如何按比例缩小UIImage并使其酥脆/清晰而不是模糊？

Question

我需要按比例缩小图像，但要采用清晰的方式。例如，在Photoshop中，图像尺寸缩小选项为“ Bicubic Smoother”（模糊）和“ Bicubic Sharper”。该图像缩小算法是在某个地方开源或记录的，还是SDK提供了执行此操作的方法？

Answer 1

如果有人正在寻找Swift版本，这是@Dan Rosenstark接受的答案的Swift版本：

func resizeImage(image: UIImage, newHeight: CGFloat) -> UIImage {

    let scale = newHeight / image.size.height

    let newWidth = image.size.width * scale

    UIGraphicsBeginImageContext(CGSizeMake(newWidth, newHeight))

    image.drawInRect(CGRectMake(0, 0, newWidth, newHeight))

    let newImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return newImage

}

Answer 2

对于那些使用Swift的人，这是Swift中公认的答案：

func resizeImage(image: UIImage, newSize: CGSize) -> (UIImage) {

    let newRect = CGRectIntegral(CGRectMake(0,0, newSize.width, newSize.height))

    let imageRef = image.CGImage

    UIGraphicsBeginImageContextWithOptions(newSize, false, 0)

    let context = UIGraphicsGetCurrentContext()

    // Set the quality level to use when rescaling

    CGContextSetInterpolationQuality(context, kCGInterpolationHigh)

    let flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height)

    CGContextConcatCTM(context, flipVertical)

    // Draw into the context; this scales the image

    CGContextDrawImage(context, newRect, imageRef)

    let newImageRef = CGBitmapContextCreateImage(context) as CGImage

    let newImage = UIImage(CGImage: newImageRef)

    // Get the resized image from the context and a UIImage

    UIGraphicsEndImageContext()

    return newImage

}