What causes "Bad configuration parameters" in d2phap/ImageGlass?

Inspect which advanced overload you called and whether its forced fields are compatible with your libwebp version.

d2phap/ImageGlass · error · Exception

Bad configuration parameters

Error message

Bad configuration parameters

What it means

Thrown by AdvancedEncode (the shared advanced encoder used by EncodeLossy/EncodeLossless/EncodeNearLossless advanced overloads) when LibWebp.WebPValidateConfig(ref config) != 1. WebPValidateConfig checks that the WebPConfig fields are internally consistent; a non-1 result means the assembled configuration is illegal (e.g. conflicting fields, out-of-range method/pass, or an incompatible lossless/lossy combination).

Source

Thrown at v9/Components/ImageGlass.WebP/WebPWrapper.cs:873

    /// <param name="config">Configuration for encode</param>
    /// <param name="info">True if need encode info.</param>
    /// <returns>Compressed data</returns>
    private byte[] AdvancedEncode(Bitmap bmp, WebPConfig config, bool info)
    {
        byte[]? rawWebP = null;
        byte[]? dataWebp = null;
        var wpic = new WebPPicture();
        BitmapData? bmpData = null;
        var stats = new WebPAuxStats();
        var ptrStats = IntPtr.Zero;
        var pinnedArrayHandle = new GCHandle();
        int dataWebpSize;

        try
        {
            // Validate the configuration
            if (LibWebp.WebPValidateConfig(ref config) != 1)
                throw new Exception("Bad configuration parameters");

            // test bmp
            if (bmp.Width == 0 || bmp.Height == 0)
                throw new ArgumentException("Bitmap contains no data.", nameof(bmp));
            if (bmp.Width > WEBP_MAX_DIMENSION || bmp.Height > WEBP_MAX_DIMENSION)
                throw new NotSupportedException($"Bitmap's dimension is too large. Max is {WEBP_MAX_DIMENSION}x{WEBP_MAX_DIMENSION} pixels.");
            if (bmp.PixelFormat != PixelFormat.Format24bppRgb && bmp.PixelFormat != PixelFormat.Format32bppArgb)
                throw new NotSupportedException("Only support Format24bppRgb and Format32bppArgb pixelFormat.");

            // Setup the input data, allocating a the bitmap, width and height
            bmpData = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, bmp.PixelFormat);
            if (LibWebp.WebPPictureInitInternal(ref wpic) != 1)
                throw new Exception("Can't initialize WebPPictureInit");
            wpic.width = (int)bmp.Width;
            wpic.height = (int)bmp.Height;
            wpic.use_argb = 1;

            if (bmp.PixelFormat == PixelFormat.Format32bppArgb)

View on GitHub (pinned to 4a3c4fecef)

Solutions

Inspect which advanced overload you called and whether its forced fields are compatible with your libwebp version.
Update libwebp to a version that accepts the wrapper's full config (partitions=3, segments=4, preprocessing=4 require newer builds).
Use the simple APIs (EncodeLossy(bmp, quality) / EncodeLossless(bmp)) that bypass WebPValidateConfig.
Reproduce the config and call WebPValidateConfig yourself to isolate the offending field.

Example fix

// before
var bytes = webp.EncodeLossy(bmp, quality, speed, info: true); // advanced, may produce bad config

// after
var bytes = webp.EncodeLossy(bmp, quality); // simple API, no WebPValidateConfig risk

Defensive patterns

Strategy: try-catch

Validate before calling

// Advanced config is built internally; pre-validate by preferring the simple API
// unless you need advanced tuning. Clamp speed/quality before calling.
int s = Math.Clamp(speed, 0, 9); int q = Math.Clamp(quality, 0, 100);

Try / catch

try { var bytes = webp.EncodeLossy(bmp, quality, speed); }
catch (Exception ex) when (ex.Message == "Bad configuration parameters")
{ var bytes = webp.EncodeLossy(bmp, quality); /* simple API */ }

Prevention

Use the simple APIs unless you need advanced tuning.
Update libwebp to accept the wrapper's full config set.
Reproduce the failing config and call WebPValidateConfig to isolate the offending field.

When it happens

Trigger: Reaching AdvancedEncode with a config whose field combination fails WebPValidateConfig — bad method value, partitions/segments out of range, lossless flag mixed with lossy-only options, or near_lossless set without lossless=1.

Common situations: The advanced overloads in this wrapper set many config fields (method, segments, partitions, alpha_filtering, near_lossless, exact) directly; any combination libwebp rejects produces this error before the bitmap is even inspected.

Related errors

AI-assisted analysis of d2phap/ImageGlass@4a3c4fecef (2026-08-13). Data as JSON: /api/errors/0f8a4a0b7e875f03. Report an issue: GitHub.