需求：传入颜色数组、图片宽高、行列数，生成像素图片。

生成的图片

/// 生成随机颜色
extension UIColor {
    static var random: Color {
        let red = Int.random(in: 0...255)
        let green = Int.random(in: 0...255)
        let blue = Int.random(in: 0...255)
        return Color(red: red, green: green, blue: blue)!
    }
}

// 传一个颜色数组
let column: Int = 3
let row: Int = 2
let scale: CGFloat = 100

var randomColors: [UIColor] = []
for _ in 0..<column * row {
    randomColors.append(UIColor.random)
}
imageView.image = UIImage.pixelImage(with: randomColors,
                   size: CGSize(width: CGFloat(column) * scale, height: CGFloat(row) * scale),
                   col: column, row: row)

lazy var imageView: UIImageView = {
   let iv = UIImageView(frame: CGRect(x: 0, y: 0, width: 300, height: 200))
   view.addSubview(iv)
   return iv
}()

用 UIGraphics 绘制，注意 size 与行列数的关系

extension UIImage {
    /// 根据传入的颜色数组生成对应像素图
    /// - Parameters:
    ///   - colors: 颜色数组
    ///   - size: 生成的 UIImage 大小
    ///   - col: 列
    ///   - row: 行
    ///   - haveline: 是否绘制分割线，默认不绘
    static func pixelImage(with colors: [UIColor], size: CGSize, column: Int, row: Int, haveline: Bool = false) -> UIImage {
        var i = UIImage()
        if size.width == 0 || size.height == 0 {
            return i
        }
        
        if colors.count != column * row {
            return i
        }
        
        let allRect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
        UIGraphicsBeginImageContextWithOptions(allRect.size, false, 0.0)
        let context = UIGraphicsGetCurrentContext()!
        
        
        let signleWidth: CGFloat = size.width / CGFloat(column)
        let signleHeight: CGFloat = size.height / CGFloat(row)
        
        var x: CGFloat = 0
        var y: CGFloat = 0
        var index = 0
        
        for _ in 0..<row {
            for _ in 0..<column {
                let rect = CGRect(x: x, y: y, width: signleWidth, height: signleHeight)
                context.setFillColor(colors[index].cgColor)
                context.fill(rect)
                
                index += 1
                x += signleWidth
            }
            x = 0
            y += signleHeight
        }
        
        if haveline {
            let path = CGMutablePath()
            for i in 0...row {
                path.move(to: CGPoint(x: 0, y: signleHeight * CGFloat(i)))
                path.addLine(to: CGPoint(x: size.width, y: signleHeight * CGFloat(i)))
            }
            for i in 0...column {
                path.move(to: CGPoint(x: signleWidth * CGFloat(i), y: 0))
                path.addLine(to: CGPoint(x: signleWidth * CGFloat(i), y: size.height))
            }
            context.addPath(path)
            context.setStrokeColor(UIColor.hex(0x999999).cgColor)
            context.setLineWidth(0.2)
            context.strokePath()
        }
        
        i = UIGraphicsGetImageFromCurrentImageContext() ?? UIImage()
        UIGraphicsEndImageContext()
        return i
    }
}