diff --git a/chart.go b/chart.go
index db2df1e..7db7eee 100644
--- a/chart.go
+++ b/chart.go
@@ -1845,7 +1845,7 @@ func (f *File) addDrawingChart(sheet, drawingXML, cell string, width, height, rI
 	graphicFrame := xlsxGraphicFrame{
 		NvGraphicFramePr: xlsxNvGraphicFramePr{
 			CNvPr: &xlsxCNvPr{
-				ID:   f.countCharts() + f.countMedia() + 1,
+				ID:   len(content.OneCellAnchor) + len(content.TwoCellAnchor) + 2,
 				Name: "Chart " + strconv.Itoa(cNvPrID),
 			},
 		},
diff --git a/col.go b/col.go
index ffa0ca6..be08c29 100644
--- a/col.go
+++ b/col.go
@@ -10,6 +10,7 @@
 package excelize
 
 import (
+	"errors"
 	"math"
 	"strings"
 )
@@ -112,19 +113,22 @@ func (f *File) GetColOutlineLevel(sheet, col string) (uint8, error) {
 	for c := range xlsx.Cols.Col {
 		colData := &xlsx.Cols.Col[c]
 		if colData.Min <= colNum && colNum <= colData.Max {
-			level = colData.OutlineLevel
+			level = colData.OutlineLevel + 1
 		}
 	}
 	return level, err
 }
 
 // SetColOutlineLevel provides a function to set outline level of a single
-// column by given worksheet name and column name. For example, set outline
-// level of column D in Sheet1 to 2:
+// column by given worksheet name and column name. The value of parameter
+// 'level' is 1-7. For example, set outline level of column D in Sheet1 to 2:
 //
 //    err := f.SetColOutlineLevel("Sheet1", "D", 2)
 //
 func (f *File) SetColOutlineLevel(sheet, col string, level uint8) error {
+	if level > 7 || level < 1 {
+		return errors.New("invalid outline level")
+	}
 	colNum, err := ColumnNameToNumber(col)
 	if err != nil {
 		return err
diff --git a/col_test.go b/col_test.go
index e3164d4..a696caa 100644
--- a/col_test.go
+++ b/col_test.go
@@ -10,9 +10,7 @@ import (
 func TestColumnVisibility(t *testing.T) {
 	t.Run("TestBook1", func(t *testing.T) {
 		f, err := prepareTestBook1()
-		if !assert.NoError(t, err) {
-			t.FailNow()
-		}
+		assert.NoError(t, err)
 
 		assert.NoError(t, f.SetColVisible("Sheet1", "F", false))
 		assert.NoError(t, f.SetColVisible("Sheet1", "F", true))
@@ -38,9 +36,7 @@ func TestColumnVisibility(t *testing.T) {
 
 	t.Run("TestBook3", func(t *testing.T) {
 		f, err := prepareTestBook3()
-		if !assert.NoError(t, err) {
-			t.FailNow()
-		}
+		assert.NoError(t, err)
 		f.GetColVisible("Sheet1", "B")
 	})
 }
@@ -49,12 +45,14 @@ func TestOutlineLevel(t *testing.T) {
 	f := NewFile()
 	f.GetColOutlineLevel("Sheet1", "D")
 	f.NewSheet("Sheet2")
-	f.SetColOutlineLevel("Sheet1", "D", 4)
+	assert.NoError(t, f.SetColOutlineLevel("Sheet1", "D", 4))
 	f.GetColOutlineLevel("Sheet1", "D")
 	f.GetColOutlineLevel("Shee2", "A")
-	f.SetColWidth("Sheet2", "A", "D", 13)
-	f.SetColOutlineLevel("Sheet2", "B", 2)
-	f.SetRowOutlineLevel("Sheet1", 2, 250)
+	assert.NoError(t, f.SetColWidth("Sheet2", "A", "D", 13))
+	assert.NoError(t, f.SetColOutlineLevel("Sheet2", "B", 2))
+	assert.NoError(t, f.SetRowOutlineLevel("Sheet1", 2, 7))
+	assert.EqualError(t, f.SetColOutlineLevel("Sheet1", "D", 8), "invalid outline level")
+	assert.EqualError(t, f.SetRowOutlineLevel("Sheet1", 2, 8), "invalid outline level")
 
 	// Test set and get column outline level with illegal cell coordinates.
 	assert.EqualError(t, f.SetColOutlineLevel("Sheet1", "*", 1), `invalid column name "*"`)
@@ -67,7 +65,7 @@ func TestOutlineLevel(t *testing.T) {
 	assert.EqualError(t, f.SetRowOutlineLevel("Sheet1", 0, 1), "invalid row number 0")
 	level, err := f.GetRowOutlineLevel("Sheet1", 2)
 	assert.NoError(t, err)
-	assert.Equal(t, uint8(250), level)
+	assert.Equal(t, uint8(7), level)
 
