Add bits per pixel in webp image info

src/ImageSharp/Formats/WebP/WebPBitsPerPixel.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.WebP
+{
+    /// <summary>
+    /// Enumerates the available bits per pixel the webp image uses.
+    /// </summary>
+    public enum WebPBitsPerPixel : short
+    {
+        /// <summary>
+        /// 24 bits per pixel. Each pixel consists of 3 bytes.
+        /// </summary>
+        Pixel24 = 24,
+
+        /// <summary>
+        /// 32 bits per pixel. Each pixel consists of 4 bytes (an alpha channel is present).
+        /// </summary>
+        Pixel32 = 32
+    }
+}

src/ImageSharp/Formats/WebP/WebPDecoderCore.cs

@@ -118,9 +118,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
             this.ReadImageHeader();
             WebPImageInfo imageInfo = this.ReadVp8Info();
 
-            // TODO: not sure yet where to get this info. Assuming 24 bits for now.
-            int bitsPerPixel = 24;
-            return new ImageInfo(new PixelTypeInfo(bitsPerPixel), imageInfo.Width, imageInfo.Height, this.Metadata);
+            return new ImageInfo(new PixelTypeInfo((int)imageInfo.BitsPerPixel), imageInfo.Width, imageInfo.Height, this.Metadata);
         }
 
         /// <summary>
@@ -341,9 +339,10 @@ namespace SixLabors.ImageSharp.Formats.WebP
                    {
                        Width = width,
                        Height = height,
+                       BitsPerPixel = features?.Alpha is true ? WebPBitsPerPixel.Pixel32 : WebPBitsPerPixel.Pixel24,
                        IsLossLess = false,
                        ImageDataSize = dataSize,
-                       Features = features
+                       Features = features,
                    };
         }
 
@@ -388,6 +387,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                    {
                        Width = (int)width,
                        Height = (int)height,
+                       BitsPerPixel = WebPBitsPerPixel.Pixel32,
                        IsLossLess = true,
                        ImageDataSize = imageDataSize,
                        Features = features,

src/ImageSharp/Formats/WebP/WebPImageInfo.cs

@@ -15,6 +15,11 @@ namespace SixLabors.ImageSharp.Formats.WebP
         /// </summary>
         public int Height { get; set; }
 
+        /// <summary>
+        /// Gets or sets the bits per pixel.
+        /// </summary>
+        public WebPBitsPerPixel BitsPerPixel { get; set; }
+
         /// <summary>
         /// Gets or sets a value indicating whether this image uses a lossless compression.
         /// </summary>