SixLabors/ImageSharp · error · InvalidImageContentException

CRC Error. PNG chunk is corrupt!

Error message

CRC Error. PNG {chunkTypeName} chunk is corrupt!

What it means

Thrown when the CRC32 checksum of a PNG chunk does not match the chunk's stored CRC value, meaning the chunk's bytes were corrupted or altered after encoding. Each PNG chunk carries a CRC over its type and data; a mismatch indicates the data is not what the encoder wrote, and the spec says decoders should treat it as a corrupted file.

Solutions

1. Re-obtain the file from its source and verify integrity (hash or CRC check) before decoding.
2. Identify the corrupt chunk from the message and repair it with a PNG repair tool that recomputes CRCs (e.g. pngcheck -f, pngfix).
3. Ensure binary-safe transfer (FTP binary mode, no text encoding of image data).
4. Catch InvalidImageContentException and treat the file as corrupted, prompting re-upload.

Example fix

// before
byte[] png = File.ReadAllBytes(path);
using var image = Image.Load(png);
// after
byte[] png = File.ReadAllBytes(path);
if (!CrcIsExpected(png)) throw new IOException("File corrupt in transit; re-download");
using var image = Image.Load(png);

// Verify transfer integrity before decoding
using (var sha = System.Security.Cryptography.SHA256.Create())
{
    var hash = sha.ComputeHash(File.ReadAllBytes(path));
    if (!hash.AsSpan().SequenceEqual(expectedHash))
        throw new IOException("File corrupt: re-download required");
}

try
{
    using var image = Image.Load(stream);
}
catch (InvalidImageContentException ex) when (ex.Message.StartsWith("CRC Error"))
{
    // corrupted chunk — prompt re-upload/re-download
}

When it happens

Trigger: Decoding any PNG where a chunk's CRC check fails — bytes modified in transit, bit rot on disk, chunk data edited without recomputing CRC, or a partially corrupted download.

Common situations: Files transferred in ASCII mode (e.g. FTP text-mode), corrupted attachments, files edited by hex editors or scripts that forgot to update the CRC, failing storage media.

Understand the failure class

Background: Checksum mismatch errors: "checksum verification failed", "digest mismatch", "expected vs actual checksum" — what they mean and how to fix them — this error's family across 41 libraries.

Related errors

• {errorMessage}
• Invalid PNG data.
• Invalid window size for ZLIB header: cinfo=
• Bad method for ZLIB header: cmf=
• Not a valid pass index

AI-assisted analysis of SixLabors/ImageSharp@59ce6af6fc (2026-09-13). Data as JSON: /api/errors/5c1cbe763e91ddd9. Report an issue: GitHub.

Appendix: source

Thrown at src/ImageSharp/Formats/Png/PngThrowHelper.cs:39

    public static void ThrowMissingDefaultData() => throw new InvalidImageContentException("APNG Image does not contain a default data chunk.");

    [DoesNotReturn]
    public static void ThrowInvalidAnimationControl() => throw new InvalidImageContentException("APNG Image must contain a acTL chunk and it must be located before any IDAT and fdAT chunks.");

    [DoesNotReturn]
    public static void ThrowMissingFrameControl() => throw new InvalidImageContentException("One of APNG Image's frames do not have a frame control chunk.");

    [DoesNotReturn]
    public static void ThrowMissingPalette() => throw new InvalidImageContentException("PNG Image does not contain a palette chunk.");

    [DoesNotReturn]
    public static void ThrowInvalidChunkType() => throw new InvalidImageContentException("Invalid PNG data.");

    [DoesNotReturn]
    public static void ThrowInvalidChunkType(string message) => throw new InvalidImageContentException(message);

    [DoesNotReturn]
    public static void ThrowInvalidChunkCrc(string chunkTypeName) => throw new InvalidImageContentException($"CRC Error. PNG {chunkTypeName} chunk is corrupt!");

    [DoesNotReturn]
    public static void ThrowInvalidParameter(object value, string message, [CallerArgumentExpression(nameof(value))] string name = "")
        => throw new NotSupportedException($"Invalid {name}. {message}. Was '{value}'.");

    [DoesNotReturn]
    public static void ThrowInvalidParameter(object value1, object value2, string message, [CallerArgumentExpression(nameof(value1))] string name1 = "", [CallerArgumentExpression(nameof(value2))] string name2 = "")
        => throw new NotSupportedException($"Invalid {name1} or {name2}. {message}. Was '{value1}' and '{value2}'.");

    [DoesNotReturn]
    public static void ThrowNotSupportedColor() => throw new NotSupportedException("Unsupported PNG color type.");

    [DoesNotReturn]
    public static void ThrowUnknownFilter() => throw new InvalidImageContentException("Unknown filter type.");
}

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