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];
