iOS图片生成小缩略图保证图片不模糊

-(UIImage *)imageCompressForSize:(UIImage *)sourceImage targetSize:(CGSize)size{

UIImage *newImage = nil;

CGSize imageSize = sourceImage.size;

CGFloat width = imageSize.width;

CGFloat height = imageSize.height;

CGFloat targetWidth = size.width;

CGFloat targetHeight = size.height;

CGFloat scaleFactor = 0.0;

CGFloat scaledWidth = targetWidth;

CGFloat scaledHeight = targetHeight;

CGPoint thumbnailPoint = CGPointMake(0.0, 0.0);

if(CGSizeEqualToSize(imageSize, size) == NO){

CGFloat widthFactor = targetWidth / width;

CGFloat heightFactor = targetHeight / height;

if(widthFactor > heightFactor){

scaleFactor = widthFactor;

}

else{

scaleFactor = heightFactor;

}

scaledWidth = width * scaleFactor;

scaledHeight = height * scaleFactor;

if(widthFactor > heightFactor){

thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;

}else if(widthFactor < heightFactor){

thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;

}

}

UIGraphicsBeginImageContextWithOptions(size, NO, 3.0);

CGRect thumbnailRect = CGRectZero;

thumbnailRect.origin = thumbnailPoint;

thumbnailRect.size.width = scaledWidth;

thumbnailRect.size.height = scaledHeight;

[sourceImage drawInRect:thumbnailRect];

newImage = UIGraphicsGetImageFromCurrentImageContext();

if(newImage == nil){

NSLog(@"scale image fail");

}

UIGraphicsEndImageContext();

return newImage;

}