快速获取UIImage的平均颜色

I was recently attempting to convert the code from here into Swift. However, I keep getting a white color, no matter the image. Here's my code:

我最近试图将代码从这里转换为Swift。然而，无论图像是什么，我总是得到一个白色。这是我的代码:

// Playground - noun: a place where people can play

import UIKit

extension UIImage {
    func averageColor() -> UIColor {
        var colorSpace = CGColorSpaceCreateDeviceRGB()
        var rgba: [CGFloat] = [0,0,0,0]
        var context = CGBitmapContextCreate(&rgba, 1, 1, 8, 4, colorSpace, CGBitmapInfo.fromRaw(CGImageAlphaInfo.PremultipliedLast.toRaw())!)
        rgba

        CGContextDrawImage(context, CGRectMake(0, 0, 1, 1), self.CGImage)

        if rgba[3] > 0 {
            var alpha = rgba[3] / 255
            var multiplier = alpha / 255
            return UIColor(red: rgba[0] * multiplier, green: rgba[1] * multiplier, blue: rgba[2] * multiplier, alpha: alpha)
        } else {
            return UIColor(red: rgba[0] / 255, green: rgba[1] / 255, blue: rgba[2] / 255, alpha: rgba[3] / 255)
        }
    }
}

var img = UIImage(data: NSData(contentsOfURL: NSURL(string: "http://upload.wikimedia.org/wikipedia/commons/c/c3/Aurora_as_seen_by_IMAGE.PNG")))

img.averageColor()

Thanks in advance.

提前谢谢。

5 个解决方案

#1

CoreImage in iOS 9: use the CIAreaAverage filter and pass the extent of your entire image to be averaged.

ios9中的CoreImage:使用CIAreaAverage过滤器，传递要平均的整个图像范围。

Plus, it's much faster since it'll either be running on the GPU or as a highly-optimized CPU CIKernel.

另外，它速度更快，因为它可以在GPU上运行，也可以作为高度优化的CPU CIKernel运行。

#2

import UIKit

extension UIImage {
    func areaAverage() -> UIColor {
        var bitmap = [UInt8](count: 4, repeatedValue: 0)

        if #available(iOS 9.0, *) {
            // Get average color.
            let context = CIContext()
            let inputImage = CIImage ?? CoreImage.CIImage(CGImage: CGImage!)
            let extent = inputImage.extent
            let inputExtent = CIVector(x: extent.origin.x, y: extent.origin.y, z: extent.size.width, w: extent.size.height)
            let filter = CIFilter(name: "CIAreaAverage", withInputParameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: inputExtent])!
            let outputImage = filter.outputImage!
            let outputExtent = outputImage.extent
            assert(outputExtent.size.width == 1 && outputExtent.size.height == 1)

            // Render to bitmap.
            context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: kCIFormatRGBA8, colorSpace: CGColorSpaceCreateDeviceRGB())
        } else {
            // Create 1x1 context that interpolates pixels when drawing to it.
            let context = CGBitmapContextCreate(&bitmap, 1, 1, 8, 4, CGColorSpaceCreateDeviceRGB(), CGBitmapInfo.ByteOrderDefault.rawValue | CGImageAlphaInfo.PremultipliedLast.rawValue)!
            let inputImage = CGImage ?? CIContext().createCGImage(CIImage!, fromRect: CIImage!.extent)

            // Render to bitmap.
            CGContextDrawImage(context, CGRect(x: 0, y: 0, width: 1, height: 1), inputImage)
        }

        // Compute result.
        let result = UIColor(red: CGFloat(bitmap[0]) / 255.0, green: CGFloat(bitmap[1]) / 255.0, blue: CGFloat(bitmap[2]) / 255.0, alpha: CGFloat(bitmap[3]) / 255.0)
        return result
    }
}

Swift 3

斯威夫特3

func areaAverage() -> UIColor {
        var bitmap = [UInt8](repeating: 0, count: 4)

        if #available(iOS 9.0, *) {
            // Get average color.
            let context = CIContext()
            let inputImage: CIImage = ciImage ?? CoreImage.CIImage(cgImage: cgImage!)
            let extent = inputImage.extent
            let inputExtent = CIVector(x: extent.origin.x, y: extent.origin.y, z: extent.size.width, w: extent.size.height)
            let filter = CIFilter(name: "CIAreaAverage", withInputParameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: inputExtent])!
            let outputImage = filter.outputImage!
            let outputExtent = outputImage.extent
            assert(outputExtent.size.width == 1 && outputExtent.size.height == 1)

