From cf2e641000c832f3bdb0ff55b6e19ba6798a8f4a Mon Sep 17 00:00:00 2001
From: Dirk Lemstra <dirk@git.imagemagick.org>
Date: Thu, 6 Sep 2018 22:27:28 +0200
Subject: [PATCH] Allow several invalid data types when reading the exif
 resolution.

---
 .../Formats/Jpeg/JpegDecoderCore.cs           | 29 ++++++++++++++-----
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
index 7561afa1e..cd960a241 100644
--- a/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
+++ b/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs
@@ -463,13 +463,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             }
             else if (this.isExif)
             {
-                double horizontalValue = this.MetaData.ExifProfile.TryGetValue(ExifTag.XResolution, out ExifValue horizontalTag)
-                    ? ((Rational)horizontalTag.Value).ToDouble()
-                    : 0;
-
-                double verticalValue = this.MetaData.ExifProfile.TryGetValue(ExifTag.YResolution, out ExifValue verticalTag)
-                    ? ((Rational)verticalTag.Value).ToDouble()
-                    : 0;
+                double horizontalValue = this.GetExifResolutionValue(ExifTag.XResolution);
+                double verticalValue = this.GetExifResolutionValue(ExifTag.YResolution);
 
                 if (horizontalValue > 0 && verticalValue > 0)
                 {
@@ -480,6 +475,26 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             }
         }
 
+        private double GetExifResolutionValue(ExifTag tag)
+        {
+            if (!this.MetaData.ExifProfile.TryGetValue(tag, out ExifValue exifValue))
+            {
+                return 0;
+            }
+
+            switch (exifValue.DataType)
+            {
+                case ExifDataType.Rational:
+                    return ((Rational)exifValue.Value).ToDouble();
+                case ExifDataType.Long:
+                    return (uint)exifValue.Value;
+                case ExifDataType.DoubleFloat:
+                    return (double)exifValue.Value;
+                default:
+                    return 0;
+            }
+        }
+
         /// <summary>
         /// Extends the profile with additional data.
         /// </summary>