Add filter strength as encoder parameter

src/ImageSharp/Formats/WebP/IWebpEncoderOptions.cs

@@ -39,6 +39,15 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         int EntropyPasses { get; }
 
+        /// <summary>
+        /// Gets the strength of the deblocking filter, between 0 (no filtering) and 100 (maximum filtering).
+        /// A value of 0 will turn off any filtering. Higher value will increase the strength of the filtering process applied after decoding the picture.
+        /// The higher the value the smoother the picture will appear.
+        /// Typical values are usually in the range of 20 to 50.
+        /// Defaults to 60.
+        /// </summary>
+        int FilterStrength { get; }
+
         /// <summary>
         /// Gets a value indicating whether to preserve the exact RGB values under transparent area. Otherwise, discard this invisible
         /// RGB information for better compression.

src/ImageSharp/Formats/WebP/Lossy/Vp8Encoder.cs

@@ -42,6 +42,11 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
         /// </summary>
         private readonly int entropyPasses;
 
+        /// <summary>
+        /// Specify the strength of the deblocking filter, between 0 (no filtering) and 100 (maximum filtering). A value of 0 will turn off any filtering.
+        /// </summary>
+        private readonly int filterStrength;
+
         /// <summary>
         /// A bit writer for writing lossy webp streams.
         /// </summary>
@@ -78,11 +83,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
 
         private const int QMax = 100;
 
-        // TODO: filterStrength is hardcoded, should be configurable.
-        private const int FilterStrength = 60;
-
         /// <summary>
-        /// Initializes a new instance of the <see cref="Vp8Encoder"/> class.
+        /// Initializes a new instance of the <see cref="Vp8Encoder" /> class.
         /// </summary>
         /// <param name="memoryAllocator">The memory allocator.</param>
         /// <param name="configuration">The global configuration.</param>
@@ -91,7 +93,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
         /// <param name="quality">The encoding quality.</param>
         /// <param name="method">Quality/speed trade-off (0=fast, 6=slower-better).</param>
         /// <param name="entropyPasses">Number of entropy-analysis passes (in [1..10]).</param>
-        public Vp8Encoder(MemoryAllocator memoryAllocator, Configuration configuration, int width, int height, int quality, int method, int entropyPasses)
+        /// <param name="filterStrength">The filter the strength of the deblocking filter, between 0 (no filtering) and 100 (maximum filtering).</param>
+        public Vp8Encoder(MemoryAllocator memoryAllocator, Configuration configuration, int width, int height, int quality, int method, int entropyPasses, int filterStrength)
         {
             this.memoryAllocator = memoryAllocator;
             this.configuration = configuration;
@@ -100,6 +103,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             this.quality = Numerics.Clamp(quality, 0, 100);
             this.method = Numerics.Clamp(method, 0, 6);
             this.entropyPasses = Numerics.Clamp(entropyPasses, 1, 10);
+            this.filterStrength = Numerics.Clamp(filterStrength, 0, 100);
             this.rdOptLevel = (method >= 6) ? Vp8RdLevel.RdOptTrellisAll
                 : (method >= 5) ? Vp8RdLevel.RdOptTrellis
                 : (method >= 3) ? Vp8RdLevel.RdOptBasic
@@ -476,7 +480,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
 
         private void AdjustFilterStrength()
         {
-            if (FilterStrength > 0)
+            if (this.filterStrength > 0)
             {
                 int maxLevel = 0;
                 for (int s = 0; s < WebpConstants.NumMbSegments; s++)
@@ -708,7 +712,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossy
             int filterType = 1; // TODO: filterType is hardcoded
 
             // level0 is in [0..500]. Using '-f 50' as filter_strength is mid-filtering.
-            int level0 = 5 * FilterStrength;
+            int level0 = 5 * this.filterStrength;
             for (int i = 0; i < WebpConstants.NumMbSegments; ++i)
             {
                 Vp8SegmentInfo m = this.SegmentInfos[i];

src/ImageSharp/Formats/WebP/WebpEncoder.cs

@@ -29,6 +29,9 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// <inheritdoc/>
         public int EntropyPasses { get; set; }
 
+        /// <inheritdoc/>
+        public int FilterStrength { get; set; } = 60;
+
         /// <inheritdoc/>
         public bool Exact { get; set; }
 

src/ImageSharp/Formats/WebP/WebpEncoderCore.cs

@@ -47,6 +47,11 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         private readonly int entropyPasses;
 
+        /// <summary>
+        /// The filter the strength of the deblocking filter, between 0 (no filtering) and 100 (maximum filtering).
+        /// </summary>
+        private readonly int filterStrength;
+
         /// <summary>
         /// Flag indicating whether to preserve the exact RGB values under transparent area. Otherwise, discard this invisible
         /// RGB information for better compression.
@@ -71,6 +76,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
             this.quality = options.Quality;
             this.method = options.Method;
             this.entropyPasses = options.EntropyPasses;
+            this.filterStrength = options.FilterStrength;
             this.exact = options.Exact;
         }
 
@@ -91,7 +97,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
 
             if (this.lossy)
             {
-                using var enc = new Vp8Encoder(this.memoryAllocator, this.configuration, image.Width, image.Height, this.quality, this.method, this.entropyPasses);
+                using var enc = new Vp8Encoder(this.memoryAllocator, this.configuration, image.Width, image.Height, this.quality, this.method, this.entropyPasses, this.filterStrength);
                 enc.Encode(image, stream);
             }
             else

tests/ImageSharp.Tests/Formats/WebP/WebpEncoderTests.cs

@@ -98,6 +98,26 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
             image.VerifyEncoder(provider, "webp", testOutputDetails, encoder, customComparer: GetComparer(quality));
         }
 
+        [Theory]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 100)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 80)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 50)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 30)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 10)]
+        public void Encode_Lossy_WithDifferentFilterStrength_Works<TPixel>(TestImageProvider<TPixel> provider, int filterStrength)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            var encoder = new WebpEncoder()
+            {
+                Lossy = true,
+                FilterStrength = filterStrength
+            };
+
+            using Image<TPixel> image = provider.GetImage();
+            string testOutputDetails = string.Concat("lossy", "_f", filterStrength);
+            image.VerifyEncoder(provider, "webp", testOutputDetails, encoder, customComparer: GetComparer(75));
+        }
+
         [Theory]
         [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 0, 75)]
         [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 1, 75)]