feat(pdfengines): optimize PDF images to reduce file size (#359)

pkg/modules/pdfcpu/optimize_test.go

@@ -0,0 +1,83 @@
+package pdfcpu
+
+import "testing"
+
+const sampleImagesList = `pages: all
+
+/tmp/multi.pdf:
+4 images available (8.9 MB)
+Page │ Obj# │ Id  │ Type  SoftMask ImgMask │ Width │ Height │ ColorSpace Comp bpc Interp │   Size │ Filters
+━━━━━┿━━━━━━┿━━━━━┿━━━━━━━━━━━━━━━━━━━━━━━━┿━━━━━━━┿━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━━━━━━━━━┿━━━━━━━━┿━━━━━━━━━━━━
+   1 │    6 │  X6 │ image                  │  2400 │   1800 │   ICCBased    3   8        │ 5.5 MB │ FlateDecode
+     │    8 │  X8 │ image    *             │  1400 │   1000 │   ICCBased    3   8        │  63 KB │ FlateDecode
+     │    9 │  X9 │ image                  │  2400 │   1800 │   ICCBased    3   8        │ 194 KB │ DCTDecode
+     │   10 │ X10 │ image                  │   120 │     90 │ DeviceCMYK    4   8        │  14 KB │ FlateDecode
+`
+
+func TestParseImagesList(t *testing.T) {
+	images := parseImagesList(sampleImagesList)
+
+	if len(images) != 4 {
+		t.Fatalf("expected 4 images, got %d", len(images))
+	}
+
+	for _, tc := range []struct {
+		index  int
+		obj    int
+		id     string
+		masked bool
+		comp   int
+		filter string
+	}{
+		{0, 6, "X6", false, 3, "FlateDecode"},
+		{1, 8, "X8", true, 3, "FlateDecode"},
+		{2, 9, "X9", false, 3, "DCTDecode"},
+		{3, 10, "X10", false, 4, "FlateDecode"},
+	} {
+		img := images[tc.index]
+		if img.obj != tc.obj || img.id != tc.id || img.masked != tc.masked || img.comp != tc.comp || img.filter != tc.filter {
+			t.Errorf("image %d = %+v, want obj=%d id=%s masked=%v comp=%d filter=%s",
+				tc.index, img, tc.obj, tc.id, tc.masked, tc.comp, tc.filter)
+		}
+	}
+}
+
+func TestParseHumanSize(t *testing.T) {
+	for _, tc := range []struct {
+		cell string
+		want int64
+	}{
+		{"5.5 MB", int64(5.5 * (1 << 20))},
+		{"194 KB", 194 << 10},
+		{" 14 KB ", 14 << 10},
+		{"512 B", 512},
+		{"2 GB", 2 << 30},
+		{"", 0},
+		{"garbage", 0},
+	} {
+		if got := parseHumanSize(tc.cell); got != tc.want {
+			t.Errorf("parseHumanSize(%q) = %d, want %d", tc.cell, got, tc.want)
+		}
+	}
+}
+
+func TestOptimizableImage(t *testing.T) {
+	base := pdfcpuImage{obj: 1, id: "X1", masked: false, comp: 3, bytes: 1 << 20, filter: "FlateDecode"}
+
+	for _, tc := range []struct {
+		scenario string
+		mutate   func(pdfcpuImage) pdfcpuImage
+		want     bool
+	}{
+		{"lossless RGB above threshold", func(i pdfcpuImage) pdfcpuImage { return i }, true},
+		{"already compressed", func(i pdfcpuImage) pdfcpuImage { i.filter = "DCTDecode"; return i }, false},
+		{"CMYK", func(i pdfcpuImage) pdfcpuImage { i.comp = 4; return i }, false},
+		{"masked", func(i pdfcpuImage) pdfcpuImage { i.masked = true; return i }, false},
+		{"below threshold", func(i pdfcpuImage) pdfcpuImage { i.bytes = minOptimizeImageSize - 1; return i }, false},
+		{"grayscale above threshold", func(i pdfcpuImage) pdfcpuImage { i.comp = 1; return i }, true},
+	} {
+		if got := optimizableImage(tc.mutate(base)); got != tc.want {
+			t.Errorf("%s: optimizableImage = %v, want %v", tc.scenario, got, tc.want)
+		}
+	}
+}