Scale and Cut

代码来自stackoverflow, 测试完全可用, 缩放并不强制向下, 若想只向下缩放, 请自行调试代码

+(UIImage*)Resize:(UIImage*)sourceImage toSize:(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; // 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;
            }
        }
    }
    UIGraphicsBeginImageContext(targetSize); // this will crop
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width  = scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    [sourceImage drawInRect:thumbnailRect];
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    if(newImage == nil){
        NSLog(@"could not scale image");
    }
    //pop the context to get back to the default
    UIGraphicsEndImageContext();
    return newImage;
}