Use TransparentColorMode enum

src/ImageSharp/Formats/Webp/IWebpEncoderOptions.cs

@@ -59,9 +59,9 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// <summary>
         /// Gets a value indicating whether to preserve the exact RGB values under transparent area. Otherwise, discard this invisible
         /// RGB information for better compression.
-        /// The default value is false.
+        /// The default value is Clear.
         /// </summary>
-        bool Exact { get; }
+        WebpTransparentColorMode TransparentColorMode { get; }
 
         /// <summary>
         /// Gets a value indicating whether near lossless mode should be used.

src/ImageSharp/Formats/Webp/Lossless/PredictorEncoder.cs

@@ -43,7 +43,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             Span<uint> image,
             bool nearLossless,
             int nearLosslessQuality,
-            bool exact,
+            WebpTransparentColorMode transparentColorMode,
             bool usedSubtractGreen,
             bool lowEffort)
         {
@@ -81,7 +81,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                             bgraScratch,
                             bgra,
                             maxQuantization,
-                            exact,
+                            transparentColorMode,
                             usedSubtractGreen,
                             nearLossless,
                             image);
@@ -99,7 +99,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                 bgraScratch,
                 bgra,
                 maxQuantization,
-                exact,
+                transparentColorMode,
                 usedSubtractGreen,
                 nearLossless,
                 lowEffort);
@@ -189,7 +189,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             Span<uint> argbScratch,
             Span<uint> argb,
             int maxQuantization,
-            bool exact,
+            WebpTransparentColorMode transparentColorMode,
             bool usedSubtractGreen,
             bool nearLossless,
             Span<uint> modes)
@@ -272,7 +272,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                         }
                     }
 
-                    GetResidual(width, height, upperRow, currentRow, maxDiffs, mode, startX, startX + maxX, y, maxQuantization, exact, usedSubtractGreen, nearLossless, residuals);
+                    GetResidual(width, height, upperRow, currentRow, maxDiffs, mode, startX, startX + maxX, y, maxQuantization, transparentColorMode, usedSubtractGreen, nearLossless, residuals);
                     for (int relativeX = 0; relativeX < maxX; ++relativeX)
                     {
                         UpdateHisto(histoArgb, residuals[relativeX]);
@@ -330,12 +330,12 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             int xEnd,
             int y,
             int maxQuantization,
-            bool exact,
+            WebpTransparentColorMode transparentColorMode,
             bool usedSubtractGreen,
             bool nearLossless,
             Span<uint> output)
         {
-            if (exact)
+            if (transparentColorMode == WebpTransparentColorMode.Preserve)
             {
                 PredictBatch(mode, xStart, y, xEnd - xStart, currentRowSpan, upperRowSpan, output);
             }
@@ -568,7 +568,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             Span<uint> argbScratch,
             Span<uint> argb,
             int maxQuantization,
-            bool exact,
+            WebpTransparentColorMode transparentColorMode,
             bool usedSubtractGreen,
             bool nearLossless,
             bool lowEffort)
@@ -631,7 +631,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                             xEnd,
                             y,
                             maxQuantization,
-                            exact,
+                            transparentColorMode,
                             usedSubtractGreen,
                             nearLossless,
                             argb.Slice((y * width) + x));

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -58,7 +58,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// Flag indicating whether to preserve the exact RGB values under transparent area. Otherwise, discard this invisible
         /// RGB information for better compression.
         /// </summary>
-        private readonly bool exact;
+        private readonly WebpTransparentColorMode transparentColorMode;
 
