dotnet/wpf · error · InvalidOperationException

SR.Image_PaletteZeroColors

Error message

SR.Image_PaletteZeroColors

What it means

BitmapPalette's constructor requires the colors collection to contain between 1 and 256 entries; an empty (or invalid-count) collection throws InvalidOperationException with SR.Image_PaletteZeroColors. A palette must map at least one color and at most 256 (8-bit index limit) colors.

Solutions

  1. Check colors.Count is between 1 and 256 before constructing the BitmapPalette.
  2. Provide a default palette (e.g. BitmapPalettes.WebPalette) when no colors were extracted.
  3. Skip palette creation entirely for non-paletted pixel formats (PalettColor formats only).

Example fix

// before
var palette = new BitmapPalette(collectedColors); // empty
// after
if (collectedColors.Count > 0)
    var palette = new BitmapPalette(collectedColors);
else
    var palette = BitmapPalettes.Gray256;
Defensive patterns

Strategy: validation

Validate before calling

if (colors == null || colors.Count < 1 || colors.Count > 256)
    throw new ArgumentOutOfRangeException(nameof(colors), "palette must have 1-256 colors");

Type guard

bool IsValidPalette(IList<Color> colors) => colors != null && colors.Count >= 1 && colors.Count <= 256;

Try / catch

try { var p = new BitmapPalette(colors); } catch (InvalidOperationException) { p = BitmapPalettes.WebPalette; }

Prevention

When it happens

Trigger: new BitmapPalette(new Color[0]) or passing an empty IList<Color>; also the internal UpdateManaged path when WIC reports 0 colors.

Common situations: Building a palette dynamically from image data that yielded no colors; decoding a malformed paletted image where the color table is empty; default-constructed color lists passed straight to the constructor.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/55c4fbc894f0ed1f. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapPalette.cs:37

        /// <summary>
        /// No public default constructor
        /// </summary>
        private BitmapPalette()
        {
        }

        /// <summary>
        /// Create a palette from the list of colors.
        /// </summary>
        public BitmapPalette(IList<Color> colors)
        {
            ArgumentNullException.ThrowIfNull(colors);

            int count = colors.Count;

            if (count < 1 || count > 256)
            {
                throw new InvalidOperationException(SR.Format(SR.Image_PaletteZeroColors, null));
            }

            Color[] colorArray = new Color[count];

            for (int i = 0; i < count; ++i)
            {
                colorArray[i] = colors[i];
            }

            _colors = new ReadOnlyCollection<Color>(colorArray);

            _palette = CreateInternalPalette();

            UpdateUnmanaged();
        }

        /// <summary>
        /// Construct BitmapPalette from a BitmapSource.

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