UIGraphicsBeginImageContext UIGraphicsGetImageFromCurrentImageContext 压缩，修改，截取图片_uigraphicsgetimagefromcurrentimagecontext() nil

//获取图片的缩略图
 
+ (UIImage *)thumbnailWithImageWithoutScale:(UIImage *)image size:(CGSize)asize{
 
    UIImage *newimage;
 
    if (nil == image) {
 
        newimage = nil;
 
    }
 
    else{
 
 
 
        CGSize oldsize = image.size;
 
        CGRect rect;
 
        if (asize.width/asize.height > oldsize.width/oldsize.height) {
 
            rect.size.width = asize.height*oldsize.width/oldsize.height;
 
            rect.size.height = asize.height;
 
            rect.origin.x = (asize.width - rect.size.width)/2;
 
            rect.origin.y = 0;
 
        }
 
        else{
 
            rect.size.width = asize.width;
 
            rect.size.height = asize.width*oldsize.height/oldsize.width;
 
            rect.origin.x = 0;
 
            rect.origin.y = (asize.height - rect.size.height)/2;
 
        }
 
        UIGraphicsBeginImageContext(asize);
 
        CGContextRef context = UIGraphicsGetCurrentContext();
 
        CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);
 
        UIRectFill(CGRectMake(0, 0, asize.width, asize.height));//clear background
 
        [image drawInRect:rect];
 
        newimage = UIGraphicsGetImageFromCurrentImageContext();
 
        UIGraphicsEndImageContext();
 
    }
 
    return newimage;
 
}
 
 
 
 
 
//获取等比例压缩的图像
+ (UIImage *)getPicZoomImage:(UIImage *)image {
    
    UIImage *img = image;
    
    int h = img.size.height;
    int w = img.size.width;
    if(h <= PicAfterZoomWidth && w <= PicAfterZoomHeight)
    {
        image = img;
    }
    else
    {
        float b = (float)PicAfterZoomWidth/w < (float)PicAfterZoomHeight/h ? (float)PicAfterZoomWidth/w : (float)PicAfterZoomHeight/h;
        CGSize itemSize = CGSizeMake(b*w, b*h);
        UIGraphicsBeginImageContext(itemSize);
        CGRect imageRect = CGRectMake(0, 0, b*w, b*h);
        [img drawInRect:imageRect];
        img = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
    return img;
}
 
 
/**
 * 修改图片大小
 */
+ (UIImage *) imageWithImageSimple:(UIImage*)image scaledToSize:(CGSize) newSize{
    newSize.height=image.size.height*(newSize.width/image.size.width);
    UIGraphicsBeginImageContext(newSize);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return  newImage;
}
 
//截取图片 根据frame
- (NSArray *)captureViews:(UIView *)theView frame:(NSArray *)fra{
    @autoreleasepool {
        NSMutableArray *imageViewArrReturn = [NSMutableArray array];
        UIGraphicsBeginImageContext(theView.frame.size);
        CGContextRef context = UIGraphicsGetCurrentContext();
        [theView.layer renderInContext:context];
        theView.layer.contents =nil;
        UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        for (int i = 0; i < fra.count; i++) {
            NSValue *frame = [fra objectAtIndex:i];
            
        
            CGImageRef ref = CGImageCreateWithImageInRect(img.CGImage, [frame CGRectValue]);
            UIImage *image = [UIImage imageWithCGImage:ref];
            [imageViewArrReturn addObject:image];
             CGImageRelease(ref);
        }
       
        CGContextRelease(context);
        return imageViewArrReturn;
    }
 
}