Preserve lossy/lossless encoding, if input image was webp

src/ImageSharp/Formats/Webp/IWebpEncoderOptions.cs

@@ -12,7 +12,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// Gets a value indicating whether lossy compression should be used.
         /// If false, lossless compression will be used.
         /// </summary>
-        bool Lossy { get; }
+        bool? Lossy { get; }
 
         /// <summary>
         /// Gets the compression quality. Between 0 and 100.

src/ImageSharp/Formats/Webp/WebpEncoder.cs

@@ -15,7 +15,7 @@ namespace SixLabors.ImageSharp.Formats.Webp
     public sealed class WebpEncoder : IImageEncoder, IWebpEncoderOptions
     {
         /// <inheritdoc/>
-        public bool Lossy { get; set; }
+        public bool? Lossy { get; set; }
 
         /// <inheritdoc/>
         public int Quality { get; set; } = 75;

src/ImageSharp/Formats/Webp/WebpEncoderCore.cs

@@ -4,9 +4,11 @@
 using System.IO;
 using System.Threading;
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.Formats.Webp.Lossless;
 using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 
 namespace SixLabors.ImageSharp.Formats.Webp
@@ -27,11 +29,6 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         private readonly bool alphaCompression;
 
-        /// <summary>
-        /// Indicating whether lossy compression should be used. If false, lossless compression will be used.
-        /// </summary>
-        private readonly bool lossy;
-
         /// <summary>
         /// Compression quality. Between 0 and 100.
         /// </summary>
@@ -73,6 +70,11 @@ namespace SixLabors.ImageSharp.Formats.Webp
         /// </summary>
         private readonly int nearLosslessQuality;
 
+        /// <summary>
+        /// Indicating whether lossy compression should be used. If false, lossless compression will be used.
+        /// </summary>
+        private bool? lossy;
+
         /// <summary>
         /// The global configuration.
         /// </summary>
@@ -112,8 +114,11 @@ namespace SixLabors.ImageSharp.Formats.Webp
             Guard.NotNull(stream, nameof(stream));
 
             this.configuration = image.GetConfiguration();
+            ImageMetadata metadata = image.Metadata;
+            WebpMetadata webpMetadata = metadata.GetWebpMetadata();
+            this.lossy ??= webpMetadata.Format == WebpFormatType.Lossy;
 
-            if (this.lossy)
+            if (this.lossy.GetValueOrDefault())
             {
                 using var enc = new Vp8Encoder(
                     this.memoryAllocator,

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

@@ -111,7 +111,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
             };
 
             // Convert image pixels to bgra array.
-            byte[] imgBytes = File.ReadAllBytes(TestImageFullPath(TestImages.Webp.Lossless.BikeSmall));
+            byte[] imgBytes = File.ReadAllBytes(TestImageFullPath(TestImages.Webp.Lossy.BikeSmall));
             using var image = Image.Load<Rgba32>(imgBytes, new WebpDecoder());
             uint[] bgra = ToBgra(image);
 

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

@@ -3,6 +3,7 @@
 
 using System.IO;
 using SixLabors.ImageSharp.Formats.Webp;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using Xunit;
@@ -14,6 +15,26 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
     [Trait("Format", "Webp")]
     public class WebpEncoderTests
     {
+        [Theory]
+        [WithFile(Flag, PixelTypes.Rgba32, WebpFormatType.Lossless)] // if its not a webp input image, it should default to lossless.
+        [WithFile(Lossless.NoTransform1, PixelTypes.Rgba32, WebpFormatType.Lossless)]
+        [WithFile(Lossy.Bike, PixelTypes.Rgba32, WebpFormatType.Lossy)]
+        public void Encode_PreserveRatio<TPixel>(TestImageProvider<TPixel> provider, WebpFormatType expectedFormat)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            var options = new WebpEncoder();
+            using Image<TPixel> input = provider.GetImage();
+            using var memoryStream = new MemoryStream();
+            input.Save(memoryStream, options);
+
+            memoryStream.Position = 0;
+            using var output = Image.Load<Rgba32>(memoryStream);
+
+            ImageMetadata meta = output.Metadata;
+            WebpMetadata webpMetaData = meta.GetWebpMetadata();
+            Assert.Equal(expectedFormat, webpMetaData.Format);
+        }
+
         [Theory]
         [WithFile(Flag, PixelTypes.Rgba32)]
         [WithFile(TestImages.Png.PalettedTwoColor, PixelTypes.Rgba32)]

tests/ImageSharp.Tests/TestImages.cs

@@ -603,8 +603,6 @@ namespace SixLabors.ImageSharp.Tests
                 // substract_green, predictor, cross_color
                 public const string BikeThreeTransforms = "Webp/bike_lossless.webp";
 
-                public const string BikeSmall = "Webp/bike_lossless_small.webp";
-
                 // Invalid / corrupted images
                 // Below images have errors according to webpinfo. The error message webpinfo gives is "Truncated data detected when parsing RIFF payload."
                 public const string LossLessCorruptImage1 = "Webp/lossless_big_random_alpha.webp"; // substract_green, predictor, cross_color.
@@ -621,6 +619,7 @@ namespace SixLabors.ImageSharp.Tests
                 public const string Earth = "Webp/earth_lossy.webp";
                 public const string WithExif = "Webp/exif_lossy.webp";
                 public const string WithIccp = "Webp/lossy_with_iccp.webp";
+                public const string BikeSmall = "Webp/bike_lossless_small.webp";
 
                 // Lossy images without macroblock filtering.
                 public const string Bike = "Webp/bike_lossy.webp";