ios - IOS: color only the transparent pixels

Question

If I have an image with some transparent pixels, is there any possibility to color the transparent pixels with white and make the rest of the image transparent in objective-c?

Thanks!

Answer 1

我找到了一个解决方案：

- (UIImage*)convertToInverseWhiteMask: (UIImage *) image {
    UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale);
    CGRect imageRect = CGRectMake(0.0f, 0.0f, image.size.width, image.size.height);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    // Draw a white background (for white mask)
    CGContextSetRGBFillColor(ctx, 1.0f, 1.0f, 1.0f, 1.0f);
    CGContextFillRect(ctx, imageRect);

    // Apply the source image's alpha
    [image drawInRect:imageRect blendMode:kCGBlendModeDestinationOut alpha:1.0f];

    UIImage* mask = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return mask; 
   }

Answer 2

这是我正在使用的：

- (UIImage *)imageWithTintedColor:(UIImage *)image withTint:(UIColor *)color withIntensity:(float)alpha
{
    CGSize size = image.size;

    UIGraphicsBeginImageContextWithOptions(size, FALSE, [[UIScreen mainScreen] scale]);
    CGContextRef context = UIGraphicsGetCurrentContext();

    [image drawAtPoint:CGPointZero blendMode:kCGBlendModeNormal alpha:1.0];

    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextSetBlendMode(context, kCGBlendModeSourceAtop);
    CGContextSetAlpha(context, alpha);

    CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(CGPointZero.x, CGPointZero.y, image.size.width, image.size.height));

    UIImage * tintedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return tintedImage;
}