/// <summary>
/// Given an indexed line with a palette, unpacks as a RGB array
/// </summary>
/// <param name="line">ImageLine as returned from PngReader</param>
/// <param name="pal">Palette chunk</param>
/// <param name="trns">TRNS chunk (optional)</param>
/// <param name="buf">Preallocated array, optional</param>
/// <returns>R G B (one byte per sample)</returns>
public static int[] Palette2rgb(ImageLine line, PngChunkPLTE pal, PngChunkTRNS trns, int[] buf)
{
if (line is null)
{
throw new ArgumentNullException(nameof(line));
}
if (pal is null)
{
throw new ArgumentNullException(nameof(pal));
}
var isalpha = trns is object;
var channels = isalpha ? 4 : 3;
var nsamples = line.ImgInfo.Cols * channels;
if (buf is null || buf.Length < nsamples)
{
buf = new int[nsamples];
}
if (!line.SamplesUnpacked)
{
line = line.UnpackToNewImageLine();
}
var isbyte = line.SampleType == Hjg.Pngcs.ImageLine.ESampleType.BYTE;
var nindexesWithAlpha = trns?.GetPalletteAlpha().Length ?? 0;
for (var c = 0; c < line.ImgInfo.Cols; c++)
{
var index = isbyte ? (line.ScanlineB[c] & 0xFF) : line.Scanline[c];
pal.GetEntryRgb(index, buf, c * channels);
if (isalpha)
{
buf[(c * channels) + 3] = index < nindexesWithAlpha?trns.GetPalletteAlpha()[index] : 255;
}
}
return(buf);
}
