dotnet/wpf · error · InvalidOperationException

SR.Image_NoArgument

Error message

SR.Image_NoArgument

What it means

Like the other derived bitmaps, FormatConvertedBitmap requires a Source to convert. If EndInit runs while Source is null, IsValidForFinalizeCreation throws an InvalidOperationException (Image_NoArgument with "Source") — a format conversion cannot be finalized without an input image.

Solutions

1. Assign a valid BitmapSource to Source before calling EndInit
2. When using the convenience constructor new FormatConvertedBitmap(source, format, palette, alphaThreshold), Source is set automatically — prefer it
3. Create the FormatConvertedBitmap after the source BitmapImage has completed loading (e.g. in DownloadCompleted handler)

Example fix

// before
var fcb = new FormatConvertedBitmap();
fcb.BeginInit();
fcb.DestinationFormat = PixelFormats.Gray8;
fcb.EndInit(); // throws
// after
var fcb = new FormatConvertedBitmap();
fcb.BeginInit();
fcb.Source = new BitmapImage(new Uri("photo.png"));
fcb.DestinationFormat = PixelFormats.Gray8;
fcb.EndInit();

if (fcb.Source == null) throw new ArgumentException("Source required before EndInit", nameof(source));

static bool ReadyToConvert(FormatConvertedBitmap f) => f.Source != null && f.DestinationFormat != PixelFormats.Default;

try { fcb.EndInit(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("Source")) { fcb.Source = placeholderBitmap; fcb.EndInit(); }

When it happens

Trigger: new FormatConvertedBitmap { DestinationFormat = ... } with BeginInit/EndInit but no Source; XAML missing Source; Source bound to a value not yet loaded.

Common situations: Async image loading where binding has not delivered the BitmapImage before EndInit; code-built deferred init missing the Source assignment; refactors dropping the Source line.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Image_NeitherArgument (UriSource, StreamSource)
• SR.Image_NoArgument
• SR.Image_NoArgument
• Cannot initialize compressor.
• Image_EncoderNoColorContext

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/3db3cec881a2f5e5. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/FormatConvertedBitmap.cs:169

        /// </summary>
        private void SourcePropertyChangedHook(DependencyPropertyChangedEventArgs e)
        {
            if (!e.IsASubPropertyChange)
            {
                BitmapSource newSource = e.NewValue as BitmapSource;
                _source = newSource;
                RegisterDownloadEventSource(_source);
                _syncObject = (newSource != null) ? newSource.SyncObject : _bitmapInit;
            }
        }

        internal override bool IsValidForFinalizeCreation(bool throwIfInvalid)
        {
            if (Source == null)
            {
                if (throwIfInvalid)
                {
                    throw new InvalidOperationException(SR.Format(SR.Image_NoArgument, "Source"));
                }
                return false;
            }
            if (DestinationFormat.Palettized)
            {
                if (DestinationPalette == null)
                {
                    if (throwIfInvalid)
                    {
                        throw new InvalidOperationException(SR.Image_IndexedPixelFormatRequiresPalette);
                    }
                    return false;
                }
                else if ((1 << DestinationFormat.BitsPerPixel) < DestinationPalette.Colors.Count)
                {
                    if (throwIfInvalid)
                    {
                        throw new InvalidOperationException(SR.Image_PaletteColorsDoNotMatchFormat);

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