根据顶部图像的alpha /透明度混合两个uiimages

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.

我试图这样做.

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();

但似乎没有用.

任何建议将不胜感激.

Answer 1

这就是我在我的应用程序中所做的,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,则无需进行设置(如bottomImage),否则可以进行设置(如同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的答案,但允许@ 2x图像在图像合并后保留其分辨率.请注意我的评论中的URL REF,因为我承认为我在iOS应用程序中使用的此功能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

您可以使用UIImage'sdrawInRect: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任何差异吗？

确保UIImage*您返回的值imageNamed:有效也可能会有所帮助。