What causes "SR.Effect_PixelFormat" in dotnet/wpf?

Pass an explicit concrete format matching the buffer, e.g. PixelFormats.Bgra32, Bgr32, Gray8, Pbgra32

dotnet/wpf · error · ArgumentException

SR.Effect_PixelFormat

Error message

SR.Effect_PixelFormat

What it means

PixelFormats.Default ('don't care' — let the system pick) is not a valid source format for CachedBitmap: when created from raw memory the format must be known exactly to interpret the buffer. Passing Default (GUID WICPixelFormatDontCare) throws an ArgumentException naming the offending format.

Solutions

Pass an explicit concrete format matching the buffer, e.g. PixelFormats.Bgra32, Bgr32, Gray8, Pbgra32
Ensure the format matches the element size and stride of the pixel array
Replace default-initialized PixelFormat fields with a real format before constructing

Example fix

// before
var bmp = new CachedBitmap(pixels, w, h, 96, 96, PixelFormats.Default, null, stride);
// after
var bmp = new CachedBitmap(pixels, w, h, 96, 96, PixelFormats.Bgra32, null, stride);

Defensive patterns

Strategy: validation

Validate before calling

if (format == PixelFormats.Default)
    format = PixelFormats.Bgra32; // pick a concrete format matching your buffer

Type guard

static bool IsConcrete(PixelFormat f) => f != PixelFormats.Default && f.Guid != Guid.Empty;

Try / catch

try { return new CachedBitmap(pixels, w, h, dpiX, dpiY, fmt, palette, stride); }
catch (ArgumentException ex) when (ex.ParamName == "pixelFormat") { return new CachedBitmap(pixels, w, h, dpiX, dpiY, PixelFormats.Bgra32, palette, stride); }

Prevention

Never use PixelFormats.Default with from-memory bitmap construction
Derive the format from the buffer's element size (1B=Gray8, 4B=Bgra32, etc.)
Initialize PixelFormat fields to a concrete default, not Default

When it happens

Trigger: new CachedBitmap(pixels, w, h, dpiX, dpiY, PixelFormats.Default, palette, stride) — explicitly passing the Default PixelFormat for a from-memory construction.

Common situations: Copying code from BitmapSource usage where Default is sometimes acceptable; a PixelFormat variable that was never initialized and defaulted to Default; generic image pipelines that defer format choice.

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/f5b9a12ae26f761a. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/CachedBitmap.cs:348

        ///
        private void InitFromMemoryPtr(
                    int pixelWidth,
                    int pixelHeight,
                    double dpiX,
                    double dpiY,
                    PixelFormat pixelFormat,
                    BitmapPalette palette,
                    IntPtr buffer,
                    int bufferSize,
                    int stride
                    )
        {
            if (pixelFormat.Palettized && palette == null)
                throw new InvalidOperationException(SR.Image_IndexedPixelFormatRequiresPalette);

            if (pixelFormat.Format == PixelFormatEnum.Default && pixelFormat.Guid == WICPixelFormatGUIDs.WICPixelFormatDontCare)
            {
                throw new System.ArgumentException(
                        SR.Format(SR.Effect_PixelFormat, pixelFormat),
                        nameof(pixelFormat)
                        );
            }

            _bitmapInit.BeginInit();

            try
            {
                BitmapSourceSafeMILHandle wicBitmap;

                // Create the unmanaged resources
                Guid guidFmt = pixelFormat.Guid;

                using (FactoryMaker factoryMaker = new FactoryMaker())
                {
                    HRESULT.Check(UnsafeNativeMethods.WICImagingFactory.CreateBitmapFromMemory(
                            factoryMaker.ImagingFactoryPtr,

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