
}

Answer 5

使用函数

CGContextClipToRect(context, CGRectMake(0, 0, size.width, size.height));

这是一个示例代码，用于不同的目的，但可以剪辑。

- (UIImage *)aspectFillToSize:(CGSize)size
{
    CGFloat imgAspect = self.size.width / self.size.height;
    CGFloat sizeAspect = size.width/size.height;

    CGSize scaledSize;

        if (sizeAspect > imgAspect) { // increase width, crop height
            scaledSize = CGSizeMake(size.width, size.width / imgAspect);
        } else { // increase height, crop width
            scaledSize = CGSizeMake(size.height * imgAspect, size.height);
        }
    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0f);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextClipToRect(context, CGRectMake(0, 0, size.width, size.height));
    [self drawInRect:CGRectMake(0.0f, 0.0f, scaledSize.width, scaledSize.height)];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

Answer 6

#非常小/简单的 Swift 5 版本，

您不应该混合 UI 和 CG 对象，它们有时具有非常不同的坐标空间。这会让你难过。

注意?：self.draw(at:)

@inlinable private prefix func - (right: CGPoint) -> CGPoint
{
    return CGPoint(x: -right.x, y: -right.y)
}

extension UIImage
{
    public func cropped(to cropRect: CGRect) -> UIImage?
    {
           let renderer = UIGraphicsImageRenderer(size: cropRect.size)
        return renderer.image
        {
           _ in
           
            self.draw(at: -cropRect.origin)
        }
    }
}

Answer 7

如果您想在每张照片的中心裁剪肖像。

使用@M-V 解决方案，并替换cropRect。

CGFloat height = imageTaken.size.height;
CGFloat width = imageTaken.size.width;

CGFloat newWidth = height * 9 / 16;
CGFloat newX = abs((width - newWidth)) / 2;

CGRect cropRect = CGRectMake(newX,0, newWidth ,height);

Answer 8

我希望能够根据纵横比从区域裁剪，并根据外部边界范围缩放到大小。这是我的变体：

import AVFoundation
import ImageIO

class Image {

    class func crop(image:UIImage, source:CGRect, aspect:CGSize, outputExtent:CGSize) -> UIImage {

        let sourceRect = AVMakeRectWithAspectRatioInsideRect(aspect, source)
        let targetRect = AVMakeRectWithAspectRatioInsideRect(aspect, CGRect(origin: CGPointZero, size: outputExtent))

        let opaque = true, deviceScale:CGFloat = 0.0 // use scale of device's main screen
        UIGraphicsBeginImageContextWithOptions(targetRect.size, opaque, deviceScale)

        let scale = max(
            targetRect.size.width / sourceRect.size.width,
            targetRect.size.height / sourceRect.size.height)

        let drawRect = CGRect(origin: -sourceRect.origin * scale, size: image.size * scale)
        image.drawInRect(drawRect)

        let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return scaledImage
    }
}

有几件事让我感到困惑，裁剪和调整大小的不同问题。裁剪由您传递给 drawInRect 的矩形的原点处理，缩放由大小部分处理。就我而言，我需要将源上的裁剪矩形的大小与相同纵横比的输出矩形相关联。然后输出/输入比例因子，这需要应用于drawRect（传递给drawInRect）。

需要注意的是，这种方法有效地假设您正在绘制的图像大于图像上下文。我没有对此进行测试，但我认为您可以使用此代码来处理裁剪/缩放，但将比例参数明确定义为上述比例参数。默认情况下，UIKit 根据屏幕分辨率应用乘数。

最后，应该注意的是，这种 UIKit 方法比 CoreGraphics / Quartz 和 Core Image 方法级别更高，并且似乎可以处理图像方向问题。还值得一提的是，它的速度非常快，仅次于 ImageIO，根据这里的这篇文章：http://nshipster.com/image-resizing/