使用透明背景反转图像的颜色 [英] Invert colors of image with transparent background

问题描述

我有一个带有透明背景的 uiimage.如果我使用follow方法反转颜色，透明背景会变为白色，然后变为黑色.

I have an uiimage with transparent background. if I invert the colors with the follow method, the transparent background change to white and then to black.

我希望它不反转透明像素?我怎样才能做到这一点?

I want that it doesnt invert transparent pixels? how can i do that?

-(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！

推荐答案

我就是这样解决的.

这是您可以在其他答案中找到的代码，但是使用相同图像和旋转上下文(用于从 CG* 坐标转换为 UI* 坐标)对当前图像进行遮罩.

It is the code that you can find in other answers, but with the masking of the current image with the same image, with rotated context (for transforming from CG* coords to 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;
}

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