dotnet/machinelearning · error · ArgumentException

Saving image with the format '{ext}' is not supported. Try s

Error message

Saving image with the format '{ext}' is not supported. Try save it with `Jpeg`, `Png`, or `Webp` format.

What it means

After selecting an encoding format from the extension, Save calls _image.Encode(encodingFormat, 100). If SkiaSharp's encoder returns null for that format, the format is effectively unsupported by the encoder and ArgumentException is thrown.

Source

Thrown at src/Microsoft.ML.ImageAnalytics/MLImage.cs:246

        /// <summary>
        /// Save the current image to a file.
        /// </summary>
        /// <param name="imagePath">The path of the file to save the image to.</param>
        /// <remarks>The saved image encoding will be detected from the file extension.</remarks>
        public void Save(string imagePath)
        {
            ThrowInvalidOperationExceptionIfDisposed();
            string ext = Path.GetExtension(imagePath);

            if (!_extensionToEncodingFormat.TryGetValue(ext, out SKEncodedImageFormat encodingFormat))
            {
                throw new ArgumentException($"Path has invalid image file extension.", nameof(imagePath));
            }

            using SKData data = _image.Encode(encodingFormat, 100);
            if (data is null)
            {
                throw new ArgumentException($"Saving image with the format '{ext}' is not supported. Try save it with `Jpeg`, `Png`, or `Webp` format.", nameof(imagePath));
            }

            using var stream = new FileStream(imagePath, FileMode.Create, FileAccess.Write);
            data.SaveTo(stream);
        }

        /// <summary>
        /// Disposes the image.
        /// </summary>
        public void Dispose()
        {
            if (_image != null)
            {
                _image.Dispose();
                _image = null;
            }
        }

View on GitHub (pinned to 7b76e69cf9)

Solutions

1. Save as Jpeg, Png, or Webp as the message suggests
2. Update the SkiaSharp native assets to a build that includes the needed encoder
3. Catch ArgumentException and retry with a .png path

Example fix

// before
image.Save("out.webp"); // encoder returned null
// after
try { image.Save("out.webp"); } catch (ArgumentException) { image.Save("out.png"); }

// no pre-call API surface; prefer known-good formats
string ext = Path.GetExtension(path).ToLowerInvariant();
bool knownGood = ext is ".jpg" or ".jpeg" or ".png" or ".webp";

try { image.Save(path); } catch (ArgumentException ex) when (ex.Message.Contains("is not supported")) { image.Save(Path.ChangeExtension(path, ".png")); }

When it happens

Trigger: Calling Save with a recognized extension whose SKImage encode operation returns null — typically when the SkiaSharp build lacks the encoder for that format.

Common situations: Rare encoder-availability differences across platforms/SkiaSharp versions; mostly avoided by sticking to JPEG, PNG, or WebP.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Invalid imagePixelData buffer size.
• Pixel data is unavailable.
• Path has invalid image file extension.
• Unsupported image format.
• Invalid resize mode value.

AI-assisted analysis of dotnet/machinelearning@7b76e69cf9 (2026-09-11). Data as JSON: /api/errors/0dc9104cd670d14c. Report an issue: GitHub.