SixLabors/ImageSharp · error · InvalidIccProfileException

Invalid CLUT data type of

Error message

Invalid CLUT data type of {value.DataType}

What it means

When writing a CLUT, its DataType must be UInt8, UInt16, or Float32. The writer switches on the declared data type to pick the binary encoding; an unknown IccClutDataType has no on-disk representation, so the writer refuses instead of emitting garbage bytes.

Solutions

1. Set the IccClut DataType explicitly to IccClutDataType.UInt8, UInt16, or Float32 before writing.
2. Initialize IccClut via a constructor that takes the data and channel counts so DataType is derived correctly.
3. Check for invalid enum casts into IccClutDataType in your code path.

Example fix

// before: struct default leaves DataType unset
count += writer.WriteClut(new IccClut());

// after: construct with valid data and matching channel counts
var clut = new IccClut(
    inChannelCount: 3,
    outChannelCount: 3,
    gridPointCount: new byte[] { 2, 2, 2 },
    IccClutDataType.Float32,
    values);

// Verify DataType before writing
if (clut.DataType is not (IccClutDataType.UInt8 or IccClutDataType.UInt16 or IccClutDataType.Float32))
    throw new ArgumentException("CLUT DataType must be UInt8, UInt16, or Float32");

try { writer.WriteClut(clut); }
catch (InvalidIccProfileException ex) when (ex.Message.Contains("CLUT data type"))
{
    // re-initialize clut with explicit, valid DataType
    clut = RecreateClutWithValidDataType(clut);
    writer.WriteClut(clut);
}

When it happens

Trigger: Calling WriteClut (via WriteClutProcessElement / WriteLutAtoBTagDataEntry / WriteLutBToATagDataEntry) with an IccClut whose DataType property is an undefined/invalid IccClutDataType value (e.g. default-initialized struct or manually cast value).

Common situations: Programmatic ICC profile generation with a partially initialized IccClut; deserializing a CLUT from an unsupported profile and re-serializing without fixing DataType; enum casts from ints out of range.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Invalid CLUT size of
• Invalid CLUT dimensions.
• The CLUT data is shorter than its declared dimensions.
• Invalid CurveSegment type of
• Invalid MultiProcessElement type of

AI-assisted analysis of SixLabors/ImageSharp@59ce6af6fc (2026-09-13). Data as JSON: /api/errors/7e28447fa5f54b4f. Report an issue: GitHub.

Appendix: source

Thrown at src/ImageSharp/Metadata/Profiles/ICC/DataWriter/IccDataWriter.Lut.cs:65

    {
        int count = this.WriteArray(value.GridPointCount);
        count += this.WriteEmpty(16 - value.GridPointCount.Length);

        switch (value.DataType)
        {
            case IccClutDataType.Float:
                return count + this.WriteClutF32(value);
            case IccClutDataType.UInt8:
                count += this.WriteByte(1);
                count += this.WriteEmpty(3);
                return count + this.WriteClut8(value);
            case IccClutDataType.UInt16:
                count += this.WriteByte(2);
                count += this.WriteEmpty(3);
                return count + this.WriteClut16(value);

            default:
                throw new InvalidIccProfileException($"Invalid CLUT data type of {value.DataType}");
        }
    }

    /// <summary>
    /// Writes a 8bit color lookup table.
    /// </summary>
    /// <param name="value">The CLUT to write.</param>
    /// <returns>The number of bytes written.</returns>
    public int WriteClut8(IccClut value)
    {
        int count = 0;
        foreach (float item in value.Values)
        {
            count += this.WriteByte((byte)Numerics.Clamp((item * byte.MaxValue) + 0.5F, 0, byte.MaxValue));
        }

        return count;
    }

View on GitHub (pinned to 59ce6af6fc)