Handle Indexed Pixel Format correctly in Image Resize transform. (#3601)

* Handle Indexed Pixel Format correctly in Image Resize transform.

* PR feedback.

* PR feedback.

* PR feedback.

* PR feedback.

Author: codemzs

src/Microsoft.ML.ImageAnalytics/ImageResizer.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.Drawing;
+using System.Drawing.Imaging;
 using System.Linq;
 using System.Text;
 using Microsoft.ML;
@@ -381,7 +382,13 @@ protected override Delegate MakeGetter(DataViewRow input, int iinfo, Func<int, b
                             destHeight = info.ImageHeight;
                         }
 
-                        dst = new Bitmap(info.ImageWidth, info.ImageHeight, src.PixelFormat);
+                        // Graphics.DrawImage() does not support PixelFormat.Indexed. Hence convert the
+                        // pixel format to Format32bppArgb as described here https://stackoverflow.com/questions/17313285/graphics-on-indexed-image
+                        if ((src.PixelFormat & PixelFormat.Indexed) != 0)
+                            dst = new Bitmap(info.ImageWidth, info.ImageHeight);
+                        else
+                            dst = new Bitmap(info.ImageWidth, info.ImageHeight, src.PixelFormat);
+
                         var srcRectangle = new Rectangle(sourceX, sourceY, sourceWidth, sourceHeight);
                         var destRectangle = new Rectangle(destX, destY, destWidth, destHeight);
                         using (var g = Graphics.FromImage(dst))

test/Microsoft.ML.Tests/ScenariosWithDirectInstantiation/TensorflowTests.cs

@@ -845,7 +845,7 @@ public void TensorFlowTransformCifar()
             var imageHeight = type.Dimensions[0];
             var imageWidth = type.Dimensions[1];
 
-            var dataFile = GetDataPath("images/images.tsv");
+            var dataFile = GetDataPath("images/imagesmixedpixelformat.tsv");
             var imageFolder = Path.GetDirectoryName(dataFile);
             var data = mlContext.Data.LoadFromTextFile(dataFile,
                 columns: new[]
@@ -874,7 +874,7 @@ public void TensorFlowTransformCifar()
                     Assert.Equal(10, buffer.Length);
                     numRows += 1;
                 }
-                Assert.Equal(4, numRows);
+                Assert.Equal(5, numRows);
             }
         }
 

test/data/images/imagesmixedpixelformat.tsv

@@ -0,0 +1,5 @@
+tomato.bmp	tomato
+banana.jpg	banana
+hotdog.jpg	hotdog
+tomato.jpg	tomato
+tomato_indexedpixelformat.gif	tomato