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http://stackoverflow.com/questions/1434714/another-iphone-cgbitmapcontextcreateimage-leak
下面这个方法 可以改变图片大小 自适应,自己传参数吧
- (UIImage *)rescaleImageToSize:(CGSize)size {
CGRect rect = CGRectMake(0.0, 0.0, size.width, size.height);
UIGraphicsBeginImageContext(rect.size);
[self drawInRect:rect]; // scales image to rect
UIImage *resImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return resImage;
}
- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize; //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
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 
UIImage*)image scaledToSize 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 UIImage*)sourceImage scaledToSize 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 UIImage*)sourceImage scaledToSizeWithSameAspectRatio 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;
}
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原文地址：http://www.cnblogs.com/wj033/p/4498159.html
