dotnet/machinelearning · error · ArgumentException

Invalid imagePixelData buffer size.

Error message

Invalid imagePixelData buffer size.

What it means

MLImage.CreateFromPixels validates that the imagePixelData buffer length exactly equals width*height*4 (4 bytes per pixel: BGRA32/RGBA32). If the supplied byte array does not match the declared dimensions, ArgumentException is thrown to prevent reading out-of-bounds or producing a corrupt SKBitmap.

Source

Thrown at src/Microsoft.ML.ImageAnalytics/MLImage.cs:100

        {
            if (pixelFormat != MLPixelFormat.Bgra32 && pixelFormat != MLPixelFormat.Rgba32)
            {
                throw new ArgumentException($"Unsupported pixel format", nameof(pixelFormat));
            }

            if (width <= 0)
            {
                throw new ArgumentException($"Invalid width value.", nameof(width));
            }

            if (height <= 0)
            {
                throw new ArgumentException($"Invalid height value.", nameof(height));
            }

            if (imagePixelData.Length != width * height * 4)
            {
                throw new ArgumentException($"Invalid {nameof(imagePixelData)} buffer size.");
            }

            SKBitmap image = new SKBitmap(new SKImageInfo(width, height, pixelFormat == MLPixelFormat.Bgra32 ? SKColorType.Bgra8888 : SKColorType.Rgba8888));

            Debug.Assert(image.Info.BitsPerPixel == 32);
            Debug.Assert(image.RowBytes * image.Height == width * height * 4);

            imagePixelData.CopyTo(new Span<byte>(image.GetPixels().ToPointer(), image.Width * image.Height * 4));

            return new MLImage(image);
        }

        /// <summary>
        /// Gets the pixel format for this Image.
        /// </summary>
        public MLPixelFormat PixelFormat
        {
            get

View on GitHub (pinned to 7b76e69cf9)

Solutions

1. Compute the expected size as width*height*4 and verify your buffer length before calling
2. Convert 3-byte-per-pixel data to 4-byte BGRA/RGBA before calling
3. If your source has row stride padding, copy row-by-row into a tightly packed buffer

Example fix

// before
MLImage.CreateFromPixels(width, height, rgbBytes); // rgbBytes.Length = w*h*3
// after
var bgra = new byte[width * height * 4];
for (int i = 0, j = 0; i < rgbBytes.Length; i += 3, j += 4) { bgra[j] = rgbBytes[i]; bgra[j+1] = rgbBytes[i+1]; bgra[j+2] = rgbBytes[i+2]; bgra[j+3] = 255; }
MLImage.CreateFromPixels(width, height, bgra);

if (pixels == null || pixels.Length != width * height * 4)
    throw new ArgumentException($"pixel buffer must be width*height*4 = {width * height * 4} bytes");

bool IsValidPixelBuffer(byte[] b, int w, int h) => b != null && b.Length == w * h * 4;

try { var img = MLImage.CreateFromPixels(w, h, buf); } catch (ArgumentException ex) when (ex.Message.Contains("buffer size")) { /* repack buffer to BGRA32 */ }

When it happens

Trigger: Calling MLImage.CreateFromPixels with a byte[] whose Length != width*height*4 — e.g. passing a buffer sized for 3 bytes per pixel (RGB), a stride-padded buffer, or dimensions that don't match the data.

Common situations: Converting from codecs that output RGB24 instead of RGBA32, forgetting that the buffer includes no row padding, or mixing up width/height order so the product is wrong.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Either input_ids or inputs_embeds must be set
• Dimension must be divisible by 2
• Directory "{0}" does not exist.
• Unsupported pixel format
• Invalid width value.

AI-assisted analysis of dotnet/machinelearning@7b76e69cf9 (2026-09-11). Data as JSON: /api/errors/247e8a01551650fa. Report an issue: GitHub.