diff --git a/ofdgo.go b/ofdgo.go
index ce90a32..9d852c5 100644
--- a/ofdgo.go
+++ b/ofdgo.go
@@ -76,6 +76,7 @@ func NewRenderer(reader *Reader, opts ...RendererOption) *Renderer {
 		fontCache:             make(map[fontCacheKey]*canvas.FontFamily),
 		fontSourceCache:       make(map[string][]fontSource),
 		fontSourceUsed:        make(map[string]fontSource),
+		fontDirCandidates:     make(map[string][]fontFileCandidate),
 		textGlyphPathCache:    make(map[textGlyphPathCacheKey]textGlyphPathCacheValue),
 		templatePageCache:     make(map[string]*PageContent),
 	}
diff --git a/ofdgo_font_loader.go b/ofdgo_font_loader.go
index a343b28..2997745 100644
--- a/ofdgo_font_loader.go
+++ b/ofdgo_font_loader.go
@@ -250,8 +250,12 @@ func (r *Renderer) loadFontSource(family *canvas.FontFamily, source fontSource,
 // 入参: dir 目录, patterns 模式列表, bold 是否粗体, italic 是否斜体
 // 返回: []string 文件列表
 func (r *Renderer) matchFontFiles(dir string, patterns []string, bold, italic bool) []string {
-	files, _ := filepath.Glob(filepath.Join(dir, "*"))
-	candidates := fontFileCandidates(files, filepath.Base)
+	candidates, ok := r.fontDirCandidates[dir]
+	if !ok {
+		files, _ := filepath.Glob(filepath.Join(dir, "*"))
+		candidates = fontFileCandidates(files, filepath.Base)
+		r.fontDirCandidates[dir] = candidates
+	}
 	matches := make([]fontFileMatch, 0, len(candidates))
 	index := make(map[string]int, len(candidates))
 	for _, matcher := range newFontPatternMatchers(patterns) {
diff --git a/ofdgo_renderer.go b/ofdgo_renderer.go
index 5446273..df42c22 100644
--- a/ofdgo_renderer.go
+++ b/ofdgo_renderer.go
@@ -36,6 +36,7 @@ type Renderer struct {
 	fontCache             map[fontCacheKey]*canvas.FontFamily
 	fontSourceCache       map[string][]fontSource
 	fontSourceUsed        map[string]fontSource
+	fontDirCandidates     map[string][]fontFileCandidate
 	textGlyphPathCache    map[textGlyphPathCacheKey]textGlyphPathCacheValue
 	templatePageCache     map[string]*PageContent
 	fontDirs              []string
diff --git a/ofdgo_renderer_image.go b/ofdgo_renderer_image.go
index e0ab8e9..4e6d0fd 100644
--- a/ofdgo_renderer_image.go
+++ b/ofdgo_renderer_image.go
@@ -266,28 +266,46 @@ func imageWithTransparentEdge(img image.Image) (image.Image, int) {
 	if opaque, ok := source.(interface{ Opaque() bool }); ok && opaque.Opaque() {
 		return img, 0
 	}
-	src := image.NewNRGBA(image.Rect(0, 0, w, h))
 	hasZero, hasVisible := false, false
-	for y := 0; y < h; y++ {
-		for x := 0; x < w; x++ {
-			c := imageNRGBAAt(source, bounds.Min.X+x, bounds.Min.Y+y)
-			src.SetNRGBA(x, y, c)
-			if c.A == 0 {
-				hasZero = true
-			} else {
-				hasVisible = true
+	src, ok := source.(*image.NRGBA)
+	if ok {
+		srcBounds := src.Bounds()
+		for y := srcBounds.Min.Y; y < srcBounds.Max.Y; y++ {
+			offset := src.PixOffset(srcBounds.Min.X, y) + 3
+			for x := 0; x < w; x++ {
+				if src.Pix[offset] == 0 {
+					hasZero = true
+				} else {
+					hasVisible = true
+				}
+				offset += 4
+			}
+		}
+	} else {
+		src = image.NewNRGBA(image.Rect(0, 0, w, h))
+		for y := 0; y < h; y++ {
+			for x := 0; x < w; x++ {
+				c := imageNRGBAAt(source, bounds.Min.X+x, bounds.Min.Y+y)
+				src.SetNRGBA(x, y, c)
+				if c.A == 0 {
+					hasZero = true
+				} else {
+					hasVisible = true
+				}
 			}
 		}
 	}
 	if !hasZero || !hasVisible {
 		return img, 0
 	}
+	srcBounds := src.Bounds()
 	out := image.NewNRGBA(image.Rect(0, 0, w+2, h+2))
 	for y := 0; y < h; y++ {
 		for x := 0; x < w; x++ {
-			c := src.NRGBAAt(x, y)
+			sx, sy := srcBounds.Min.X+x, srcBounds.Min.Y+y
+			c := src.NRGBAAt(sx, sy)
 			if c.A == 0 {
-				if edge, ok := transparentEdgeColor(src, x, y); ok {
+				if edge, ok := transparentEdgeColor(src, sx, sy); ok {
 					c = edge
 				}
 			}