如何计算UIImage的平均颜色？ [英] How to calculate the average color of a UIImage?
问题描述
我想建立一个应用程式，让使用者选取图片并输出「平均颜色」。
例如，此图片：
平均颜色是绿色/淡黄色。 / p>
此时，我收到了以下代码：
//一个UIColor扩展
public static func fromImage（image：UIImage） - > UIColor {
var totalR：CGFloat = 0
var totalG：CGFloat = 0
var totalB：CGFloat = 0
var count：CGFloat = 0
for x in 0 ..< Int（image.size.width）{
for y in 0 ..< Int（image.size.height）{
count + = 1
var rF：CGFloat = 0，
gF：CGFloat = 0，
bF：CGFloat = 0，
aF：CGFloat = 0
image.getPixelColor x：x，y：y））。getRed（& rF，green：& gF，blue：& bF，alpha：& aF）
totalR + = rF
totalG + = gF
totalB + = bF
}
}
let averageR = totalR / count
let averageG = totalG / count
let averageB = totalB / count
return UIColor（red：averageR，green：averageG，blue：averageB，alpha：1.0）
}
其中 getPixelColor 定义为：
extension UIImage {
func getPixelColor（pos：CGPoint） - > UIColor {
let pixelData = CGDataProviderCopyData（CGImageGetDataProvider（self.CGImage））
let data：UnsafePointer< UInt8> = CFDataGetBytePtr（pixelData）
让pixelInfo：Int =（（Int（self.size.width）* Int（pos.y））+ Int（pos.x））* 4
let r = CGFloat（data [pixelInfo]）/ CGFloat（255.0）
let g = CGFloat（data [pixelInfo + 1]）/ CGFloat（255.0）
let b = CGFloat [pixelInfo + 2]）/ CGFloat（255.0）
let a = CGFloat（data [pixelInfo + 3]）/ CGFloat（255.0）
return UIColor（red：r，green：g ，blue：b，alpha：a）
}
}
可以看到，我在这里做的是天真的：我循环通过图像中的所有像素，添加他们的RGBs，并除以计数。
当我运行应用程序并选择图像时，应用程序会冻结。我知道这是因为图像太大，并且两个嵌套的for循环执行了太多次。
我想找到一种有效地获得平均颜色的方法的图像。
您将需要使用Accelerate库，Apple有一个手册包含一些示例代码，它将在Swift或ObjC中工作
这里是一个让你去的示例，我用它来计算一个人的心率和心率变异性，使用颜色的变化
这是在旧版本的Swift，但我想你会得到的想法。
这里的相关代码：
//计算reg，green，blue和total的亮度
//从像素中取出颜色值--- image是BGRA
var greenVector： Float] = Array（count：numberOfPixels，repeatedValue：0.0）
var blueVector：[Float] = Array（count：numberOfPixels，repeatedValue：0.0）
var redVector：[Float] = Array（count：numberOfPixels ，repeatedValue：0.0）
vDSP_vfltu8（dataBuffer，4，& blueVector，1，vDSP_Length（numberOfPixels））
vDSP_vfltu8（dataBuffer + 1,4，& greenVector，1，vDSP_Length numberOfPixels））
vDSP_vfltu8（dataBuffer + 2，4，& redVector，1，vDSP_Length（numberOfPixels））
//计算每种颜色的平均值
var redAverage：Float = 0.0
var blueAverage：Float = 0.0
var greenAverage：Float = 0.0
vDSP_meamgv（& redVector，1，& redAverage，vDSP_Length numberOfPixels））
vDSP_meamgv（& greenVector，1，& greenAverage，vDSP_Length（numberOfPixels））
vDSP_meamgv（& blueVector，1，& blueAverage，vDSP_Length（numberOfPixels））
//转换为HSV（色相，饱和度，值）
//这样可以得到更快，更准确的答案
var hue：CGFloat = 0.0
var saturation：CGFloat = 0.0
var brightness：CGFloat = 0.0
var alpha：CGFloat = 1.0
var color：UIColor = UIColor（red：CGFloat（redAverage / 255.0），绿色：CGFloat（greenAverage / 255.0），蓝色：CGFloat（blueAverage / 255.0），alpha：alpha）
color.getHue（& hue，saturation：& saturation，brightness：& brightness，alpha： alpha）
// 5计数滚动平均值
let currentHueAverage = hue / movingAverageCount
movingAverageArray.removeAtIndex（0）
moveAverageArray.append（currentHueAverage）
让moveAverage = movingAverageArray [0] + movingAverageArray [1] + movingAverageArray [2] + movingAverageArray [3] + movingAverageArray [4]
I want to build an app that lets the user select an image and it outputs the "average color".
