specific PaletteSize property since ImageSharp does not provide the palette entries (SixLabors/ImageSharp#2404)

Author: IS4Code

SFI.Formats/Images/ImageAnalyzer.cs

@@ -1,13 +1,11 @@
-using IS4.SFI.MediaAnalysis.Images;
-using IS4.SFI.Services;
+using IS4.SFI.Services;
 using IS4.SFI.Tags;
 using IS4.SFI.Tools;
 using IS4.SFI.Vocabulary;
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Drawing;
-using System.Drawing.Imaging;
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
@@ -26,7 +24,7 @@ public class ImageAnalyzer : MediaObjectAnalyzer<IImage>
         /// </summary>
         [ComponentCollection("image-hash")]
         [Description("A collection of image-based hash algorithms that produce hashes from the low-detail form of the image.")]
-        public ICollection<IObjectHashAlgorithm<IImage>> LowFrequencyImageHashAlgorithms { get; } = new List<IObjectHashAlgorithm<Image>>();
+        public ICollection<IObjectHashAlgorithm<IImage>> LowFrequencyImageHashAlgorithms { get; } = new List<IObjectHashAlgorithm<IImage>>();
 
         /// <summary>
         /// A collection of byte-based hash algorithms producing hashes
@@ -97,10 +95,10 @@ public async override ValueTask<AnalysisResult> Analyze(IImage image, AnalysisCo
                 node.Set(Properties.Height, image.Height);
                 node.Set(Properties.HorizontalResolution, (decimal)image.HorizontalResolution);
                 node.Set(Properties.VerticalResolution, (decimal)image.VerticalResolution);
-                int paletteSize = image.Palette.Count;
+                var paletteSize = image.PaletteSize;
                 int bpp = image.BitDepth;
-                if(bpp != 0) node.Set(paletteSize > 0 ? Properties.BitDepth : Properties.ColorDepth, bpp);
-                if(paletteSize > 0) node.Set(Properties.PaletteSize, paletteSize);
+                if(bpp != 0) node.Set(paletteSize == 0 ? Properties.ColorDepth : Properties.BitDepth, bpp);
+                if(paletteSize is int size && size > 0) node.Set(Properties.PaletteSize, size);
             }
 
             if(!storedAsData)

SFI.Formats/Images/SharpImage.cs

@@ -4,6 +4,7 @@
 using SixLabors.ImageSharp;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Formats;
+using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing;
@@ -62,7 +63,25 @@ private double ResolutionUnit{
 
         public override int BitDepth => PixelType.BitsPerPixel;
 
-        public override IReadOnlyList<Color> Palette => Array.Empty<Color>(); // TODO
+        public override IReadOnlyList<Color> Palette => Array.Empty<Color>();
+
+        public override int? PaletteSize{
+            get{
+                if(Metadata.GetPngMetadata() is { } png)
+                {
+                    return png.ColorType == PngColorType.Palette ? null : 0;
+                }
+                if(Metadata.GetGifMetadata() is { } gif)
+                {
+                    return gif.GlobalColorTableLength;
+                }
+                if(Metadata.GetJpegMetadata() != null)
+                {
+                    return 0;
+                }
+                return null;
+            }
+        }
 
         [DynamicDependency(nameof(GetImagePixel), typeof(SharpImage))]
         public override Color GetPixel(int x, int y)

SFI/Services/IImage.cs

@@ -44,6 +44,11 @@ public interface IImage : IIdentityKey, IDisposable
         /// </summary>
         IReadOnlyList<Color> Palette { get; }
 
+        /// <summary>
+        /// The size of the color palette of the image.
+        /// </summary>
+        int? PaletteSize { get; }
+
         /// <summary>
         /// The format of the image.
         /// </summary>
@@ -234,6 +239,9 @@ protected ImageBase(TUnderlying underlyingImage, IFileFormat<TUnderlying> format
         /// <inheritdoc/>
         public abstract IReadOnlyList<Color> Palette { get; }
 
+        /// <inheritdoc/>
+        public virtual int? PaletteSize => Palette.Count;
+
         /// <inheritdoc/>
         public abstract int BitDepth { get; }