UIImage 加载和保存

一、图片读取

1、从资源(resource)读取

    UIImage* image = [UIImage imageNamed:@"1.jpg"]; 

2、从网络读取

    NSString *urlString = @"http://www.sinaimg.cn/qc/photo_auto/chezhan/2012/50/00/15/80046_950.jpg";
    NSURL *url = [NSURL URLWithString:urlString];  
    UIImage *imgFromUrl = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:url]];  

3、从手机本地读取

    // 读取本地图片非resource
    NSString *aPath3 = [NSString stringWithFormat:@"%@/Documents/%@.jpg",NSHomeDirectory(),@"test"];  
    UIImage *imgFromUrl3 = [[UIImage alloc]initWithContentsOfFile:aPath3];  
    UIImageView* imageView3 = [[UIImageView alloc] initWithImage:imgFromUrl3];  

4、从现有的context中获得图像

    // add ImageIO.framework and #import     
    CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)url, NULL);  
    CGImageRef img = CGImageSourceCreateImageAtIndex(source,0,NULL);  
    CGContextRef ctx = UIGraphicsGetCurrentContext();  
    CGContextSaveGState(ctx); 
    
    // transformCTM的2种方式  
    // CGContextConcatCTM(ctx, CGAffineTransformMakeScale(.2, -0.2));  
    // CGContextScaleCTM(ctx,1,-1);  
    
    // 注意坐标要反下,用ctx来作为图片源   
    CGImageRef capture = CGBitmapContextCreateImage(ctx);  
    CGContextDrawImage(ctx, CGRectMake(160, 0, 160, 230), [image CGImage]);  
    CGContextDrawImage(ctx, CGRectMake(160, 230, 160, 230), img);  
    CGImageRef capture2 = CGBitmapContextCreateImage(ctx); 

5、用Quartz的CGImageSourceRef来读取图片

    CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)url, NULL);  
    CGImageRef img = CGImageSourceCreateImageAtIndex(source,0,NULL); 

二、保存图片

1、转换成NSData来保存图片（imgFromUrl是UIImage）

    // 保存图片 2种获取路径都可以  
//    NSArray *paths=NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);  
//   NSString*documentsDirectory=[paths objectAtIndex:0];    
//   NSString*aPath=[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.jpg",@"test"]];   
    NSString *aPath=[NSString stringWithFormat:@"%@/Documents/%@.jpg",NSHomeDirectory(),@"test"];  
    NSData *imgData = UIImageJPEGRepresentation(imgFromUrl,0);      
    [imgData writeToFile:aPath atomically:YES];

2、用Quartz的CGImageDestinationRef来输出图片

三、绘制图(draw|painting)

1、UIImageView方式加入到UIView层

    UIImageView *imageView = [[UIImageView alloc] initWithImage:image];  
    imageView.frame = CGRectMake( 0, 0, 320, 480);  
    [self addSubview:imageView]; 

2、[img drawAtPoint]系列方法

    UIImage* image = [UIImage imageNamed:@"1.jpg"];
    [image drawAtPoint:CGPointMake(100, 0)]; 

3、CGContextDrawImage

    UIImage* image = [UIImage imageNamed:@"1.jpg"];
    CGContextDrawImage(ctx, CGRectMake(160, 0, 160, 230), [image CGImage]);

4.CGLayer

    // 这个是apple推荐的一种offscreen的绘制方法，相比bitmapContext更好，因为它似乎会利用iphone硬件(drawing-card)加速
    CGLayerRef cg=CGLayerCreateWithContext(ctx, CGSizeMake(320, 480), NULL);  
    // 需要将CGLayerContext来作为缓存context，这个是必须的  
    CGContextRef layerContext=CGLayerGetContext(cg);  
    CGContextDrawImage(layerContext, CGRectMake(160, 230, 160, 230), img);   
    CGContextDrawLayerAtPoint(ctx, CGPointMake(0, 0), cg); 

5、CALayer的contents

    UIImage* image=[UIImage imageNamed:@"1.jpg"];  
    CALayer *ly=[CALayer layer];  
    ly.frame=CGRectMake(0, 0, 320, 460);  
    ly.contents=[image CGImage];  
    [self.layer addSublayer:ly]; 

其他

1、CGImage和UIImage互换

    // 这样就可以随时切换UIKit和Quartz之间类型，并且选择您熟悉的方式来处理图片.
    CGImage cgImage=[uiImage CGImage];
    UIImage* uiImage=[UIImage imageWithCGImage:cgImage];