            // Render to bitmap.
            context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: kCIFormatRGBA8, colorSpace: CGColorSpaceCreateDeviceRGB())
        } else {
            // Create 1x1 context that interpolates pixels when drawing to it.
            let context = CGContext(data: &bitmap, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: CGColorSpaceCreateDeviceRGB(), bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!
            let inputImage = cgImage ?? CIContext().createCGImage(ciImage!, from: ciImage!.extent)

            // Render to bitmap.
            context.draw(inputImage!, in: CGRect(x: 0, y: 0, width: 1, height: 1))
        }

        // Compute result.
        let result = UIColor(red: CGFloat(bitmap[0]) / 255.0, green: CGFloat(bitmap[1]) / 255.0, blue: CGFloat(bitmap[2]) / 255.0, alpha: CGFloat(bitmap[3]) / 255.0)
        return result
    }

#3

Here's a solution:

这里有一个解决方案:

func averageColor() -> UIColor {

    let rgba = UnsafeMutablePointer<CUnsignedChar>.alloc(4)
    let colorSpace: CGColorSpaceRef = CGColorSpaceCreateDeviceRGB()
    let info = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)
    let context: CGContextRef = CGBitmapContextCreate(rgba, 1, 1, 8, 4, colorSpace, info)

    CGContextDrawImage(context, CGRectMake(0, 0, 1, 1), self.CGImage)

    if rgba[3] > 0 {

        let alpha: CGFloat = CGFloat(rgba[3]) / 255.0
        let multiplier: CGFloat = alpha / 255.0

        return UIColor(red: CGFloat(rgba[0]) * multiplier, green: CGFloat(rgba[1]) * multiplier, blue: CGFloat(rgba[2]) * multiplier, alpha: alpha)

    } else {

        return UIColor(red: CGFloat(rgba[0]) / 255.0, green: CGFloat(rgba[1]) / 255.0, blue: CGFloat(rgba[2]) / 255.0, alpha: CGFloat(rgba[3]) / 255.0)
    }
}

#4

Swift 3:

斯威夫特3:

func areaAverage() -> UIColor {

    var bitmap = [UInt8](repeating: 0, count: 4)

    let context = CIContext(options: nil)
    let cgImg = context.createCGImage(CoreImage.CIImage(cgImage: self.cgImage!), from: CoreImage.CIImage(cgImage: self.cgImage!).extent)

    let inputImage = CIImage(cgImage: cgImg!)
    let extent = inputImage.extent
    let inputExtent = CIVector(x: extent.origin.x, y: extent.origin.y, z: extent.size.width, w: extent.size.height)
    let filter = CIFilter(name: "CIAreaAverage", withInputParameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: inputExtent])!
    let outputImage = filter.outputImage!
    let outputExtent = outputImage.extent
    assert(outputExtent.size.width == 1 && outputExtent.size.height == 1)

    // Render to bitmap.
    context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: kCIFormatRGBA8, colorSpace: CGColorSpaceCreateDeviceRGB())

    // Compute result.
    let result = UIColor(red: CGFloat(bitmap[0]) / 255.0, green: CGFloat(bitmap[1]) / 255.0, blue: CGFloat(bitmap[2]) / 255.0, alpha: CGFloat(bitmap[3]) / 255.0)
    return result
}

#5

Are you setting up your context correctly? If I look at the documentation for the CGBitmapContext Reference:

你的上下文设置是否正确?如果我查看CGBitmapContext引用的文档:

https://developer.apple.com/library/ios/documentation/graphicsimaging/Reference/CGBitmapContext/index.html#//apple_ref/c/func/CGBitmapContextCreate

https://developer.apple.com/library/ios/documentation/graphicsimaging/Reference/CGBitmapContext/index.html / / apple_ref / c /函数/ CGBitmapContextCreate

it looks like you are only allocating enough memory for the image that would be contained in the CGFloat array. It also looks like you are telling the compiler that your image is only going to be one pixel by one pixel.

看起来您只是为CGFloat数组中包含的映像分配了足够的内存。看起来你也在告诉编译器你的图像将会是一个像素一个像素。

It looks like that size is also being confirmed as one pixel by one pixel when you are setting your CGRect in CGContextDrawImage.

当你在CGContextDrawImage中设置CGRect时，这个大小看起来也被一个像素一个像素地确定了。

If the Playground is only creating an image one pixel by one pixel, that would explain why you are only seeing a white screen.

如果游乐场只创建一个像素一个像素的图像，这就可以解释为什么你只看到一个白色的屏幕。