在没有内存峰值的情况下旋转UIImage

Question

我目前正在使用旋转图像CGContextDrawImage,但无论何时调用它都会有一个巨大的内存峰值.较新的设备可以处理它,但是具有较低内存的设备(例如iPhone 4s)则不能.该图像是用户在的大文件AVCaptureSessionPresetHigh

我正在使用此扩展名来旋转图像 UIImage

func rotate(orientation: UIImageOrientation) -> UIImage{
    if(orientation == UIImageOrientation.Up){return self}

    var transform: CGAffineTransform = CGAffineTransformIdentity

    if(orientation == UIImageOrientation.Down || orientation == UIImageOrientation.DownMirrored){
        transform = CGAffineTransformTranslate(transform, self.size.width, self.size.height)
        transform = CGAffineTransformRotate(transform, CGFloat(M_PI))
    }
    else if(orientation == UIImageOrientation.Left || orientation == UIImageOrientation.LeftMirrored){
        transform = CGAffineTransformTranslate(transform, self.size.width, 0)
        transform = CGAffineTransformRotate(transform, CGFloat(M_PI_2))
    }
    else if(orientation == UIImageOrientation.Right || orientation == UIImageOrientation.RightMirrored){
        transform = CGAffineTransformTranslate(transform, 0, self.size.height)
        transform = CGAffineTransformRotate(transform,  CGFloat(-M_PI_2))
    }


    if(orientation == UIImageOrientation.UpMirrored || orientation == UIImageOrientation.DownMirrored){
        transform = CGAffineTransformTranslate(transform, self.size.width, 0)
        transform = CGAffineTransformScale(transform, -1, 1)
    }
    else if(orientation == UIImageOrientation.LeftMirrored || orientation == UIImageOrientation.RightMirrored){
        transform = CGAffineTransformTranslate(transform, self.size.height, 0)
        transform = CGAffineTransformScale(transform, -1, 1);
    }

    let ref: CGContextRef = CGBitmapContextCreate(nil, Int(self.size.width), Int(self.size.height), CGImageGetBitsPerComponent(self.CGImage), 0, CGImageGetColorSpace(self.CGImage), CGImageGetBitmapInfo(self.CGImage))
    CGContextConcatCTM(ref, transform)

    if(orientation == UIImageOrientation.Left || orientation == UIImageOrientation.LeftMirrored || orientation == UIImageOrientation.Right || orientation == UIImageOrientation.RightMirrored){
        CGContextDrawImage(ref, CGRectMake(0, 0, self.size.height, self.size.width), self.CGImage)
    }
    else{
        CGContextDrawImage(ref, CGRectMake(0, 0, self.size.width, self.size.height), self.CGImage)
    }


    let cgImg: CGImageRef = CGBitmapContextCreateImage(ref)
    let rotated: UIImage = UIImage(CGImage: cgImg)!

    return rotated
}

此代码在iPhone 5和6等设备上运行良好,但几乎总是会因为内存不足而导致iPhone 4s崩溃.

我知道我可以使用指定方向的EXIF数据上传图像,但我觉得在上传之前旋转图像可以防止进一步出现问题.

iOS如何使用EXIF数据旋转图像以进行显示？例如,虽然使用

UIImage(image.CGImage, scale: 1.0, orientation: UIImageOrientation.Right)

更改EXIF数据后,图像仍然以正确的方向显示在屏幕上,对内存的影响要小得多.是否有一些真正的低级代码可以通过像上面的代码一样使用GPU来实现这一点？

我还想避免在上传之前缩小图像.

有什么方法可以减少旋转图像的影响,例如将其旋转成碎片,还是我必须找到替代方案？

Answer 1

我能够（大部分）通过UIGraphicsEndImageContext()在上述代码末尾调用来解决这个问题，并且直到上传之前才旋转图像（用户可以在上传照片之前旋转照片，因此直到上传之前才旋转它们）大大减少了内存占用）。

因此，每当用户旋转照片时，我都会调用rotateExif(orientation)我创建的这个函数

extension UIImage{
    func rotateExif(orientation: UIImageOrientation) -> UIImage{

        if(orientation == UIImageOrientation.Up){return self}

        let current = self.imageOrientation
        let currentDegrees: Int = (
            current == UIImageOrientation.Down || current == UIImageOrientation.DownMirrored ? 180 : (
                current == UIImageOrientation.Left || current == UIImageOrientation.LeftMirrored ? 270 : (
                    current == UIImageOrientation.Right || current == UIImageOrientation.RightMirrored ? 90 : 0
                )
            )
        )
        let changeDegrees: Int = (
            orientation == UIImageOrientation.Down || orientation == UIImageOrientation.DownMirrored ? 180 : (
                orientation == UIImageOrientation.Left || orientation == UIImageOrientation.LeftMirrored ? 270 : (
                    orientation == UIImageOrientation.Right || orientation == UIImageOrientation.RightMirrored ? 90 : 0
                )
            )
        )


        let mirrored: Bool = (
            current == UIImageOrientation.DownMirrored || current == UIImageOrientation.UpMirrored ||
            current == UIImageOrientation.LeftMirrored || current == UIImageOrientation.RightMirrored ||
            orientation == UIImageOrientation.DownMirrored || orientation == UIImageOrientation.UpMirrored ||
            orientation == UIImageOrientation.LeftMirrored || orientation == UIImageOrientation.RightMirrored
        )

        let degrees: Int = currentDegrees + changeDegrees

        let newOrientation: UIImageOrientation = (
            degrees == 270 || degrees == 630 ? (mirrored ? UIImageOrientation.LeftMirrored : UIImageOrientation.Left) : (
                degrees == 180 || degrees == 540 ? (mirrored ? UIImageOrientation.DownMirrored : UIImageOrientation.Down) : (
                    degrees == 90 || degrees == 450 ? (mirrored ? UIImageOrientation.RightMirrored : UIImageOrientation.Right) : (
                        mirrored ? UIImageOrientation.UpMirrored : UIImageOrientation.Up
                    )
                )
            )
        )

        return UIImage(CGImage: self.CGImage!, scale: 1.0, orientation: newOrientation)
    }
}

这会按照 中输入的量旋转图像的 EXIF orientation。因此，例如，如果原始方向为Right，并且旋转了Right，则新方向将为Down。如果原来的方向是RightMirrored，并且旋转了它Left，则新的方向将是UpMirrored。

然后，在上传照片之前，通过调用问题中的代码作为 , 的扩展来旋转实际像素UIImage。image.rotate(image.imageOrientation)