在iOS中如何将两张图混合成一张图呢？比如有一张是透明图，另外一张是不透明的，混合为一张图，并且保存起来。有关保存可见。

上图所示，可将红色手绘的色彩图片和原来的图层混合。

 

代码如下：

-(void)generateImageToPhotoAlbum{ 

    NSLog(@"save image to photo album."); 

    

    UIGraphicsBeginImageContext(CGSizeMake(1024, 768)); 

    [drawImage.image drawInRect:self.frame]; 

    

    UIImage *foregroundImage=[UIImage imageWithCGImage:(CGImageRef)foregroundLayer.contents]; 

    [foregroundImage drawInRect:self.frame blendMode:kCGBlendModeNormal alpha:1.0]; 

    

    UIImage *newImage=UIGraphicsGetImageFromCurrentImageContext(); 

    UIGraphicsEndImageContext(); 

    

    UIImageWriteToSavedPhotosAlbum(newImage, nil, nil, nil); 

}

本文参考了：

错误代码：

I'm trying to blend a background with a foreground image, where the foreground image is a transparent image with lines on it.

I am trying to do it this way.

1 UIGraphicsBeginImageContext(CGSizeMake(320,480));  2 CGContextRef context =UIGraphicsGetCurrentContext();    4 // create rect that fills screen  5 CGRect bounds =CGRectMake(0,0,320,480);  7 // This is my bkgnd image  8 CGContextDrawImage(context, bounds,[UIImage imageNamed:@"bkgnd.jpg"].CGImage);  9 CGContextSetBlendMode(context, kCGBlendModeSourceIn); //CGContextSetAlpha(); 11 // This is my image to blend in 12 CGContextDrawImage(context, bounds,[UIImage imageNamed:@"over.png"].CGImage); 14 UIImage*outputImage =UIGraphicsGetImageFromCurrentImageContext(); 16 UIImageWriteToSavedPhotosAlbum(outputImage,self,nil,nil); 17 // clean up drawing environment 18 UIGraphicsEndImageContext();

but does not seem to work.

Any suggestions will be appreciated.

 

方法1：上层图片设置绘画属性    【 drawInRect:  blendMode:  alpha: 】    

This is what I've done in my app, similar to Tyler's - but without the UIImageView:

1 UIImage*bottomImage =[UIImage imageNamed:@"bottom.png"];  2 UIImage*image =[UIImage imageNamed:@"top.png"];  4 CGSize newSize =CGSizeMake(width, height);  5 UIGraphicsBeginImageContext( newSize );  7 // Use existing opacity as is  8 [bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];  9 // Apply supplied opacity 10 [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.8]; 12 UIImage*newImage =UIGraphicsGetImageFromCurrentImageContext(); 14 UIGraphicsEndImageContext();

方法2：两张图片放在同一个UIImageView中,然后用

[imageView.layer renderInContext:UIGraphicsGetCurrentContext()]  渲染。

1 UIImage* bottomImage = [UIImage imageNamed:@"bottom.png"];   2 UIImage* topImage    = [UIImageNamed:@"top.png"];  3 UIImageView* imageView = [[UIImageView alloc] initWithImage:bottomImage];  4 UIImageView* subView   = [[UIImageView alloc] initWithImage:topImage];  5 subView.alpha = 0.5;  // Customize the opacity of the top image.  6 [imageView addSubview:subView];  7 UIGraphicsBeginImageContext(imageView.frame.size);  8 [imageView.layer renderInContext:UIGraphicsGetCurrentContext()];  9 UIImage* blendedImage = UIGraphicsGetImageFromCurrentImageContext(); 10 UIGraphicsEndImageContext(); 11 [subView release]; 12 [imageView release]; 13 14 [self doWhateverIWantWith: blendedImage];

If there are alpha values within the top image's png file, just leave out the "subView.alpha = 0.5;" line, and it will draw the top image, including it's custom alpha values, on top of the bottom image. 

Blending with alpha

1 UIGraphicsBeginImageContext(area.size);  2 CGContextRef context = UIGraphicsGetCurrentContext();  3 CGContextRetain(context);  4  5 // mirroring context  6 CGContextTranslateCTM(context, 0.0, area.size.height);  7 CGContextScaleCTM(context, 1.0, -1.0);  8  9 for (...) {
    10     CGContextBeginTransparencyLayer(context, nil); 11     CGContextSetAlpha( context, alpha ); 12     CGContextDrawImage(context, area, tempimg.CGImage); 13     CGContextEndTransparencyLayer(context); 14 } 15 16 // get created image 17 UIImage *image = UIGraphicsGetImageFromCurrentImageContext(); 18 CGContextRelease(context); 19 UIGraphicsEndImageContext();

Suggestion: You can use UIImage's drawInRect: or drawAtPoint: instead of CGContextDrawImage (they draw to the current context). Does using them give you any difference in output?

It may also be helpful to make sure the UIImage* values you are getting back from imageNamed:are valid.