如何将透明PNG图像与颜色合并

Question

我尝试过drawInRect,CGContextDrawImage但它适用于整个图像.

我希望它仅适用于图像部分,而不是透明部分.有谁知道怎么做？

Answer 1

您可以使用UIImagealpha通道作为绘图的蒙版.

Objective-C的

- (UIImage *)overlayImage:(UIImage *)image withColor:(UIColor *)color
{
    //  Create rect to fit the PNG image
    CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);

    //  Start drawing
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSaveGState(context);

    //  Fill the rect by the final color
    [color setFill];
    CGContextFillRect(context, rect);

    //  Make the final shape by masking the drawn color with the images alpha values
    CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
    [image drawInRect:rect blendMode:kCGBlendModeDestinationIn alpha:1];

    //  Create new image from the context
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();

    //  Release context
    UIGraphicsEndImageContext();

    return img;
}

用法示例:

UIImage *pngImage = [UIImage imageNamed:@"myImage"];
UIColor *overlayColor = [UIColor magentaColor];

UIImage *image = [self overlayImage:pngImage withColor:overlayColor];

斯威夫特3

extension UIImage {

    func overlayed(by overlayColor: UIColor) -> UIImage {
        //  Create rect to fit the image
        let rect = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)

        // Create image context. 0 means scale of device's main screen
        UIGraphicsBeginImageContextWithOptions(rect.size, false, 0)
        let context = UIGraphicsGetCurrentContext()!

        //  Fill the rect by the final color
        overlayColor.setFill()
        context.fill(rect)

        //  Make the final shape by masking the drawn color with the images alpha values
        self.draw(in: rect, blendMode: .destinationIn, alpha: 1)

        //  Create new image from the context
        let overlayedImage = UIGraphicsGetImageFromCurrentImageContext()!

        //  Release context
        UIGraphicsEndImageContext()

        return overlayedImage
    }
}

用法示例:

let overlayedImage = myImage.overlayed(by: .magenta)

编辑:正如Desdenova在评论中指出的那样,我误解了这个问题.我原来的答案是在彩色背景上绘制PNG.答案已编辑,下面的代码是原始代码.

- (UIImage *)combineImage:(UIImage *)image withBackgroundColor:(UIColor *)bgColor
{
    //  Create rect to fit the PNG image
    CGRect rect = CGRectMake(0, 0, image.size.width, image.size.height);

    //  Create bitmap contect
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSaveGState(context);

    // Draw background first

    //  Set background color (will be under the PNG)
    [bgColor setFill];

    //  Fill all context with background image
    CGContextFillRect(context, rect);

    //  Draw the PNG over the background
    [image drawInRect:rect];

    //  Create new image from the context
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();

    //  Release context
    UIGraphicsEndImageContext();

    return img;
}

Answer 2

感谢您的帮助...我尝试了这段代码，它终于对我有用了。

UIGraphicsBeginImageContext(firstImage.size);

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, firstImage.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGRect rect = CGRectMake(0, 0, firstImage.size.width, firstImage.size.height);
// draw black background to preserve color of transparent pixels
CGContextSetBlendMode(context, kCGBlendModeNormal);
[[UIColor whiteColor] setFill];
CGContextFillRect(context, rect);
// draw original image
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextDrawImage(context, rect, firstImage.CGImage);
// tint image (loosing alpha) - the luminosity of the original image is preserved
CGContextSetBlendMode(context, kCGBlendModeDarken);
[[UIColor colorWithPatternImage:secondImage] setFill];
CGContextFillRect(context, rect);
// mask by alpha values of original image
CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
CGContextDrawImage(context, rect, firstImage.CGImage);
//[firstImage drawInRect:rect];

// image drawing code here
UIImage *coloredImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();