[ios] iOS图片相关(读取、保存、绘制、其它相关) 【转】

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一.读取图片

1.从资源(resource)读取

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

2.从网络读取

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NSURL *url=[NSURL URLWithString:@"http://www.sinaimg.cn/qc/photo_auto/chezhan/2012/50/00/15/80046_950.jpg"];

UIImage *imgFromUrl =[[UIImage alloc]initWithData:[NSData dataWithContentsOfURL:url]];

3.从手机本地读取

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//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

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//add ImageIO.framework and #import <ImageIO/ImageIO.h>

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

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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）

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//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，这个方式不常见，所以不做介绍，详细可以看apple文档Quartz 2D Programming Guide

三.绘制图(draw|painting)

1.UIImageView方式加入到UIView层

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UIImageView* imageView=[[UIImageView alloc]initWithImage:image];

imageView.frame=CGRectMake(0, 0, 320, 480);

[self addSubview:imageView];

[imageView release];

2.[img drawAtPoint]系列方法

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

3.CGContextDrawImage

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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

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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

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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];

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.

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CGImage cgImage=[uiImage CGImage];

UIImage* uiImage=[UIImage imageWithCGImage:cgImage];

2.UIImage resizableImageWithCapInsets的问题

假设一张44x29的图片，同样的Insets=UIEdgeInsetsMake(10,10,10,10)在@2x情况和非@2x情况下，表现会有不
同，非@2x是OK正常的，但是如果同样尺寸的图片变成@2x,则导致在切换过渡的时候会很卡，应该是在不同的重绘导致的，表面原因是因为Insets设
置的是点，在@2x情况下拉伸，其实拉升的像素是上面20，下面也是20，但是图片其实只有29，所以导致不正确，只要将insets设置
成=UIEdgeInsetsMake(5,10,5,10)就正常了，所以以后要注意了。

3.动画图片使用注意

animationImage 设置完毕以后要startAnimation.不会自动启动动画图片。

此外在读取大量动画图片的时候不太适合用这个方法，因为一下子那么多图片容易爆掉。可以用这个方法替代，具体我也没试，方法就是手动切换图片，并非直接使用系统方法而已。

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imgV=[[UIImageView alloc]initWithFrame:CGRectMake(40, 40, 128, 128)];

[self.window addSubview:imgV];

[self performSelectorInBackground:@selector(playAnim)withObject:nil];

[imgV release];

-(void)playAnim{

for (int i=0;i<101;){

usleep(100000);

UIImage *image=[[UIImage alloc]initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:@"%d",i+1 ] ofType:@"tiff"]];

[self performSelectorOnMainThread:@selector(changeImage:) withObject:image waitUntilDone:YES];

i++;

}

}

-(void)changeImage:(UIImage*)image{

imgV.image=image;

}

相关帖子：http://www.cocoachina.com/bbs/read.php?tid=110154

4.UIControl设置UIImage

问题描述主要是有一个很小的叉按钮，需要响应很大的点击区域，这个其实很简单，代码如下：

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UIImage *bg=[UIImage imageNamed:@"heizi1.jpg"];

//图片大于点及区域，缩小下就行

bg=[self scaleImage:bg ToSize:(CGSize){100,100}];

UIButton* button = [[UIButton alloc]initWithFrame:CGRectMake(0, 0, 200, 200)];

//图片大于button，则会被拉伸，如果小于button则居中显示

[button setImage:bg forState:UIControlStateNormal];

此外多说一句，这个icon图片如果要准备2套图,缩放毕竟消耗效率

缩放图片代码

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-(UIImage *)scaleImage:(UIImage *)img ToSize:(CGSize)itemSize{

UIImage *i;

// CGSize itemSize=CGSizeMake(30, 30);

UIGraphicsBeginImageContext(itemSize);

CGRect imageRect=CGRectMake(0, 0, itemSize.width, itemSize.height);

[img drawInRect:imageRect];

i=UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return i;

从view截图出来

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#import <QuartzCore/QuartzCore.h>

-(UIImage *)getImageFromView:(UIView *)orgView{

UIGraphicsBeginImageContext(orgView.bounds.size);

[orgView.layer renderInContext:UIGraphicsGetCurrentContext()];

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return image;

}

CompressionQuality就是压缩质量的意思，数值越大，JPG文件越清楚。一般电脑上设计的JPG文件是72的。