UIImage 图片处理：截图，缩放，设定大小，存储

图片的处理大概分 截图(capture),  缩放(scale), 设定大小(resize),  存储(save)

1.等比率缩放

- (UIImage *)scaleImage:(UIImage *)image toScale:(float)scaleSize

{

UIGraphicsBeginImageContext(CGSizeMake(image.size.width * scaleSize, image.size.height * scaleSize);
[image drawInRect:CGRectMake(0, 0, image.size.width * scaleSize, image.size.height * scaleSize)];
UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return scaledImage;

}

2.自定长宽

- (UIImage *)reSizeImage:(UIImage *)image toSize:(CGSize)reSize

{
UIGraphicsBeginImageContext(CGSizeMake(reSize.width, reSize.height));
[image drawInRect:CGRectMake(0, 0, reSize.width, reSize.height)];
UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return reSizeImage;

}

3.处理某个特定View
只要是继承UIView的object 都可以处理
必须先import QuzrtzCore.framework

-(UIImage*)captureView:(UIView *)theView

{
CGRect rect = theView.frame;
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[theView.layer renderInContext:context];
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return img;

}

4.储存图片
储存图片这里分成储存到app的文件里和储存到手机的图片库里

1) 储存到app的文件里

NSString *path = [[NSHomeDirectory()stringByAppendingPathComponent:@"Documents"]stringByAppendingPathComponent:@"image.png"];
[UIImagePNGRepresentation(image) writeToFile:pathatomically:YES];

把要处理的图片, 以image.png名称存到app home下的Documents目录里

2)储存到手机的图片库里(必须在真机使用，模拟器无法使用)

CGImageRef screen = UIGetScreenImage();
UIImage* image = [UIImage imageWithCGImage:screen];
CGImageRelease(screen);
UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);
UIGetScreenImage(); // 原来是private(私有)api, 用来截取整个画面,不过SDK 4.0后apple就开放了

//====================================================================================

以下代码用到了Quartz Framework 和 Core Graphics Framework. 在workspace的framework目录里添加这两个framework.在UIKit里，图像类UIImage和CGImageRef的画图操作都是通过Graphics Context来完成。Graphics Context封装了变换的参数，使得在不同的坐标系里操作图像非常方便。缺点就是，获取图像的数据不是那么方便。下面会给出获取数据区的代码。

1. 从UIView中获取图像相当于窗口截屏。

(iOS提供全局的全屏截屏函数UIGetScreenView(). 如果需要特定区域的图像，可以crop一下)

CGImageRef screen = UIGetScreenImage();
UIImage* image = [UIImage imageWithCGImage:screen];

2. 对于特定UIView的截屏。

（可以把当前View的layer，输出到一个ImageContext中，然后利用这个ImageContext得到UIImage）

-(UIImage*)captureView: (UIView *)theView

{

CGRect rect = theView.frame;

UIGraphicsBeginImageContext(rect.size);

CGContextRef context =UIGraphicsGetCurrentContext();

[theView.layer renderInContext:context];

UIImage *img = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return img;
}

3. 如果需要裁剪指定区域。

（可以path & clip，以下例子是建一个200x200的图像上下文，再截取出左上角）

UIGraphicsBeginImageContext(CGMakeSize(200,200));

CGContextRefcontext=UIGraphicsGetCurrentContext();

UIGraphicsPushContext(context);

// ...把图写到context中，省略[indent]CGContextBeginPath();

CGContextAddRect(CGMakeRect(0,0,100,100));

CGContextClosePath();[/indent]CGContextDrawPath();

CGContextFlush(); // 强制执行上面定义的操作

UIImage* image = UIGraphicGetImageFromCurrentImageContext();

UIGraphicsPopContext();

4. 存储图像。

（分别存储到home目录文件和图片库文件。）

存储到目录文件是这样

NSString *path = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"image.png"];
[UIImagePNGRepresentation(image) writeToFile:path atomically:YES];

若要存储到图片库里面

UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);

5.  互相转换UImage和CGImage。

（UImage封装了CGImage, 互相转换很容易）

UIImage* imUI=nil;
CGImageRef imCG=nil;

imUI = [UIImage initWithCGImage:imCG];

imCG = imUI.CGImage;

6. 从CGImage上获取图像数据区。

（在apple dev上有QA, 不过好像还不支持ios）

下面给出一个在ios上反色的例子

-(id)invertContrast:(UIImage*)img
{

CGImageRef inImage = img.CGImage; 

CGContextRef ctx;

CFDataRef m_DataRef;

m_DataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage)); 

int width = CGImageGetWidth( inImage );

int height = CGImageGetHeight( inImage );

int bpc = CGImageGetBitsPerComponent(inImage);

int bpp = CGImageGetBitsPerPixel(inImage);

int bpl = CGImageGetBytesPerRow(inImage);

UInt8 * m_PixelBuf = (UInt8 *) CFDataGetBytePtr(m_DataRef);

int length = CFDataGetLength(m_DataRef);

NSLog(@"len %d", length);

NSLog(@"width=%d, height=%d", width, height);

NSLog(@"1=%d, 2=%d, 3=%d", bpc, bpp,bpl);

for (int index = 0; index < length; index += 4)

{ 

m_PixelBuf[index + 0] = 255 - m_PixelBuf[index + 0];// b

m_PixelBuf[index + 1] = 255 - m_PixelBuf[index + 1];// g

m_PixelBuf[index + 2] = 255 - m_PixelBuf[index + 2];// r

}

ctx = CGBitmapContextCreate(m_PixelBuf, width, height, bpb, bpl, CGImageGetColorSpace( inImage ), kCGImageAlphaPremultipliedFirst );

CGImageRef imageRef = CGBitmapContextCreateImage (ctx);

UIImage* rawImage = [UIImage imageWithCGImage:imageRef];

CGContextRelease(ctx);

return rawImage;

}

7. 显示图像数据区。

（显示图像数据区，也就是unsigned char*转为graphics context或者UIImage或和CGImageRef）

CGContextRef ctx = CGBitmapContextCreate(pixelBuf,width,height, bitsPerComponent,bypesPerLine, colorSpace,kCGImageAlphaPremultipliedLast );
CGImageRef imageRef = CGBitmapContextCreateImage (ctx);

UIImage* image = [UIImage imageWithCGImage:imageRef];

NSString* path = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"ss.png"];

[UIImagePNGRepresentation(self.image) writeToFile:path atomically:YES];

CGContextRelease(ctx);

得到图像数据区后就可以很方便的实现图像处理的算法。