Clamp JPEG quality estimation results.

src/ImageSharp/Formats/Jpeg/Components/Quantization.cs

@@ -146,7 +146,7 @@ internal static class Quantization
             quality = (int)Math.Round(5000.0 / sumPercent);
         }
 
-        return quality;
+        return Numerics.Clamp(quality, MinQualityFactor, MaxQualityFactor);
     }
 
     /// <summary>

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.Metadata.cs

@@ -8,6 +8,7 @@ using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Processing;
 using SixLabors.ImageSharp.Tests.TestUtilities;
 
 // ReSharper disable InconsistentNaming
@@ -425,6 +426,32 @@ public partial class JpegDecoderTests
         VerifyEncodedStrings(exif);
     }
 
+    // https://github.com/SixLabors/ImageSharp/issues/2758
+    [Theory]
+    [WithFile(TestImages.Jpeg.Issues.Issue2758, PixelTypes.L8)]
+    public void Issue2758_DecodeWorks<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(JpegDecoder.Instance);
+
+        Assert.Equal(59787, image.Width);
+        Assert.Equal(511, image.Height);
+
+        JpegMetadata meta = image.Metadata.GetJpegMetadata();
+
+        // Quality determination should be between 1-100.
+        Assert.Equal(15, meta.LuminanceQuality);
+        Assert.Equal(1, meta.ChrominanceQuality);
+
+        // We want to test the encoder to ensure the determined values can be encoded but not by encoding
+        // the full size image as it would be too slow.
+        // We will crop the image to a smaller size and then encode it.
+        image.Mutate(x => x.Crop(new(0, 0, 100, 100)));
+
+        using MemoryStream ms = new();
+        image.Save(ms, new JpegEncoder());
+    }
+
     private static void VerifyEncodedStrings(ExifProfile exif)
     {
         Assert.NotNull(exif);

tests/ImageSharp.Tests/TestImages.cs

@@ -320,6 +320,7 @@ public static class TestImages
             public const string HangBadScan = "Jpg/issues/Hang_C438A851.jpg";
             public const string Issue2517 = "Jpg/issues/issue2517-bad-d7.jpg";
             public const string Issue2638 = "Jpg/issues/Issue2638.jpg";
+            public const string Issue2758 = "Jpg/issues/issue-2758.jpg";
 
             public static class Fuzz
             {

tests/Images/Input/Jpg/issues/issue-2758.jpg

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:f32a238b57b7073f7442f8ae7efd6ba3ae4cda30d57e6666fb8a1eaa27108558
+size 1412