Basic metadata-only image parsing API

src/ImageSharp/Formats/Gif/GifDecoderCore.cs

@@ -180,17 +180,6 @@ public IImage Identify(Stream stream)
                 {
                     if (nextFlag == GifConstants.ImageLabel)
                     {
-                        GifImageDescriptor imageDescriptor = this.ReadImageDescriptor();
-
-                        // Determine the color table for this frame. If there is a local one, use it otherwise use the global color table.
-                        if (imageDescriptor.LocalColorTableFlag)
-                        {
-                            int length = imageDescriptor.LocalColorTableSize * 3;
-
-                            // Skip local color table block
-                            this.Skip(length);
-                        }
-
                         // Skip image block
                         this.Skip(0);
                     }

tests/ImageSharp.Tests/Formats/GeneralFormatTests.cs

@@ -3,11 +3,19 @@
 
 using System.IO;
 using SixLabors.ImageSharp.Formats;
+using SixLabors.ImageSharp.Formats.Bmp;
+using SixLabors.ImageSharp.Formats.Gif;
+using SixLabors.ImageSharp.Formats.Jpeg;
+using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.PixelFormats;
 using Xunit;
 
 namespace SixLabors.ImageSharp.Tests
 {
+    using System;
+
+
+
     public class GeneralFormatTests : FileTestBase
     {
         [Theory]
@@ -146,5 +154,56 @@ public void ImageShouldPreservePixelByteOrderWhenSerialized()
                 }
             }
         }
+
+        [Theory]
+        [InlineData(10, 10, "png")]
+        [InlineData(100, 100, "png")]
+        [InlineData(100, 10, "png")]
+        [InlineData(10, 100, "png")]
+        [InlineData(10, 10, "gif")]
+        [InlineData(100, 100, "gif")]
+        [InlineData(100, 10, "gif")]
+        [InlineData(10, 100, "gif")]
+        [InlineData(10, 10, "bmp")]
+        [InlineData(100, 100, "bmp")]
+        [InlineData(100, 10, "bmp")]
+        [InlineData(10, 100, "bmp")]
+        [InlineData(10, 10, "jpg")]
+        [InlineData(100, 100, "jpg")]
+        [InlineData(100, 10, "jpg")]
+        [InlineData(10, 100, "jpg")]
+        public void CanIdentifyImageLoadedFromBytes(int width, int height, string format)
+        {
+            using (Image<Rgba32> image = Image.LoadPixelData(new Rgba32[width * height], width, height))
+            {
+                using (var memoryStream = new MemoryStream())
+                {
+                    image.Save(memoryStream, GetEncoder(format));
+                    memoryStream.Position = 0;
+
+                    var imageInfo = Image.Identify(memoryStream);
+
+                    Assert.Equal(imageInfo.Width, width);
+                    Assert.Equal(imageInfo.Height, height);
+                }
+            }
+        }
+
+        private static IImageEncoder GetEncoder(string format)
+        {
+            switch (format)
+            {
+                case "png":
+                    return new PngEncoder();
+                case "gif":
+                    return new GifEncoder();
+                case "bmp":
+                    return new BmpEncoder();
+                case "jpg":
+                    return new JpegEncoder();
+                default:
+                    throw new ArgumentOutOfRangeException(nameof(format), format, null);
+            }
+        }
     }
 }

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -17,6 +17,7 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="CoreCompat.System.Drawing" Version="1.0.0-beta006" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
     <PackageReference Include="xunit" Version="2.3.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.0" />
     <PackageReference Include="Moq" Version="4.7.137" />