Swift3 - 使用 CoreGraphics 或 CoreImage 从图像中裁剪或修剪无聊的像素答案

【问题标题】：Swift3 - Crop-out or trim boring pixels from the image with CoreGraphics or CoreImageSwift3 - 使用 CoreGraphics 或 CoreImage 从图像中裁剪或修剪无聊的像素
【发布时间】：2016-10-20 10:16:47
【问题描述】：

我想知道是否有一种简单的方法可以使用 CoreGraphics 或 CoreImage 和 Swift3 修剪/裁剪图像？

给定顶部的输入图像（带有红色/玫瑰色背景），我们将这些红色像素修剪掉，只留下真实的、有趣的部分？

【问题讨论】：

标签： macos core-graphics swift3 core-image

【解决方案1】：

我刚刚在这里回答了一个类似问题的一个子集：Iterate over individual pixels of a UIImage with height information

以下是获取顶部和底部唯一像素的方法。

    func pixelNotMatchingTopLeftColor(in image: UIImage, first isFirst: Bool) -> CGPoint? {
        let width = Int(image.size.width)
        let height = Int(image.size.height)
        guard width > 1 || height < 1 else {
            return nil
        }
        if let cfData:CFData = image.cgImage?.dataProvider?.data, let pointer = CFDataGetBytePtr(cfData) {
            let cornerPixelRed = pointer.pointee
            let cornerPixelGreen = pointer.advanced(by: 0).pointee
            let cornerPixelBlue = pointer.advanced(by: 1).pointee
            let cornerPixelAlpha = pointer.advanced(by: 2).pointee
            let bytesPerpixel = 4
            let firstPixel = 1 * bytesPerpixel
            let lastPixel = width * height * bytesPerpixel - 1 * bytesPerpixel
            let range = isFirst ? stride(from: firstPixel, through: lastPixel, by: bytesPerpixel) :
                                  stride(from: lastPixel, through: firstPixel + bytesPerPixel, by: -bytesPerpixel)
            for pixelAddress in range {
                    if pointer.advanced(by: pixelAddress).pointee != cornerPixelRed ||     //Red
                       pointer.advanced(by: pixelAddress + 1).pointee != cornerPixelGreen || //Green
                       pointer.advanced(by: pixelAddress + 2).pointee != cornerPixelBlue || //Blue
                       pointer.advanced(by: pixelAddress + 3).pointee != cornerPixelAlpha  {  //Alpha
                        print(pixelAddress)
                        return CGPoint(x: (pixelAddress / bytesPerpixel) % width, y: (pixelAddress / bytesPerpixel) / width)
                    }
                }
        }
        return nil
    }

    func firstUniquePixel( in image: UIImage) -> CGPoint?  {
        return pixelNotMatchingTopLeftColor(in: image, first: true)
    }

    func lastUniquePixel( in image: UIImage) -> CGPoint?  {
        return pixelNotMatchingTopLeftColor(in: image, first: false)
    }

您必须为左右做类似的事情（如果您在计算指针数学时遇到问题，请告诉我）。然后使用 top、left、bottom 和 right 你只需调用 CGImageCreateWithImageInRect。

【讨论】：