UIImage 图片处理：截图，缩放，设定大小，存储

图片的处理大概就分 截图(capture), 缩放(scale),设定大小(resize), 存储(save)
这几样比较好处理, 另外还有滤镜,擦试等, 以后再说
在这个Demo code裡, 我写了几个方法

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, 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];
這樣就把你要處理的圖片, 以image.png這個檔名存到app home底下的Documents目錄裡

2)储存到手机的图片库里
CGImageRef screen = UIGetScreenImage();
UIImage* image = [UIImage imageWithCGImage:screen];
CGImageRelease(screen);
UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);
UIGetScreenImage()原本是private(私有)api, 用來截取整個畫麵
不過SDK 4.0後apple就開放了

另外儲存到手機的圖片庫裡, 必須在實機使用, 模擬器無法使用

以
下代碼用到了Quartz Framework和Core Graphics Framework.
在workspace的framework目錄裏添加這兩個framework.在UIKit裏，圖像類UIImage和CGImageRef的畫圖操作
都是通過Graphics Context來完成。Graphics
Context封裝了變換的參數，使得在不同的坐標係裏操作圖像非常方便。缺點就是，獲取圖像的數據不是那麼方便。下麵會給出獲取數據區的代碼。

從UIView中獲取圖像相當於窗口截屏。ios提供全局的全屏截屏函數UIGetScreenView(). 如果需要特定區域的圖像，可以crop一下。

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

對於特定UIView的截屏，可以把當前View的layer，輸出到一個ImageContext中，然後利用這個ImageContext得到UIImage

1. -(UIImage*)captureView: (UIView *)theView
2. {
3. CGRect rect = theView.frame;
4. UIGraphicsBeginImageContext(rect.size);
5. CGContextRef context =UIGraphicsGetCurrentContext();
6. [theView.layer renderInContext:context];
7. UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
8. UIGraphicsEndImageContext();
9. return img;
10. }

如果需要裁剪製定區域，可以path & clip，以下例子是建一個200x200的圖像上下文，再截取出左上角

1. UIGraphicsBeginImageContext(CGMakeSize(200,200));
2. CGContextRefcontext=UIGraphicsGetCurrentContext();
3. UIGraphicsPushContext(context);
4. // ...把图写到context中，省略[indent]CGContextBeginPath();
5. CGContextAddRect(CGMakeRect(0,0,100,100));
6. CGContextClosePath();[/indent]CGContextDrawPath();
7. CGContextFlush(); // 强制执行上面定义的操作
8. UIImage* image = UIGraphicGetImageFromCurrentImageContext();
9. UIGraphicsPopContext();

存储图像分为存储到home目录文件和图片库文件。存储到目录文件是这样

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

若要存储到图片库里面

1. UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);

UImage封装了CGImage, 互相转换很容易

1. UIImage* imUI=nil;
2. CGImageRef imCG=nil;
3. imUI = [UIImage initWithCGImage:imCG];
4. imCG = imUI.CGImage;

從CGImage上獲取圖像數據區，在apple dev上有QA, 不過好像還不支持ios
下麵給出一個在ios上反色的例子

1. -(id)invertContrast:(UIImage*)img
2. {
3. CGImageRef inImage = img.CGImage;
4. CGContextRef ctx;
5. CFDataRef m_DataRef;
6. m_DataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));
7. int width = CGImageGetWidth( inImage );
8. int height = CGImageGetHeight( inImage );
9. int bpc = CGImageGetBitsPerComponent(inImage);
10. int bpp = CGImageGetBitsPerPixel(inImage);
11. int bpl = CGImageGetBytesPerRow(inImage);
12. UInt8 * m_PixelBuf = (UInt8 *) CFDataGetBytePtr(m_DataRef);
13. int length = CFDataGetLength(m_DataRef);
14. NSLog(@"len %d", length);
15. NSLog(@"width=%d, height=%d", width, height);
16. NSLog(@"1=%d, 2=%d, 3=%d", bpc, bpp,bpl);
17. for (int index = 0; index < length; index += 4)
18. {
19. m_PixelBuf[index + 0] = 255 - m_PixelBuf[index + 0];// b
20. m_PixelBuf[index + 1] = 255 - m_PixelBuf[index + 1];// g
21. m_PixelBuf[index + 2] = 255 - m_PixelBuf[index + 2];// r
22. }
23. ctx
    = CGBitmapContextCreate(m_PixelBuf, width, height, bpb, bpl,
    CGImageGetColorSpace( inImage ), kCGImageAlphaPremultipliedFirst );
24. CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
25. UIImage* rawImage = [UIImage imageWithCGImage:imageRef];
26. CGContextRelease(ctx);
27. return rawImage;
28. }

得到圖像數據區後就可以很方便的實現圖像處理的算法。下麵給顯示圖像數據區的方法，也就是unsigned char*轉為graphics context或者UIImage或和CGImageRef

1. CGContextRef
   ctx = CGBitmapContextCreate(pixelBuf,width,height,
   bitsPerComponent,bypesPerLine, colorSpace,kCGImageAlphaPremultipliedLast
   );
2. CGImageRef imageRef = CGBitmapContextCreateImage (ctx);
3. UIImage* image = [UIImage imageWithCGImage:imageRef];
4. NSString* path = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"ss.png"];
5. [UIImagePNGRepresentation(self.image) writeToFile:path atomically:YES];
6. CGContextRelease(ctx);