main.swift

import PNG

let path:String         = "examples/encode-basic/example", 
    size:(x:Int, y:Int) = (800, 1228)
guard let rgba:[PNG.RGBA<UInt8>] = (System.File.Source.open(path: "\(path).rgba")
{
    guard let data:[UInt8] = $0.read(count: 4 * size.x * size.y)
    else 
    {
        fatalError("failed to read from file '\(path).rgba'")
    }

    return (0 ..< size.x * size.y).map 
    {
        (i:Int) -> PNG.RGBA<UInt8> in
        .init(data[4 * i], data[4 * i + 1], data[4 * i + 2], data[4 * i + 3])
    }
}) 
else
{
    fatalError("failed to open file '\(path).rgba'")
}

let layout:(rgb:PNG.Layout, v:PNG.Layout) = 
(
    rgb:    .init(format: .rgb8(palette: [], fill: nil, key: nil)),
    v:      .init(format:   .v8(             fill: nil, key: nil))
)

do 
{
    let image:PNG.Data.Rectangular  = .init(packing: rgba, size: size, layout: layout.rgb)
    try image.compress(path: "\(path)-color-rgb.png", level: 9)
    
    for level:Int in [0, 4, 8, 13]
    {
        try image.compress(path: "\(path)-color-rgb@\(level).png", level: level)
    }
}
do 
{
    let image:PNG.Data.Rectangular  = .init(packing: rgba, size: size, layout: layout.v)
    try image.compress(path: "\(path)-color-v.png", level: 9)
}

let luminance:[UInt8] = rgba.map 
{
    let r:Double = .init($0.r), 
        g:Double = .init($0.g),
        b:Double = .init($0.b)
    let l:Double = (0.299 * r * r + 0.587 * g * g + 0.114 * b * b).squareRoot()
    return .init(max(0, min(l.rounded(), 255)))
}
do 
{
    let image:PNG.Data.Rectangular  = .init(packing: luminance, size: size, layout: layout.v)
    try image.compress(path: "\(path)-luminance-v.png", level: 9)
}
do 
{
    let image:PNG.Data.Rectangular  = .init(packing: luminance, size: size, layout: layout.rgb)
    try image.compress(path: "\(path)-luminance-rgb.png", level: 9)
}