LoadPreservedPixelType

LoadPreservedPixelType.cs

static Image LoadPreservePixelType(string path)
{
    var info   = Image.Identify(path);
    var format = info.Metadata.DecodedImageFormat;

    // PNG: PngColorType fully describes the pixel layout including alpha
    if (format is PngFormat)  return LoadPng(path, info);

    // BMP, TGA: native channel order is BGR/BGRA
    if (format is BmpFormat)  return LoadBmp(path, info);
    if (format is TgaFormat)  return LoadTga(path, info);

    // TIFF, JPEG, WebP, GIF, QOI, PBM, etc.
    // AlphaRepresentation is not populated by Image.Identify in 3.1.x, so we
    // rely on BitsPerPixel only. TIFF limitation: La16/La32 are indistinguishable
    // from L16/Rgba32 without photometric interpretation metadata.
    return info.PixelType.BitsPerPixel switch
    {
        8  => Image.Load<L8>(path),
        16 => Image.Load<L16>(path),
        24 => Image.Load<Rgb24>(path),
        32 => Image.Load<Rgba32>(path),
        48 => Image.Load<Rgb48>(path),
        64 => Image.Load<Rgba64>(path),
        _  => Image.Load(path)
    };
    
    static Image LoadPng(string path, ImageInfo info)
    {
        var meta = info.Metadata.GetPngMetadata();
        return (meta.ColorType, info.PixelType.BitsPerPixel) switch
        {
            (PngColorType.Grayscale,          8)  => Image.Load<L8>(path),
            (PngColorType.Grayscale,         16)  => Image.Load<L16>(path),
            (PngColorType.GrayscaleWithAlpha, 16) => Image.Load<La16>(path),
            (PngColorType.GrayscaleWithAlpha, 32) => Image.Load<La32>(path),
            (PngColorType.Rgb,               24)  => Image.Load<Rgb24>(path),
            (PngColorType.Rgb,               48)  => Image.Load<Rgb48>(path),
            (PngColorType.RgbWithAlpha,      32)  => Image.Load<Rgba32>(path),
            (PngColorType.RgbWithAlpha,      64)  => Image.Load<Rgba64>(path),
            _                                     => Image.Load(path)  // Palette, exotic
        };
    }

    static Image LoadBmp(string path, ImageInfo info) =>
        info.Metadata.GetBmpMetadata().BitsPerPixel switch
        {
            BmpBitsPerPixel.Pixel16 => Image.Load<Bgr565>(path),
            BmpBitsPerPixel.Pixel24 => Image.Load<Bgr24>(path),
            BmpBitsPerPixel.Pixel32 => Image.Load<Bgra32>(path),
            _                       => Image.Load(path)  // Pixel1/2/4/8: palette/indexed
        };

    static Image LoadTga(string path, ImageInfo info) =>
        info.Metadata.GetTgaMetadata().BitsPerPixel switch
        {
            TgaBitsPerPixel.Pixel8  => Image.Load<L8>(path),
            TgaBitsPerPixel.Pixel16 => Image.Load<Bgra5551>(path),  // 5+5+5+1
            TgaBitsPerPixel.Pixel24 => Image.Load<Bgr24>(path),
            TgaBitsPerPixel.Pixel32 => Image.Load<Bgra32>(path),
            _                       => Image.Load(path)
        };
}