iOS进行合成方式，本人知道的又两种：

1：使用UIImage直接合成

方法：通过上下文将要合成的图片都绘制到该上下文，然后得到合成的图片

- (UIImage*)NTESATCOverlayWith:(UIImage*)overlayImage{

UIGraphicsBeginImageContext(self.size);

[self drawAtPoint:CGPointZero];

[overlayImage drawInRect:CGRectMake(0, 0, self.size.width, self.size.height) blendMode:kCGBlendModeNormal alpha:0.9999999];

UIImage *combinedImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return combinedImage;

}

2：通过UIView进行

方法：将图片都加载到一个UIView上，然后通过UIView生成图片.

- (UIImage *) p_w_picpathFromView:(UIView *)view {

// we need to size the graphics context according to the device scale

CGFloat scale = [[UIScreen mainScreen] scale];

CGSize pageSize = view.frame.size;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef context = CGBitmapContextCreate(NULL,

pageSize.width*scale,

pageSize.height*scale,

8, /* bits per component*/

pageSize.width*scale * 4, /* bytes per row */

colorSpace,

kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrderDefault);

CGColorSpaceRelease(colorSpace);

CGContextClipToRect(context, CGRectMake(0, 0, pageSize.width*scale, pageSize.height*scale));

CGContextScaleCTM(context, scale, scale);

[view.layer renderInContext:context];

CGImageRef p_w_picpath = CGBitmapContextCreateImage(context);

CGContextRelease(context);

UIImage *destImaage = [UIImage p_w_picpathWithCGImage:p_w_picpath scale:1 orientation:UIImageOrientationDown | UIImageOrientationDownMirrored];

CGImageRelease(p_w_picpath);

return destImaage;

}