IOS UIGraphicsBeginImageContext

1.等比缩放

• (UIImage *) scaleImage:(UIImage *)image toScale:(float)scaleSize {
  UIGraphicsBeginImageContext(CGSizeMake(image.size.width * scaleSize, image.size.height * scaleSize);
  [image drawInRect:CGRectMake(0, 0, image.size.width * scaleSize, image.size.height * scaleSize)];
  UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return scaledImage;
  }

2.自定义大小

• (UIImage *) reSizeImage:(UIImage *)image toSize:(CGSize)reSize {
  UIGraphicsBeginImageContext(CGSizeMake(reSize.width, reSize.height));
  [image drawInRect:CGRectMake(0, 0, reSize.width, reSize.height)];
  UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return reSizeImage;
  }

3.处理某个特定的View

-(UIImage*) captureView:(UIView *)theView {
CGRect rect = theView.frame;
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[theView.layer renderInContext:context];
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return img;
}

4.储存图片（存入到文件夹中）
NSString *path = [[NSHomeDirectory()stringByAppendingPathComponent:@"Documents"]stringByAppendingPathComponent:@"image.png"];
[UIImagePNGRepresentation(image) writeToFile:pathatomically:YES];

5.储存到手机的图片库中

CGImageRef screen = UIGetScreenImage();
UIImage* image = [UIImage imageWithCGImage:screen];
CGImageRelease(screen);
UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);

6.根据给定得图片，从其指定区域截取一张新得图片
-(UIImage )getImageFromImage{
//大图bigImage
//定义myImageRect，截图的区域
CGRect myImageRect = CGRectMake(10.0, 10.0, 57.0, 57.0);
UIImage bigImage= [UIImage imageNamed:@"k00030.jpg"];
CGImageRef imageRef = bigImage.CGImage;
CGImageRef subImageRef = CGImageCreateWithImageInRect(imageRef, myImageRect);
CGSize size;
size.width = 57.0;
size.height = 57.0;
UIGraphicsBeginImageContext(size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, myImageRect, subImageRef);
UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
UIGraphicsEndImageContext();
return smallImage;
}

7. 合并两张图片

• (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2 {
  UIGraphicsBeginImageContext(image1.size);
  // Draw image1
  [image1 drawInRect:CGRectMake(0, 0, image1.size.width, image1.size.height)];
  // Draw image2
  [image2 drawInRect:CGRectMake(0, 0, image2.size.width, image2.size.height)];
  UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return resultingImage;
  }