任何新的位图绘制代码是鼓励使用UIGraphicsImageRenderer leiu这个API

UIKIT_EXTERN void    UIGraphicsBeginImageContext(CGSize size);

UIKIT_EXTERN void    UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale) NS_AVAILABLE_IOS(4_0);

UIKIT_EXTERN UIImage* __nullable UIGraphicsGetImageFromCurrentImageContext(void);

UIKIT_EXTERN void    UIGraphicsEndImageContext(void);

1.等比缩放

- (UIImage *) scaleImage:(UIImage *)image dengbiScale:(float)dengbiScale {

UIGraphicsBeginImageContext(CGSizeMake(image.size.width * dengbiScale, image.size.height * dengbiScale);

[image drawInRect:CGRectMake(0, 0, image.size.width * dengbiScale, image.size.height * dengbiScale)];

UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return scaledImage;

}

2.自定义大小

- (UIImage *) reSizeImage:(UIImage *)image scaletoSize:(CGSize)scaletoSize {

UIGraphicsBeginImageContext(CGSizeMake(scaletoSize.width, scaletoSize.height));

[image drawInRect:CGRectMake(0, 0, scaletoSize.width, scaletoSize.height)];

UIImage *mySizeImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return mySizeImage;

}

3.处理某个特定的View

-(UIImage*) captureView:(UIView *)tedingView {

CGRect rect = tedingView.frame;

UIGraphicsBeginImageContext(rect.size);

CGContextRef context = UIGraphicsGetCurrentContext();

[tedingView.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;

}