IOS读取图片（转载）

一.读取图片

1.从资源(resource)读取

[cpp] viewplaincopyprint?

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

2.从网络读取

[cpp] viewplaincopyprint?

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

3.从手机本地读取

[cpp] viewplaincopyprint?

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

4.从现有的context中获得图像

[cpp] viewplaincopyprint?

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

5.用Quartz的CGImageSourceRef来读取图片

[cpp] viewplaincopyprint?

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

二.保存图片

1.转换成NSData来保存图片（imgFromUrl是UIImage）

[cpp] viewplaincopyprint?

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

2.用Quartz的CGImageDestinationRef来输出图片，这个方式不常见，所以不做介绍，详细可以看apple文档Quartz2D Programming Guide

三.绘制图(draw|painting)

1.UIImageView方式加入到UIView层

[cpp] viewplaincopyprint?

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

2.[img drawAtPoint]系列方法

[cpp] viewplaincopyprint?

1. [image4 drawAtPoint:CGPointMake(100, 0)];    

3.CGContextDrawImage

[cpp] viewplaincopyprint?

1. 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

[cpp] viewplaincopyprint?

1. CGLayerRef cg=CGLayerCreateWithContext(ctx, CGSizeMake(320, 480), NULL);  
2. //需要将CGLayerContext来作为缓存context，这个是必须的  
3. CGContextRef layerContext=CGLayerGetContext(cg);  
4. CGContextDrawImage(layerContext, CGRectMake(160, 230, 160, 230), img);   
5. CGContextDrawLayerAtPoint(ctx, CGPointMake(0, 0), cg);  

5.CALayer的contents

[cpp] viewplaincopyprint?

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

四.其它

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=[UIImageimageWithCGImage:cgImage];