如何將UIImage中的顏色「白色」更改爲透明

Question

我有一個生成爲截圖的UIImage。我加入這個對象用下面的代碼：

self.view.backgroundColor = [UIColor colorWithRed:1 green:1 blue:1 alpha:0.0]; 
    drawImage.backgroundColor = [UIColor colorWithRed:1 green:1 blue:1 alpha:0.0]; 

    UIGraphicsBeginImageContext(self.view.bounds.size); 
    [drawImage.layer renderInContext:UIGraphicsGetCurrentContext()]; 
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext(); 
    UIGraphicsEndImageContext(); 

    CGImageRef rawImageRef=viewImage.CGImage; 
    const float colorMasking[6] = {255,255,255,255,0,0}; 
    CGImageCreateWithMaskingColors(rawImageRef, colorMasking); 
    UIImage *newImage = [UIImage imageWithCGImage:rawImageRef]; 

但是我的圖片僅爲變白了，我想有圖像出現在哪裏這是通過使用CGImageCreateMaskingColors白色的地方是透明的。

希望有人能幫助我。

Answer 1

UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, YES, 1.0); 
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()]; 
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext(); 
UIGraphicsEndImageContext(); 

CGImageRef rawImageRef = viewImage.CGImage; 
const float colorMasking[6] = {255, 255, 255, 255, 255, 255}; 
UIGraphicsBeginImageContext(viewImage.size); 
CGImageRef maskedImageRef = CGImageCreateWithMaskingColors(rawImageRef, colorMasking); 
CGContextTranslateCTM(UIGraphicsGetCurrentContext(), 0.0, viewImage.size.height); 
CGContextScaleCTM(UIGraphicsGetCurrentContext(), 1.0, -1.0); 

CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, viewImage.size.width, viewImage.size.height), maskedImageRef); 
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext(); 
CGImageRelease(maskedImageRef); 
UIGraphicsEndImageContext();