Gist tell me how bright it is

GetLuma.ps1

filter GetLuma {
    $colorString = $_
    # Convert the background color to a uint32
    $rgb = ($colorString -replace "#", "0x" -replace ';') -as [UInt32]
    # then make it into a percentage red, green, and blue.
    $r, $g, $b = ([float][byte](($rgb -band 0xff0000) -shr 16)/255),
        ([float][byte](($rgb -band 0x00ff00) -shr 8)/255),
        ([float][byte]($rgb -band 0x0000ff)/255)

    # Calculate the luma of the background color
    0.2126 * $R + 0.7152 * $G + 0.0722 * $B    
}