SixLabors/ImageSharp · error · InvalidImageContentException

APNG Image does not contain a default data chunk.

Error message

APNG Image does not contain a default data chunk.

What it means

Thrown when decoding an APNG (animated PNG) that declares animation but lacks the default image data chunk (IDAT, or an fdAT with sequence number 0 acting as the default frame). The APNG spec requires a default image that all frames are composited over.

Solutions

  1. Re-generate the APNG ensuring a valid default image (IDAT with preceding fcTL of seq 0) is present.
  2. Re-encode the animation with a spec-compliant tool (e.g. ffmpeg -plays 0 output, apngasm).
  3. If a still image is expected, check whether the input is really an APNG and decode the intended variant.
  4. Catch InvalidImageContentException to fall back to alternative handling.

Example fix

// before (ffmpeg, missing default image)
ffmpeg -i frames%d.png -plays 0 out.png
// after
ffmpeg -i frame0.png -i frames%d.png -plays 0 out.png // frame0 supplies the default IDAT
Defensive patterns

Strategy: validation

Try / catch

try
{
    using var image = Image.Load(stream);
}
catch (InvalidImageContentException ex) when (ex.Message.Contains("default data chunk"))
{
    // malformed APNG — fall back to an alternate source or placeholder
}

Prevention

When it happens

Trigger: Decoding an APNG containing acTL and fcTL/fdAT chunks but no default image data; files where the default frame's fcTL and IDAT were stripped while animation metadata remained.

Common situations: APNGs produced by tools that only emit animation frames, files edited to remove the still image but not the animation metadata, corrupted animation exports.

Related errors

AI-assisted analysis of SixLabors/ImageSharp@59ce6af6fc (2026-09-13). Data as JSON: /api/errors/10465d652af7f491. Report an issue: GitHub.

Appendix: source

Thrown at src/ImageSharp/Formats/Png/PngThrowHelper.cs:21

using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;

namespace SixLabors.ImageSharp.Formats.Png;

internal static class PngThrowHelper
{
    [DoesNotReturn]
    public static void ThrowInvalidImageContentException(string errorMessage) => throw new InvalidImageContentException(errorMessage);

    [DoesNotReturn]
    public static void ThrowInvalidHeader() => throw new InvalidImageContentException("PNG Image must contain a header chunk and it must be located before any other chunks.");

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

    [DoesNotReturn]
    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!");

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