For example, this image:
The average color would be a greenish/yellowish color.
At the moment, I got this code:
// In a UIColor extension
public static func fromImage(image: UIImage) -> UIColor {
var totalR: CGFloat = 0
var totalG: CGFloat = 0
var totalB: CGFloat = 0
var count: CGFloat = 0
for x in 0..<Int(image.size.width) {
for y in 0..<Int(image.size.height) {
count += 1
var rF: CGFloat = 0,
gF: CGFloat = 0,
bF: CGFloat = 0,
aF: CGFloat = 0
image.getPixelColor(CGPoint(x: x, y: y)).getRed(&rF, green: &gF, blue: &bF, alpha: &aF)
totalR += rF
totalG += gF
totalB += bF
}
}
let averageR = totalR / count
let averageG = totalG / count
let averageB = totalB / count
return UIColor(red: averageR, green: averageG, blue: averageB, alpha: 1.0)
}
Where getPixelColor is defined as:
extension UIImage {
func getPixelColor(pos: CGPoint) -> UIColor {
let pixelData = CGDataProviderCopyData(CGImageGetDataProvider(self.CGImage))
let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)
let pixelInfo: Int = ((Int(self.size.width) * Int(pos.y)) + Int(pos.x)) * 4
let r = CGFloat(data[pixelInfo]) / CGFloat(255.0)
let g = CGFloat(data[pixelInfo+1]) / CGFloat(255.0)
let b = CGFloat(data[pixelInfo+2]) / CGFloat(255.0)
let a = CGFloat(data[pixelInfo+3]) / CGFloat(255.0)
return UIColor(red: r, green: g, blue: b, alpha: a)
}
}
As you can see, what I did here is pretty naive: I loop through all the pixels in the image, add their RGBs up, and divide by the count.
When I run the app and selects the image, the app freezes. I know that this is because the image is too large and the two nested for loops are executed too many times.
I want to find a way to efficiently get the average color of an image. How do I do that?
You'll need to use the Accelerate Library, Apple has a manual with some sample code, it'll work in Swift or ObjC
Here is a sample to get you going, I use this to calculate a person's heart rate and heart rate variability using the change in colors of a finger over the camera lens.
Full code here: https://github.com/timestocome/SwiftHeartRate/blob/master/Swift%20Pulse%20Reader/ViewController.swift
It's in an older version of Swift but I think you'll get the idea. I was doing this at 240 fps, but with a cropped smaller section of the image.
Relevant code here:
// compute the brightness for reg, green, blue and total
// pull out color values from pixels --- image is BGRA
var greenVector:[Float] = Array(count: numberOfPixels, repeatedValue: 0.0)
var blueVector:[Float] = Array(count: numberOfPixels, repeatedValue: 0.0)
var redVector:[Float] = Array(count: numberOfPixels, repeatedValue: 0.0)
vDSP_vfltu8(dataBuffer, 4, &blueVector, 1, vDSP_Length(numberOfPixels))
vDSP_vfltu8(dataBuffer+1, 4, &greenVector, 1, vDSP_Length(numberOfPixels))
vDSP_vfltu8(dataBuffer+2, 4, &redVector, 1, vDSP_Length(numberOfPixels))
// compute average per color
var redAverage:Float = 0.0
var blueAverage:Float = 0.0
var greenAverage:Float = 0.0
vDSP_meamgv(&redVector, 1, &redAverage, vDSP_Length(numberOfPixels))
vDSP_meamgv(&greenVector, 1, &greenAverage, vDSP_Length(numberOfPixels))
vDSP_meamgv(&blueVector, 1, &blueAverage, vDSP_Length(numberOfPixels))
// convert to HSV ( hue, saturation, value )
// this gives faster, more accurate answer
var hue: CGFloat = 0.0
var saturation: CGFloat = 0.0
var brightness: CGFloat = 0.0
var alpha: CGFloat = 1.0
var color: UIColor = UIColor(red: CGFloat(redAverage/255.0), green: CGFloat(greenAverage/255.0), blue: CGFloat(blueAverage/255.0), alpha: alpha)
color.getHue(&hue, saturation: &saturation, brightness: &brightness, alpha: &alpha)
// 5 count rolling average
let currentHueAverage = hue/movingAverageCount
movingAverageArray.removeAtIndex(0)
movingAverageArray.append(currentHueAverage)
let movingAverage = movingAverageArray[0] + movingAverageArray[1] + movingAverageArray[2] + movingAverageArray[3] + movingAverageArray[4]
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