将 UIImage 分成两半？答案

【问题标题】：Split UIImage in half?将 UIImage 分成两半？
【发布时间】：2012-05-26 12:56:32
【问题描述】：

我将如何将 UIImage 分成两半（从中间向下）以便生成两个图像？

【问题讨论】：

【解决方案1】：

你可以试试这个，

UIImage *image = [UIImage imageNamed:@"yourImage.png"];
CGImageRef tmpImgRef = image.CGImage;
CGImageRef topImgRef = CGImageCreateWithImageInRect(tmpImgRef, CGRectMake(0, 0, image.size.width, image.size.height / 2.0));
UIImage *topImage = [UIImage imageWithCGImage:topImgRef];
CGImageRelease(topImgRef);

CGImageRef bottomImgRef = CGImageCreateWithImageInRect(tmpImgRef, CGRectMake(0, image.size.height / 2.0,  image.size.width, image.size.height / 2.0));
UIImage *bottomImage = [UIImage imageWithCGImage:bottomImgRef];
CGImageRelease(bottomImgRef);

希望对你有帮助，:)

【讨论】：

【解决方案2】：

- (void)splitImage:(UIImage *)image
{
    CGFloat imgWidth = image.size.width/2;
    CGFloat imgheight = image.size.height;

    CGRect leftImgFrame = CGRectMake(0, 0, imgWidth, imgheight);
    CGRect rightImgFrame = CGRectMake(imgWidth, 0, imgWidth, imgheight);

    CGImageRef left = CGImageCreateWithImageInRect(image.CGImage, leftImgFrame);
    CGImageRef right = CGImageCreateWithImageInRect(image.CGImage, rightImgFrame);

    // These are the images we want!
    UIImage *leftImage = [UIImage imageWithCGImage:left];
    UIImage *rightImage = [UIImage imageWithCGImage:right];

    // Don't forget to free the memory!
    CGImageRelease(left);
    CGImageRelease(right);
}

【讨论】：

这是唯一不会创建一大堆上下文的答案。 Quartz 在优化裁剪过程方面做得很好（直接获取图像的像素数据，而不是创建新的上下文，绘制图像，然后裁剪）。当我们将图像分成许多小部分时，这可能会快很多倍！

【解决方案3】：

iOS 11，swift 4.0 更新版本https://stackoverflow.com/users/893872/durul-dalkanat，老实说我认为是最好的:)

这会将图像分成 4 个部分

func splitImage(image2D: UIImage) -> [UIImage] {
    let imgWidth = image2D.size.width / 2
    let imgHeight = image2D.size.height / 2
    var imgImages:[UIImage] = []

    let leftHigh = CGRect(x: 0, y: 0, width: imgWidth, height: imgHeight)
    let rightHigh = CGRect(x: imgWidth, y: 0, width: imgHeight, height: imgHeight)
    let leftLow = CGRect(x: 0, y: imgHeight, width: imgWidth, height: imgHeight)
    let rightLow = CGRect(x: imgWidth, y: imgHeight, width: imgWidth, height: imgHeight)

    let leftQH = image2D.cgImage?.cropping(to:leftHigh)
    let rightHQ = image2D.cgImage?.cropping(to:rightHigh)
    let leftQL = image2D.cgImage?.cropping(to:leftLow)
    let rightQL = image2D.cgImage?.cropping(to:rightLow)

    imgImages.append(UIImage(cgImage: leftQH!))
    imgImages.append(UIImage(cgImage: rightHQ!))
    imgImages.append(UIImage(cgImage: leftQL!))
    imgImages.append(UIImage(cgImage: rightQL!))

    return imgImages
}

【讨论】：