用透明背景反转图像的颜色

Question

我有一个透明背景的uiimage。如果我用以下方法反转颜色，透明背景变为白色然后变为黑色。

我想它不会反转透明像素？我怎样才能做到这一点？

-(UIImage *) getImageWithInvertedPixelsOfImage:(UIImage *)image {
UIGraphicsBeginImageContextWithOptions(image.size, NO, 2);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);
[image drawInRect:CGRectMake(0, 0, image.size.width, image.size.height)];
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeDifference);
CGContextSetFillColorWithColor(UIGraphicsGetCurrentContext(),[UIColor whiteColor].CGColor);
CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, image.size.width, image.size.height));
UIImage * result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return result;

}

谢谢！

Answer 1

这就是我解决的问题。

这是您可以在其他答案中找到的代码，但是使用相同图像屏蔽当前图像，使用旋转上下文（用于从CG * coords转换为UI * coords）。

- (UIImage *)invertImage:(UIImage *)originalImage
{
    UIGraphicsBeginImageContext(originalImage.size);
    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);
    CGRect imageRect = CGRectMake(0, 0, originalImage.size.width, originalImage.size.height);
    [originalImage drawInRect:imageRect];


    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeDifference);
    // translate/flip the graphics context (for transforming from CG* coords to UI* coords
    CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0, originalImage.size.height);
    CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0);
    //mask the image
    CGContextClipToMask(UIGraphicsGetCurrentContext(), imageRect,  originalImage.CGImage);
    CGContextSetFillColorWithColor(UIGraphicsGetCurrentContext(),[UIColor whiteColor].CGColor);
    CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, originalImage.size.width, originalImage.size.height));
    UIImage *returnImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return returnImage;
}

Answer 2

我从@ maggix的答案中创建了一个Pod：

pod 'UIImage+InvertedImage'

Answer 3

这是@maggix答案的Swift 4.0版本......

func invertImage(with originalImage: UIImage) -> UIImage? {
    var image: UIImage?
    UIGraphicsBeginImageContext(originalImage.size)
    if let context = UIGraphicsGetCurrentContext() {
        context.setBlendMode(.copy)
        let imageRect = CGRect(x: 0, y: 0, width: originalImage.size.width, height: originalImage.size.height)
        originalImage.draw(in: imageRect)
        context.setBlendMode(.difference)
        // translate/flip the graphics context (for transforming from CG* coords to UI* coords
        context.translateBy(x: 0, y: originalImage.size.height)
        context.scaleBy(x: 1.0, y: -1.0)
        //mask the image
        context.clip(to: imageRect, mask: originalImage.cgImage!)
        context.setFillColor(UIColor.white.cgColor)
        context.fill(CGRect(x: 0, y:0, width: originalImage.size.width, height: originalImage.size.height))

        image = UIGraphicsGetImageFromCurrentImageContext()
    }
    UIGraphicsEndImageContext()
    return image
}