根据顶部图像的 alpha/透明度混合两个 uiimage

Question

我正在尝试将背景与前景图像混合，其中前景图像是带有线条的透明图像。

我正在尝试这样做。

UIGraphicsBeginImageContext(CGSizeMake(320, 480));
CGContextRef context = UIGraphicsGetCurrentContext();   

// create rect that fills screen
CGRect bounds = CGRectMake( 0,0, 320, 480);

// This is my bkgnd image
CGContextDrawImage(context, bounds, [UIImage imageNamed:@"bkgnd.jpg"].CGImage);

CGContextSetBlendMode(context, kCGBlendModeSourceIn);

// This is my image to blend in
CGContextDrawImage(context, bounds, [UIImage imageNamed:@"over.png"].CGImage);

UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

UIImageWriteToSavedPhotosAlbum(outputImage, self, nil, nil);
// clean up drawing environment
//
UIGraphicsEndImageContext();

但似乎不起作用。

任何建议将不胜感激。

Answer 1

这是我在我的应用中所做的，类似于 Tyler 的 - 但没有 UIImageView：

UIImage *bottomImage = [UIImage imageNamed:@"bottom.png"];
UIImage *image = [UIImage imageNamed:@"top.png"];

CGSize newSize = CGSizeMake(width, height);
UIGraphicsBeginImageContext( newSize );

// Use existing opacity as is
[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
// Apply supplied opacity
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.8];

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

如果图像已经具有不透明度，则不需要设置它（如bottomImage），否则您可以设置它（如image）。

Answer 2

UIImage* bottomImage = [UIImage imageNamed:@"bottom.png"];  
UIImage* topImage    = [UIImage imageNamed:@"top.png"];
UIImageView* imageView = [[UIImageView alloc] initWithImage:bottomImage];
UIImageView* subView   = [[UIImageView alloc] initWithImage:topImage];
subView.alpha = 0.5;  // Customize the opacity of the top image.
[imageView addSubview:subView];
UIGraphicsBeginImageContext(imageView.frame.size);
[imageView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* blendedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[subView release];
[imageView release];

[self doWhateverIWantWith: blendedImage];

Answer 3

我的答案基于Eric's answer，但允许@2x 图像在图像合并后保留其分辨率。请注意我的 cmets 中的 URL REF，因为我承认对我在 iOS 应用程序中使用的此功能的开发提供帮助的来源。

- (UIImage*) mergeTwoImages : (UIImage*) topImage : (UIImage*) bottomImage
{
    // URL REF: http://iphoneincubator.com/blog/windows-views/image-processing-tricks
    // URL REF: https://stackoverflow.com/questions/1309757/blend-two-uiimages?answertab=active#tab-top
    // URL REF: http://www.waterworld.com.hk/en/blog/uigraphicsbeginimagecontext-and-retina-display

    int width = bottomImage.size.width;
    int height = bottomImage.size.height;

    CGSize newSize = CGSizeMake(width, height);
    static CGFloat scale = -1.0;

    if (scale<0.0)
    {
        UIScreen *screen = [UIScreen mainScreen];

        if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 4.0)
        {
            scale = [screen scale];
        }
        else
        {
            scale = 0.0;    // Use the standard API
        }
    }

    if (scale>0.0)
    {
        UIGraphicsBeginImageContextWithOptions(newSize, NO, scale);
    }
    else
    {
        UIGraphicsBeginImageContext(newSize);
    }

    [bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
    [topImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:1.0];

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

    return newImage;
}

Answer 4

与阿尔法混合

UIGraphicsBeginImageContext(area.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextRetain(context);

// mirroring context
CGContextTranslateCTM(context, 0.0, area.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

for (...) {
    CGContextBeginTransparencyLayer(context, nil);
    CGContextSetAlpha( context, alpha );
    CGContextDrawImage(context, area, tempimg.CGImage);
    CGContextEndTransparencyLayer(context);
}

// get created image
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
CGContextRelease(context);
UIGraphicsEndImageContext();

Answer 5

斯威夫特 3

此函数将获取两个图像和一个CGSize，并返回一个可选的UIImage。当两个图像大小相同时效果最佳。如果您的顶部图像具有 Alpha，它将通过它显示底部图像。

// composit two images
func compositeTwoImages(top: UIImage, bottom: UIImage, newSize: CGSize) -> UIImage? {
    // begin context with new size
    UIGraphicsBeginImageContextWithOptions(newSize, false, 0.0)
    // draw images to context
    bottom.draw(in: CGRect(origin: CGPoint.zero, size: newSize))
    top.draw(in: CGRect(origin: CGPoint.zero, size: newSize))
    // return the new image
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    // returns an optional
    return newImage
}

用法

let outputSize = CGSize(width: 100, height: 100)
if let topImage = UIImage(named: "myTopImage") {
    if let bottomImage = UIImage(named: "myBottomImage") {
        // composite both images
        if let finalImage = compositeTwoImages(top: topImage, bottom: bottomImage, newSize: outputSize) {
            // do something with finalImage
        }
    }
}

Answer 6

您能否详细说明“它似乎不起作用”的含义？它是只画一个图像还是另一个图像？画黑色？噪音？碰撞？为什么选择kCGBlendModeSourceIn；你想达到什么效果（有几十种混合图像的方法）？你的任何一张图片都已经有 Alpha 版了吗？

我假设你想要做的是混合两个图像，每个图像都有 50% 的不透明度？使用CGContextSetAlpha() 而不是CGContextSetBlendMode()。

Answer 7

您可以使用UIImage 的drawInRect: 或drawAtPoint: 代替CGContextDrawImage（它们绘制到当前上下文）。使用它们会给你的输出带来什么不同吗？

确保您从imageNamed: 返回的UIImage* 值有效也可能会有所帮助。