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UIGraphicsBeginImageContext系列知识 收藏人：求知665 2015-05-14 | 阅：  转：    |   来源   |  分享

- (UIImage *)rescaleImage:(UIImage *)img ToSize:(CGSize)size; //图片缩放裁剪 - (UIImage*)transformWidth:(CGFloat)width height:(CGFloat)height; //改变大小 + (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2; //合并图片 + (UIImage *)imageFromImage:(UIImage *)image inRect:(CGRect)rect; //裁剪部分图片 + (void)imageSavedToPhotosAlbum:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo; //保存图片到媒体库 零）重新设置图片的尺寸 - (UIImage *)rescaleImage:(UIImage *)img ToSize:(CGSize)size { CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height); UIGraphicsBeginImageContext(rect.size); [img drawInRect:rect]; // scales image to rect UIImage *resImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return resImage; } －）根据给定得图片，从其指定区域截取一张新得图片 -(UIImage *)getImageFromImage{ //大图bigImage //定义myImageRect，截图的区域 CGRect myImageRect = CGRectMake(10.0, 10.0, 57.0, 57.0); UIImage* bigImage= [UIImage imageNamed:@"k00030.jpg"]; CGImageRef imageRef = bigImage.CGImage; CGImageRef subImageRef = CGImageCreateWithImageInRect(imageRef, myImageRect); CGSize size; size.width = 57.0; size.height = 57.0; UIGraphicsBeginImageContext(size); CGContextRef context = UIGraphicsGetCurrentContext(); CGContextDrawImage(context, myImageRect, subImageRef); UIImage* smallImage = [UIImage imageWithCGImage:subImageRef]; UIGraphicsEndImageContext(); return smallImage; } 二） 合并两张图片 - (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2 { UIGraphicsBeginImageContext(image1.size); // Draw image1 [image1 drawInRect:CGRectMake(0, 0, image1.size.width, image1.size.height)]; // Draw image2 [image2 drawInRect:CGRectMake(0, 0, image2.size.width, image2.size.height)]; UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return resultingImage; } 三） 捕捉屏幕截图 CALayer实例使用Core Graphics的renderInContext方法可以将视图绘制到图像上下文中以便转化为其他UIImage实例。前提先#import + (UIImage *) imageFromView: (UIView *)theView {     // draw a view's contents into an image context   UIGraphicsBeginImageContext(theView.frame.size);    CGContextRef  context = UIGraphicsGetCurrentContext();    [theView.layer  renderInContext:context];    UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();    UIGraphicsEndImageContext();     return theImage; } 注：UIGraphicsBeginImageContext(CGSize size)创建一个基于位图的上下文(context)，并将其设置为当前上下文。函数功能与UIGraphicsBeginImageContextWithOptions相同，相当于该方法的opaque参数为NO，scale因子为1.0。而UIGraphicsEndImageContext()方法是移除栈顶的基于当前位图的图形上下文。 视图添加倒影效果 const CGFloat kReflectPercent = -0.25f; const CGFloat kReflectOpacity = 0.3f; const CGFloat kReflectDistance = 10.0f; + (void)addSimpleReflectionToView:(UIView *)theView {      CALayer *reflectionLayer = [CALayer layer];      reflectionLayer.contents = [theView layer].contents;      reflectionLayer.opacity = kReflectOpacity;      reflectionLayer.frame = CGRectMake(0.0f,0.0f,theView.frame.size.width,theView.frame.size.height*kReflectPercent);  //倒影层框架设置，其中高度是原视图的百分比    CATransform3D stransform = CATransform3DMakeScale(1.0f,-1.0f,1.0f);      CATransform3D transform = CATransform3DTranslate(stransform,0.0f,-(kReflectDistance + theView.frame.size.height),0.0f);      reflectionLayer.transform = transform;      reflectionLayer.sublayerTransform = reflectionLayer.transform;      [[theView layer] addSublayer:reflectionLayer]; } 另一：使用Core Graphics创建倒影 + (CGImageRef) createGradientImage:(CGSize)size {       CGFloat colors[] = {0.0,1.0,1.0,1.0};       //在灰色设备色彩上建立一渐变     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();       CGContextRef context = CGBitmapContextCreate(nil,size.width,size.height,8,0,colorSpace,kCGImageAlphaNone);       CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace,colors,NULL,2);       CGColorSpaceRelease(colorSpace);       //绘制线性渐变     CGPoint p1 = CGPointZero;       CGPoint p2 = CGPointMake(0,size.height);       CGContextDrawLinearGradient(context,gradient,p1,p2,kCGGradientDrawsAfterEndLocation);       //Return the CGImage      CGImageRef theCGImage = CGBitmapContextCreateImage(context);       CFRelease(gradient);       CGContextRelease(context);       return theCGImage; } //Create a shrunken frame for the reflection + (UIImage *) reflectionOfView:(UIView *)theView WithPercent:(CGFloat) percent {      //Retain the width but shrink the height     CGSize size = CGSizeMake(theView.frame.size.width, theView.frame.size.height * percent);      //Shrink the View     UIGraphicsBeginImageContext(size);      CGContextRef context = UIGraphicsGetCurrentContext();      [theView.layer renderInContext:context];      UIImage *partialimg = UIGraphicsGetImageFromCurrentImageContext();      UIGraphicsEndImageContext();      //build the mask     CGImageRef mask = [ImageHelper createGradientImage:size];      CGImageRef ref = CGImageCreateWithMask(partialimg.CGImage,mask);      UIImage *theImage = [UIImage imageWithCGImage:ref];      CGImageRelease(ref);      CGImageRelease(mask);      return theImage; } const CGFloat kReflectDistance = 10.0f; + (void) addReflectionToView: (UIView *)theView {      theView.clipsToBounds = NO;      UIImageView *reflection = [[UIImageView alloc] initWithImage:[ImageHelper reflectionOfView:theView withPercent:0.45f]];      CGRect frame = reflection.frame;      frame.origin = CGPointMake(0.0f, theView.frame.size.height + kReflectDistance);      reflection.frame = frame;      // add the reflection as a simple subview     [theView addSubView:reflection];      [reflection release]; } 关于图片缩放的线程安全和非线程安全操作. 非线程安全的操作只能在主线程中进行操作,对于大图片的处理肯定会消耗大量的时间,如下面的方法 方法 1： 使用 UIKit + (UIImage*)imageWithImage INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET UIImage*)image scaledToSize INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET CGSize)newSize; { // Create a graphics image context UIGraphicsBeginImageContext(newSize); // Tell the old image to draw in this new context, with the desired // new size [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)]; // Get the new image from the context UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext(); // End the context UIGraphicsEndImageContext(); // Return the new image. return newImage; } 此方法很简单， 但是，这种方法不是线程安全的情况下. 方法 2： 使用 CoreGraphics + (UIImage*)imageWithImage INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET UIImage*)sourceImage scaledToSize INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET CGSize)newSize; { CGFloat targetWidth = targetSize.width; CGFloat targetHeight = targetSize.height; CGImageRef imageRef = [sourceImage CGImage]; CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef); CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef); if (bitmapInfo == kCGImageAlphaNone) { bitmapInfo = kCGImageAlphaNoneSkipLast; } CGContextRef bitmap; if (sourceImage.imageOrientation == UIImageOrientationUp ||sourceImage.imageOrientation == UIImageOrientationDown) { bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo); } else { bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo); } if (sourceImage.imageOrientation == UIImageOrientationLeft) { CGContextRotateCTM (bitmap, radians(90)); CGContextTranslateCTM (bitmap, 0, -targetHeight); } else if (sourceImage.imageOrientation ==UIImageOrientationRight) { CGContextRotateCTM (bitmap, radians(-90)); CGContextTranslateCTM (bitmap, -targetWidth, 0); } else if (sourceImage.imageOrientation == UIImageOrientationUp) { // NOTHING } else if (sourceImage.imageOrientation == UIImageOrientationDown){ CGContextTranslateCTM (bitmap, targetWidth, targetHeight); CGContextRotateCTM (bitmap, radians(-180.)); } CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth,targetHeight), imageRef); CGImageRef ref = CGBitmapContextCreateImage(bitmap); UIImage* newImage = [UIImage imageWithCGImage:ref]; CGContextRelease(bitmap); CGImageRelease(ref); return newImage; } 这种方法的好处是它是线程安全，加上它负责的 （使用正确的颜色空间和位图信息，处理图像方向） 的小东西，UIKit 版本不会。 如何调整和保持长宽比 （如 AspectFill 选项）？ 它是非常类似于上述，方法，它看起来像这样： + (UIImage*)imageWithImage INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET UIImage*)sourceImage scaledToSizeWithSameAspectRatio INCLUDEPICTURE "http://www.61ic.com/Mobile/UploadFiles_9667/201103/20110309123315372.gif" \* MERGEFORMATINET CGSize)targetSize; { CGSize imageSize = sourceImage.size; CGFloat width = imageSize.width; CGFloat height = imageSize.height; CGFloat targetWidth = targetSize.width; CGFloat targetHeight = targetSize.height; CGFloat scaleFactor = 0.0; CGFloat scaledWidth = targetWidth; CGFloat scaledHeight = targetHeight; CGPoint thumbnailPoint = CGPointMake(0.0,0.0); if (CGSizeEqualToSize(imageSize, targetSize) == NO) { CGFloat widthFactor = targetWidth / width; CGFloat heightFactor = targetHeight / height; if (widthFactor > heightFactor) { scaleFactor = widthFactor; // scale to fit height } else { scaleFactor = heightFactor; // scale to fit width } scaledWidth = width * scaleFactor; scaledHeight = height * scaleFactor; // center the image if (widthFactor > heightFactor) { thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; } else if (widthFactor < heightFactor) { thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5; } } CGImageRef imageRef = [sourceImage CGImage]; CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef); CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef); if (bitmapInfo == kCGImageAlphaNone) { bitmapInfo = kCGImageAlphaNoneSkipLast; } CGContextRef bitmap; if (sourceImage.imageOrientation == UIImageOrientationUp ||sourceImage.imageOrientation == UIImageOrientationDown) { bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo); } else { bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth,CGImageGetBitsPerComponent(imageRef),CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo); } // In the right or left cases, we need to switch scaledWidth and scaledHeight, // and also the thumbnail point if (sourceImage.imageOrientation == UIImageOrientationLeft) { thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x); CGFloat oldScaledWidth = scaledWidth; scaledWidth = scaledHeight; scaledHeight = oldScaledWidth; CGContextRotateCTM (bitmap, radians(90)); CGContextTranslateCTM (bitmap, 0, -targetHeight); } else if (sourceImage.imageOrientation ==UIImageOrientationRight) { thumbnailPoint = CGPointMake(thumbnailPoint.y, thumbnailPoint.x); CGFloat oldScaledWidth = scaledWidth; scaledWidth = scaledHeight; scaledHeight = oldScaledWidth; CGContextRotateCTM (bitmap, radians(-90)); CGContextTranslateCTM (bitmap, -targetWidth, 0); } else if (sourceImage.imageOrientation == UIImageOrientationUp) { // NOTHING } else if (sourceImage.imageOrientation == UIImageOrientationDown){ CGContextTranslateCTM (bitmap, targetWidth, targetHeight); CGContextRotateCTM (bitmap, radians(-180.)); } CGContextDrawImage(bitmap, CGRectMake(thumbnailPoint.x,thumbnailPoint.y, scaledWidth, scaledHeight), imageRef); CGImageRef ref = CGBitmapContextCreateImage(bitmap); UIImage* newImage = [UIImage imageWithCGImage:ref]; CGContextRelease(bitmap); CGImageRelease(ref); return newImage; }