Question

对于给定的UIImage，我的目标是生成另一个UIImage，它是原始图像的对角镜像版本。我正在使用Core Graphics来实现这一点。

我的尝试是为对角镜像操作生成仿射变换矩阵，如下所示：

| 0 1 0 |
| 1 0 0 |
| 0 0 1 |

但是得到的图像是旋转的图像，而不是对角镜像......

更具体地说，这是我尝试过的代码：

+ (UIImage *)mirrorImageDiagonal:(UIImage *)fromImage 
{
    CGContextRef mainViewContentContext = MyCreateBitmapContext(fromImage.size.width, fromImage.size.height);


    CGAffineTransform transform = CGAffineTransformIdentity;
    transform.a = 0;
    transform.b = 1;
    transform.c = 1;
    transform.d = 0;
    transform.tx = 0;
    transform.ty = 0;
    CGContextConcatCTM(mainViewContentContext, transform);

    // draw the image into the bitmap context
    CGContextDrawImage(mainViewContentContext, CGRectMake(0, 0, fromImage.size.width, fromImage.size.height), fromImage.CGImage);

    // create CGImageRef of the main view bitmap content, and then release that bitmap context
    CGImageRef reflectionImage = CGBitmapContextCreateImage(mainViewContentContext);
    CGContextRelease(mainViewContentContext);

    // convert the finished reflection image to a UIImage
    UIImage *theImage = [UIImage imageWithCGImage:reflectionImage];

    // image is retained by the property setting above, so we can release the original
    CGImageRelease(reflectionImage);

    return theImage;
}

转换矩阵存在问题吗？或者我如何使用核心图形？

Answer 1

您正在使用的矩阵将应用关于坐标对角线的变换，而不是关于图像的对角线。（除非图像具有方形尺寸，在这种情况下它们是相同的轴）。

你得到的图像然而它似乎是一个旋转，但实际上它是一个倒像;

+ (UIImage *)mirrorImageDiagonal1:(UIImage *)fromImage{

        //large square (max(h,w),max(h,w))
        CGSize neededSize = CGSizeMake(fromImage.size.height, fromImage.size.height);//should be max(h,w)

        UIGraphicsBeginImageContext(mirrorSize);
        CGContextRef context = UIGraphicsGetCurrentContext();

        // Tanslate and scale upside-down to compensate for Quartz's inverted coordinate system

        CGContextTranslateCTM(context, 0, fromImage.size.height);
        CGContextScaleCTM(context, 1.0, -1.0);


        CGAffineTransform transform = CGAffineTransformIdentity;
        transform.a = 0;
        transform.b = 1;
        transform.c = 1;
        transform.d = 0;
        transform.tx = 0;
        transform.ty = 0;
        //transform = CGAffineTransformInvert(transform);
        CGContextConcatCTM(context, transform);

        // draw the image into the bitmap context
        CGContextDrawImage(context, CGRectMake(0,0 , fromImage.size.width, fromImage.size.height), fromImage.CGImage);



        // create CGImageRef of the main view bitmap content, and then release that bitmap context

        CGImageRef reflectionImage = CGBitmapContextCreateImage(context);

        CGContextRelease(context);

        // convert the finished reflection image to a UIImage
        UIImage *theImage = [UIImage imageWithCGImage:reflectionImage];

        // image is retained by the property setting above, so we can release the original
        CGImageRelease(reflectionImage);

        return theImage;
    }

iOS：如何使用Core Graphics对图像进行对角镜像

1 个答案: