调整UIImage尺寸适应UIImageView

Question

有一个 3264 × 2448图片， imageView尺寸768 × 1024，我需要调整图片尺寸适应视图，但是不能让图片质量下降。

试过下面的方法：

- (UIImage *)imageByScalingProportionallyToSize: (CGSize)targetSize {

   UIImage *sourceImage = self;
   UIImage *newImage = nil;
   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;
        else
            scaleFactor = heightFactor;
        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;
       }
    }
    // this is actually the interesting part:
    UIGraphicsBeginImageContext(targetSize);
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    [sourceImage drawInRect:thumbnailRect];
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    if(newImage == nil) NSLog(@"could not scale image");
    return newImage ;
}

Answer 1

试试

+ (UIImage*)imageWithImage:(UIImage*)image 
               scaledToSize:(CGSize)newSize;
{
   UIGraphicsBeginImageContext( newSize );
   [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
   UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

   return newImage;
}

指定新尺寸(768,1024) 然后传递初始图片，但是要保证高宽比和原始的比例一样。