 	_, err = f.GetRowOutlineLevel("Sheet1", 0)
 	assert.EqualError(t, err, `invalid row number 0`)
@@ -76,15 +74,10 @@ func TestOutlineLevel(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, uint8(0), level)
 
-	err = f.SaveAs(filepath.Join("test", "TestOutlineLevel.xlsx"))
-	if !assert.NoError(t, err) {
-		t.FailNow()
-	}
+	assert.NoError(t, f.SaveAs(filepath.Join("test", "TestOutlineLevel.xlsx")))
 
 	f, err = OpenFile(filepath.Join("test", "Book1.xlsx"))
-	if !assert.NoError(t, err) {
-		t.FailNow()
-	}
+	assert.NoError(t, err)
 	f.SetColOutlineLevel("Sheet2", "B", 2)
 }
 
@@ -138,11 +131,7 @@ func TestInsertCol(t *testing.T) {
 	f.SetCellHyperLink(sheet1, "A5", "https://github.com/360EntSecGroup-Skylar/excelize", "External")
 	f.MergeCell(sheet1, "A1", "C3")
 
-	err := f.AutoFilter(sheet1, "A2", "B2", `{"column":"B","expression":"x != blanks"}`)
-	if !assert.NoError(t, err) {
-		t.FailNow()
-	}
-
+	assert.NoError(t, f.AutoFilter(sheet1, "A2", "B2", `{"column":"B","expression":"x != blanks"}`))
 	assert.NoError(t, f.InsertCol(sheet1, "A"))
 
 	// Test insert column with illegal cell coordinates.
diff --git a/picture.go b/picture.go
index 518463a..4470fa1 100644
--- a/picture.go
+++ b/picture.go
@@ -272,7 +272,7 @@ func (f *File) addDrawingPicture(sheet, drawingXML, cell, file string, width, he
 	twoCellAnchor.To = &to
 	pic := xlsxPic{}
 	pic.NvPicPr.CNvPicPr.PicLocks.NoChangeAspect = formatSet.NoChangeAspect
-	pic.NvPicPr.CNvPr.ID = f.countCharts() + f.countMedia() + 1
+	pic.NvPicPr.CNvPr.ID = len(content.OneCellAnchor) + len(content.TwoCellAnchor) + 2
 	pic.NvPicPr.CNvPr.Descr = file
 	pic.NvPicPr.CNvPr.Name = "Picture " + strconv.Itoa(cNvPrID)
 	if hyperlinkRID != 0 {
diff --git a/rows.go b/rows.go
index 6281e62..3796441 100644
--- a/rows.go
+++ b/rows.go
@@ -11,6 +11,7 @@ package excelize
 
 import (
 	"encoding/xml"
+	"errors"
 	"fmt"
 	"math"
 	"strconv"
@@ -257,8 +258,8 @@ func (f *File) GetRowVisible(sheet string, row int) (bool, error) {
 }
 
