What causes "This DLL version not support EncodeNearLossless" in d2phap/ImageGlass?

Update the bundled libwebp to a recent build (>= 0.1.0.4 / 1083+) that supports near-lossless encoding.

d2phap/ImageGlass · error · Exception

This DLL version not support EncodeNearLossless

Error message

This DLL version not support EncodeNearLossless

What it means

Thrown by EncodeNearLossless when LibWebp.WebPGetDecoderVersion() returns <= 1082. Near-lossless encoding was added to libwebp after version 0.1.0.3 (1082), so older binaries simply do not expose the required functions. The wrapper refuses to proceed rather than calling a missing P/Invoke.

Source

Thrown at v9/Components/ImageGlass.WebP/WebPWrapper.cs:574

        config.pass = speed + 1;
        config.thread_level = 1;
        config.alpha_filtering = 2;
        config.use_sharp_yuv = 1;
        config.exact = 0;

        return AdvancedEncode(bmp, config, false);
    }

    /// <summary>Near lossless encoding image in bitmap</summary>
    /// <param name="bmp">Bitmap with the image</param>
    /// <param name="quality">Between 0 (lower quality, lowest file size) and 100 (highest quality, higher file size)</param>
    /// <param name="speed">Between 0 (fastest, lowest compression) and 9 (slower, best compression)</param>
    /// <returns>Compress data</returns>
    public byte[] EncodeNearLossless(Bitmap bmp, int quality, int speed = 9)
    {
        //test DLL version
        if (LibWebp.WebPGetDecoderVersion() <= 1082)
            throw new Exception("This DLL version not support EncodeNearLossless");

        //Inicialize config struct
        WebPConfig config = new WebPConfig();

        //Set compression parameters
        if (LibWebp.WebPConfigInit(ref config, WebPPreset.WEBP_PRESET_DEFAULT, (speed + 1) * 10) == 0)
            throw new Exception("Can't configure preset");
        if (LibWebp.WebPConfigLosslessPreset(ref config, speed) == 0)
            throw new Exception("Can't configure lossless preset");
        config.pass = speed + 1;
        config.near_lossless = quality;
        config.thread_level = 1;
        config.alpha_filtering = 2;
        config.use_sharp_yuv = 1;
        config.exact = 0;

        return AdvancedEncode(bmp, config, false);
    }

View on GitHub (pinned to 4a3c4fecef)

Solutions

Update the bundled libwebp to a recent build (>= 0.1.0.4 / 1083+) that supports near-lossless encoding.
Check WebPWrapper.GetVersion() at startup and disable the near-lossless code path if the version is too old.
Fall back to EncodeLossless(bmp, speed) when near-lossless is unavailable.

Example fix

// before
var bytes = webp.EncodeNearLossless(bmp, quality, speed);

// after
if (LibWebp.WebPGetDecoderVersion() <= 1082)
    bytes = webp.EncodeLossless(bmp, speed);
else
    bytes = webp.EncodeNearLossless(bmp, quality, speed);

Defensive patterns

Strategy: type-guard

Validate before calling

bool supportsNearLossless = LibWebp.WebPGetDecoderVersion() > 1082;
var bytes = supportsNearLossless
    ? webp.EncodeNearLossless(bmp, quality, speed)
    : webp.EncodeLossless(bmp, speed);

Type guard

static bool SupportsNearLossless() => LibWebp.WebPGetDecoderVersion() > 1082;

Try / catch

try { var bytes = webp.EncodeNearLossless(bmp, quality, speed); }
catch (Exception ex) when (ex.Message.Contains("not support EncodeNearLossless"))
{ var bytes = webp.EncodeLossless(bmp, speed); }

Prevention

Gating on DLL version at startup avoids the runtime exception entirely.
Keep libwebp current to access newer encode modes.
Provide a documented fallback when the host's libwebp is too old.

When it happens

Trigger: Calling EncodeNearLossless(bmp, quality, speed) while the loaded libwebp reports a version number <= 1082 (older libwebp).

Common situations: Shipping an old libwebp.dll; a system where an outdated libwebp is on the path; a third-party app embedding a legacy build.

Related errors

AI-assisted analysis of d2phap/ImageGlass@4a3c4fecef (2026-08-13). Data as JSON: /api/errors/f29d7a8c8e3b30b3. Report an issue: GitHub.