Fixing jpeg jpg determination issue

Former-commit-id: fd50b51c8cafaa33a0f99210c2279197f59b6682

src/ImageProcessor/ImageFactory.cs

@@ -38,6 +38,11 @@ namespace ImageProcessor
         /// </summary>
         private ImageFormat backupImageFormat;
 
+        /// <summary>
+        /// The original extension.
+        /// </summary>
+        private string originalExtension;
+
         /// <summary>
         /// Whether the image is indexed.
         /// </summary>
@@ -184,6 +189,7 @@ namespace ImageProcessor
                     this.JpegQuality = DefaultJpegQuality;
                     ImageFormat imageFormat = ImageUtils.GetImageFormat(imageName);
                     this.backupImageFormat = imageFormat;
+                    this.originalExtension = Path.GetExtension(imagePath);
                     this.ImageFormat = imageFormat;
                     this.isIndexed = ImageUtils.IsIndexed(this.Image);
                     this.ShouldProcess = true;
@@ -612,7 +618,7 @@ namespace ImageProcessor
                 // We need to check here if the path has an extension and remove it if so.
                 // This is so we can add the correct image format.
                 int length = filePath.LastIndexOf(".", StringComparison.Ordinal);
-                string extension = ImageUtils.GetExtensionFromImageFormat(this.ImageFormat);
+                string extension = ImageUtils.GetExtensionFromImageFormat(this.ImageFormat, this.originalExtension);
                 filePath = length == -1 ? filePath + extension : filePath.Substring(0, length) + extension;
 
                 // Fix the colour palette of indexed images.

src/ImageProcessor/Imaging/ImageUtils.cs

@@ -102,10 +102,13 @@ namespace ImageProcessor.Imaging
         /// <param name="imageFormat">
         /// The <see cref="T:System.Drawing.Imaging.ImageFormat"/> to return the extension for.
         /// </param>
+        /// <param name="originalExtension">
+        /// The original Extension.
+        /// </param>
         /// <returns>
         /// The correct file extension for the given <see cref="T:System.Drawing.Imaging.ImageFormat"/>.
         /// </returns>
-        public static string GetExtensionFromImageFormat(ImageFormat imageFormat)
+        public static string GetExtensionFromImageFormat(ImageFormat imageFormat, string originalExtension)
         {
             switch (imageFormat.ToString())
             {
@@ -117,8 +120,18 @@ namespace ImageProcessor.Imaging
                     return ".png";
                 case "Tif":
                 case "Tiff":
+                    if (!string.IsNullOrWhiteSpace(originalExtension) && originalExtension.ToUpperInvariant() == ".TIFF")
+                    {
+                        return ".tiff";
+                    }
+
                     return ".tif";
                 default:
+                    if (!string.IsNullOrWhiteSpace(originalExtension) && originalExtension.ToUpperInvariant() == ".JPEG")
+                    {
+                        return ".jpeg";
+                    }
+
                     return ".jpg";
             }
         }