What causes "Invalid PLTE chunk length." in OpenRA/OpenRA?

Re-export the PNG from the original indexed-color source image.

OpenRA/OpenRA · error · InvalidDataException

Invalid PLTE chunk length.

Error message

Invalid PLTE chunk length.

What it means

Thrown by Png(Stream) when a PLTE (palette) chunk's declared length is not evenly divisible by 3. Each palette entry is an RGB triplet (3 bytes), so the total length must be length % 3 == 0. A non-multiple-of-3 length means the palette data is malformed.

Source

Thrown at OpenRA.Game/FileFormats/Png.cs:184

						if (compression != 0)
							throw new InvalidDataException("Compression method not supported");

						if (interlace != 0)
							throw new InvalidDataException("Interlacing not supported");

						Data = new byte[Width * Height * PixelStride];

						// Skip CRC.
						s.Seek(4, SeekOrigin.Current);
						headerParsed = true;
						break;
					}

					case ChunkPLTE:
					{
						if (length % 3 != 0)
							throw new InvalidDataException("Invalid PLTE chunk length.");

						var count = length / 3;
						Palette = new Color[count];

						var buffer = ArrayPool<byte>.Shared.Rent(length);
						try
						{
							s.ReadBytes(buffer.AsSpan(0, length));
							for (var i = 0; i < count; i++)
							{
								var offset = i * 3;
								Palette[i] = Color.FromArgb(buffer[offset], buffer[offset + 1], buffer[offset + 2]);
							}
						}
						finally
						{
							ArrayPool<byte>.Shared.Return(buffer);
						}

View on GitHub (pinned to a520984d91)

Solutions

Re-export the PNG from the original indexed-color source image.
Run pngcheck to validate palette chunk integrity.
Replace the corrupt file with a clean copy from version control or backup.

Defensive patterns

Strategy: try-catch

Try / catch

try
{
    var png = new Png(stream);
}
catch (InvalidDataException ex) when (ex.Message.Contains("PLTE chunk length"))
{
    logger.LogError($"Corrupt PNG palette: {ex.Message}");
}

Prevention

Re-export indexed PNGs from source images rather than manually editing palette data.
Run pngcheck on all indexed PNG assets during CI.
Store original source images (e.g., PSD, XCF) to regenerate assets if corruption occurs.

When it happens

Trigger: Constructing `new Png(stream)` where an indexed-color PNG has a PLTE chunk whose 4-byte big-endian length field is not divisible by 3. The code checks `length % 3 != 0` immediately upon encountering ChunkPLTE.

Common situations: Byte-level corruption in the PLTE chunk's length field. A broken PNG encoder that wrote an incorrect length. File truncation or modification that shifted bytes within the PLTE chunk.

Related errors

AI-assisted analysis of OpenRA/OpenRA@a520984d91 (2026-08-13). Data as JSON: /api/errors/0b57b571c67bee48. Report an issue: GitHub.