 // SetRowOutlineLevel provides a function to set outline level number of a
-// single row by given worksheet name and Excel row number. For example,
-// outline row 2 in Sheet1 to level 1:
+// single row by given worksheet name and Excel row number. The value of
+// parameter 'level' is 1-7. For example, outline row 2 in Sheet1 to level 1:
 //
 //    err := f.SetRowOutlineLevel("Sheet1", 2, 1)
 //
@@ -266,6 +267,9 @@ func (f *File) SetRowOutlineLevel(sheet string, row int, level uint8) error {
 	if row < 1 {
 		return newInvalidRowNumberError(row)
 	}
+	if level > 7 || level < 1 {
+		return errors.New("invalid outline level")
+	}
 	xlsx, err := f.workSheetReader(sheet)
 	if err != nil {
 		return err
diff --git a/sparkline.go b/sparkline.go
index 314ea83..b09dbf4 100644
--- a/sparkline.go
+++ b/sparkline.go
@@ -429,11 +429,6 @@ func (f *File) AddSparkline(sheet string, opt *SparklineOption) error {
 			return err
 		}
 		for idx, ext := range decodeExtLst.Ext {
-			// hack: add back missing namespace
-			decodeExtLst.Ext[idx].XMLNSX14 = decodeExtLst.Ext[idx].X14
-			decodeExtLst.Ext[idx].XMLNSX15 = decodeExtLst.Ext[idx].X15
-			decodeExtLst.Ext[idx].XMLNSX14 = ""
-			decodeExtLst.Ext[idx].XMLNSX15 = ""
 			if ext.URI == ExtURISparklineGroups {
 				decodeSparklineGroups := decodeX14SparklineGroups{}
 				_ = xml.Unmarshal([]byte(ext.Content), &decodeSparklineGroups)
@@ -458,9 +453,8 @@ func (f *File) AddSparkline(sheet string, opt *SparklineOption) error {
 		}
 		sparklineGroupsBytes, _ := xml.Marshal(groups)
 		extLst := xlsxWorksheetExt{
-			XMLNSX14: NameSpaceSpreadSheetX14,
-			URI:      ExtURISparklineGroups,
-			Content:  string(sparklineGroupsBytes),
+			URI:     ExtURISparklineGroups,
+			Content: string(sparklineGroupsBytes),
 		}
 		extBytes, _ := xml.Marshal(extLst)
 		ws.ExtLst.Ext = string(extBytes)
diff --git a/test/Book1.xlsx b/test/Book1.xlsx
index 78431dc..d5a0591 100644
Binary files a/test/Book1.xlsx and b/test/Book1.xlsx differ
diff --git a/xmlChart.go b/xmlChart.go
index bb4b4bc..19e86e2 100644
--- a/xmlChart.go
+++ b/xmlChart.go
@@ -293,9 +293,10 @@ type cAutoTitleDeleted struct {
 type cView3D struct {
 	RotX         *attrValInt `xml:"rotX"`
 	RotY         *attrValInt `xml:"rotY"`
+	RAngAx       *attrValInt `xml:"rAngAx"`
 	DepthPercent *attrValInt `xml:"depthPercent"`
 	Perspective  *attrValInt `xml:"perspective"`
-	RAngAx       *attrValInt `xml:"rAngAx"`
+	ExtLst       *xlsxExtLst `xml:"extLst"`
 }
 
 // cPlotArea directly maps the plotArea element. This element specifies the
diff --git a/xmlStyles.go b/xmlStyles.go
index 7e02d6e..16a89ab 100644
--- a/xmlStyles.go
+++ b/xmlStyles.go
@@ -85,9 +85,6 @@ type xlsxFonts struct {
 // xlsxFont directly maps the font element. This element defines the
 // properties for one of the fonts used in this workbook.
 type xlsxFont struct {
-	Name     *attrValString `xml:"name"`
-	Charset  *attrValInt    `xml:"charset"`
-	Family   *attrValInt    `xml:"family"`
 	B        *bool          `xml:"b,omitempty"`
 	I        *bool          `xml:"i,omitempty"`
 	Strike   *bool          `xml:"strike,omitempty"`
@@ -95,9 +92,12 @@ type xlsxFont struct {
 	Shadow   *bool          `xml:"shadow,omitempty"`
 	Condense *bool          `xml:"condense,omitempty"`
 	Extend   *bool          `xml:"extend,omitempty"`
-	Color    *xlsxColor     `xml:"color"`
-	Sz       *attrValFloat  `xml:"sz"`
 	U        *attrValString `xml:"u"`
+	Sz       *attrValFloat  `xml:"sz"`
+	Color    *xlsxColor     `xml:"color"`
+	Name     *attrValString `xml:"name"`
+	Family   *attrValInt    `xml:"family"`
+	Charset  *attrValInt    `xml:"charset"`
 	Scheme   *attrValString `xml:"scheme"`
 }
 
diff --git a/xmlWorksheet.go b/xmlWorksheet.go
index 7e8cfde..fa07974 100644
--- a/xmlWorksheet.go
+++ b/xmlWorksheet.go
@@ -629,13 +629,9 @@ type xlsxLegacyDrawing struct {
 
 // xlsxWorksheetExt directly maps the ext element in the worksheet.
 type xlsxWorksheetExt struct {
-	XMLName  xml.Name `xml:"ext"`
-	XMLNSX14 string   `xml:"xmlns:x14,attr,omitempty"`
-	XMLNSX15 string   `xml:"xmlns:x15,attr,omitempty"`
-	X14      string   `xml:"x14,attr,omitempty"`
-	X15      string   `xml:"x15,attr,omitempty"`
-	URI      string   `xml:"uri,attr"`
-	Content  string   `xml:",innerxml"`
+	XMLName xml.Name `xml:"ext"`
+	URI     string   `xml:"uri,attr"`
+	Content string   `xml:",innerxml"`
 }
 
 // decodeWorksheetExt directly maps the ext element.