         /// <summary>
         /// Indicating whether near lossless mode should be used.
@@ -85,7 +85,8 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
         /// <param name="height">The height of the input image.</param>
         /// <param name="quality">The encoding quality.</param>
         /// <param name="method">Quality/speed trade-off (0=fast, 6=slower-better).</param>
-        /// <param name="exact">Flag indicating whether to preserve the exact RGB values under transparent area. Otherwise, discard this invisible RGB information for better compression.</param>
+        /// <param name="transparentColorMode">Flag indicating whether to preserve the exact RGB values under transparent area.
+        /// Otherwise, discard this invisible RGB information for better compression.</param>
         /// <param name="nearLossless">Indicating whether near lossless mode should be used.</param>
         /// <param name="nearLosslessQuality">The near lossless quality. The range is 0 (maximum preprocessing) to 100 (no preprocessing, the default).</param>
         public Vp8LEncoder(
@@ -95,7 +96,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             int height,
             int quality,
             WebpEncodingMethod method,
-            bool exact,
+            WebpTransparentColorMode transparentColorMode,
             bool nearLossless,
             int nearLosslessQuality)
         {
@@ -106,7 +107,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
             this.configuration = configuration;
             this.quality = Numerics.Clamp(quality, 0, 100);
             this.method = method;
-            this.exact = exact;
+            this.transparentColorMode = transparentColorMode;
             this.nearLossless = nearLossless;
             this.nearLosslessQuality = Numerics.Clamp(nearLosslessQuality, 0, 100);
             this.bitWriter = new Vp8LBitWriter(initialSize);
@@ -676,7 +677,7 @@ namespace SixLabors.ImageSharp.Formats.Webp.Lossless
                 this.TransformData.GetSpan(),
                 this.nearLossless,
                 nearLosslessStrength,
-                this.exact,
+                this.transparentColorMode,
                 this.UseSubtractGreenTransform,
                 lowEffort);
 

src/ImageSharp/Formats/Webp/WebpEncoder.cs

@@ -36,7 +36,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         public int FilterStrength { get; set; } = 60;
 
         /// <inheritdoc/>
-        public bool Exact { get; set; }
+        public WebpTransparentColorMode TransparentColorMode { get; set; } = WebpTransparentColorMode.Clear;
 
         /// <inheritdoc/>
         public bool NearLossless { get; set; }

src/ImageSharp/Formats/Webp/WebpEncoderCore.cs

@@ -61,7 +61,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// Flag indicating whether to preserve the exact RGB values under transparent area. Otherwise, discard this invisible
         /// RGB information for better compression.
         /// </summary>
-        private readonly bool exact;
+        private readonly WebpTransparentColorMode transparentColorMode;
 
         /// <summary>
         /// Indicating whether near lossless mode should be used.
@@ -93,7 +93,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
             this.entropyPasses = options.EntropyPasses;
             this.spatialNoiseShaping = options.SpatialNoiseShaping;
             this.filterStrength = options.FilterStrength;
-            this.exact = options.Exact;
+            this.transparentColorMode = options.TransparentColorMode;
             this.nearLossless = options.NearLossless;
             this.nearLosslessQuality = options.NearLosslessQuality;
         }
@@ -136,7 +136,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
                     image.Height,
                     this.quality,
                     this.method,
-                    this.exact,
+                    this.transparentColorMode,
                     this.nearLossless,
                     this.nearLosslessQuality);
                 enc.Encode(image, stream);

src/ImageSharp/Formats/Webp/WebpTransparentColorMode.cs

@@ -0,0 +1,21 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+namespace SixLabors.ImageSharp.Formats.Webp
+{
+    /// <summary>
+    /// Enum indicating how the transparency should be handled on encoding.
+    /// </summary>
+    public enum WebpTransparentColorMode
+    {
+        /// <summary>
+        /// Discard the transparency information for better compression.
+        /// </summary>
+        Clear = 0,
+
+        /// <summary>
+        /// The transparency will be kept as is.
+        /// </summary>
+        Preserve = 1,
+    }
+}

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

@@ -111,14 +111,14 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
         [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 5)]
         [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 6)]
         [WithFile(Lossy.Alpha1, PixelTypes.Rgba32, 4)]
-        public void Encode_Lossless_WithExactFlag_Works<TPixel>(TestImageProvider<TPixel> provider, WebpEncodingMethod method)
+        public void Encode_Lossless_WithPreserveTransparentColor_Works<TPixel>(TestImageProvider<TPixel> provider, WebpEncodingMethod method)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             var encoder = new WebpEncoder()
             {
                 Lossy = false,
                 Method = method,
-                Exact = true
+                TransparentColorMode = WebpTransparentColorMode.Preserve
             };
 
             using Image<TPixel> image = provider.GetImage();