UIimage的缩放线程实现安全和非线程安全操作

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 thedesired

// 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*)imageWithImageUIImage*)sourceImagescaledToSizeWithSameAspectRatioCGSize)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 andscaledHeight,

// 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;