我们知道图片的格式有很多种，如主流的png，jpg。这些格式指什么呢，指的是对图片的bitemap裸数据的压缩格式，压缩格式和压缩百分比的不同会导致图像大小和质量有差别。
说到bitmap，bitemap是什么呢？bitmap就是由一个一个像素组成的，每个像素又有可以看作是一个color，例如一张3024x4032的图片，转成bitemap之后有多大呢？一个像素大小为4个字节(rbga)，得大小为：46M,而原图片大小一般为2M左右，增大了足足23倍，由此可见压缩格式的重要性。
知道了bitmap是什么，下面来看看，如何将一张图片转成bitmap或者UIColor的数组
这里提供两种方法：
方法一：通过CGImage的dataProvider
func pixelsOfImage(_ image: UIImage) -> [[UIColor]] {
// 转CGImage
guard let inputCGImage = image.cgImage else {
return []
}
var bitmapData = inputCGImage.dataProvider!.data! as Data
// 图片宽
let width = inputCGImage.width
// 图片高
let height = inputCGImage.height
let pixels = bitmapData.withUnsafeMutableBytes { (bytes: UnsafeMutablePointer<UInt8>) -> UnsafeMutablePointer<UInt8> in
return bytes
}
var currentPixel = pixels
// 图片通道模型
var colors: [[UIColor]] = []
for _ in 0 ..< height
{
var rowColors: [UIColor] = []
for _ in 0 ..< width
{
let r = currentPixel.pointee
let g = (currentPixel + 1).pointee
let b = (currentPixel + 2).pointee
let a = (currentPixel + 3).pointee
let color = UIColor(red: CGFloat(r)/255.0, green: CGFloat(g)/255.0, blue: CGFloat(b)/255.0, alpha: CGFloat(a)/255.0)
rowColors.append(color)
currentPixel += 4
}
colors.append(rowColors)
}
return colors
}
方法二：通过CGContext生成像素数据
func pixelsOfImage1(_ image: UIImage) -> [[UIColor]] {
// 转CGImage
guard let inputCGImage = image.cgImage else {
return []
}
// 图片宽
let width = inputCGImage.width
// 图片高
let height = inputCGImage.height
// 每像素字节数 32位图为4
let bytesPerPixel = 4
// 每个颜色通道大小
let bitsPerComponent = 8
// 每行大小
let bytesPerRow = bytesPerPixel * width
let pixels = UnsafeMutablePointer<UInt8>.allocate(capacity: width * height * bytesPerPixel)
// 创建一个RGB模式的颜色空间CGColorSpace
let colorSpace = CGColorSpaceCreateDeviceRGB()
// 创建CGBitmapContext容器,将像素指针参数传递到容器中缓存进行存储。
let context = CGContext(data: pixels, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
// 绘制
context?.draw(inputCGImage, in: CGRect(x: 0, y: 0, width: CGFloat(width), height: CGFloat(height)))
var currentPixel = pixels
// 图片通道模型
var colors: [[UIColor]] = []
for _ in 0 ..< height
{
var rowColors: [UIColor] = []
for _ in 0 ..< width
{
let r = currentPixel.pointee
let g = (currentPixel + 1).pointee
let b = (currentPixel + 2).pointee
let a = (currentPixel + 3).pointee
let color = UIColor(red: CGFloat(r)/255.0, green: CGFloat(g)/255.0, blue: CGFloat(b)/255.0, alpha: CGFloat(a)/255.0)
rowColors.append(color)
currentPixel += 4
}
colors.append(rowColors)
}
return colors
}
那么又如何将bitemap数据转回去一张图片呢
func imageOfColors(_ colors: [[UIColor]]) -> UIImage {
let rows = colors.count
let cols = colors.first!.count
let totalCount = rows * cols
let pixelBytes = UnsafeMutablePointer<UInt8>.allocate(capacity: totalCount * 4)
//一个一个写进去rgba
//当前指针
var currentPoint = pixelBytes
for row in 0 ..< rows
{
for col in 0 ..< cols
{
let color = colors[row][col]
let rgba = color.cgColor.components
//rgba
for i in 0 ..< 4
{
(currentPoint + i).pointee = UInt8(rgba![i] * 255)
}
currentPoint += 4
}
}
//将bytes转化为image
let colorSpace = CGColorSpaceCreateDeviceRGB()
let ctx = CGContext.init(data: pixelBytes, width: cols, height: rows, bitsPerComponent: 8, bytesPerRow: 4 * cols, space: colorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
let cgimg = ctx!.makeImage()
pixelBytes.deallocate()
return UIImage(cgImage: cgimg!)
}
我们可以利用上诉的一些方法去做一些事情，例如：如何将鸭子的黄色颜色部分变为红色？
看看效果图：
IMG_6886.jpg
IMG_6887.jpg
