Fix bug in CompareTool when pdfstream from output file has filter different from cmp file

ITXT-CR-749

Author: yulian-gaponenko

kernel/src/main/java/com/itextpdf/kernel/utils/CompareTool.java

@@ -1375,7 +1375,7 @@ private boolean compareObjects(PdfObject outObj, PdfObject cmpObj, ObjectPath cu
     }
 
     private boolean compareStreamsExtended(PdfStream outStream, PdfStream cmpStream, ObjectPath currentPath, CompareResult compareResult) {
-        boolean toDecode = PdfName.FlateDecode.equals(outStream.get(PdfName.Filter));
+        boolean toDecode = PdfName.FlateDecode.equals(outStream.get(PdfName.Filter)) && PdfName.FlateDecode.equals(cmpStream.get(PdfName.Filter));
         byte[] outStreamBytes = outStream.getBytes(toDecode);
         byte[] cmpStreamBytes = cmpStream.getBytes(toDecode);
         if (Arrays.equals(outStreamBytes, cmpStreamBytes)) {

kernel/src/test/java/com/itextpdf/kernel/utils/CompareToolTest.java

@@ -123,6 +123,19 @@ public void compareToolErrorReportTest04() throws InterruptedException, IOExcept
 
     }
 
+
+    @Test
+    public void imgFilterDiffTest() throws InterruptedException, IOException {
+        CompareTool compareTool = new CompareTool();
+        compareTool.setGenerateCompareByContentXmlReport(true);
+        String outPdf = sourceFolder + "imgFilterDiff.pdf";
+        String cmpPdf = sourceFolder + "cmp_imgFilterDiff.pdf";
+        String result = compareTool.compareByContent(outPdf, cmpPdf, destinationFolder, "difference");
+        // test that compareByContent doesn't fail with error
+        System.out.println(result);
+        Assert.assertNotNull(result);
+    }
+
     @Test
     public void differentProducerTest() throws IOException {
         String expectedMessage = "Document info fail. Expected: \"iText\u00ae <version> \u00a9<copyright years> iText Group NV (iText Software; licensed version)\", actual: \"iText\u00ae <version> \u00a9<copyright years> iText Group NV (AGPL-version)\"";