fix: Optimize PNG compression for large files.

Author: Christopher Murphy

CLAUDE.md

@@ -56,7 +56,7 @@ Vue 2 + Vuex. `App.vue` is the root with a sidebar + view router pattern (no vue
 Key components: `Editor.vue` (drag-drop + file list), `Settings.vue` (quality/size/format config), `Stats.vue` (lifetime stats display).
 
 ## Key Dependencies
-- **Go**: `wailsapp/wails/v2`, `chai2010/webp`, `disintegration/imaging`, `muesli/smartcrop`, `foobaz/lossypng`
+- **Go**: `wailsapp/wails/v2`, `chai2010/webp`, `disintegration/imaging`, `muesli/smartcrop`
 - **JS**: Vue 2.6, Vuex 3, Tailwind CSS 1.9
 
 ## Wails v2 Notes

backend/image/file.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"time"
 
 	"github.com/disintegration/imaging"
 	"github.com/muesli/smartcrop"
@@ -130,14 +131,20 @@ func (f *File) Write(c *config.Config, ctx context.Context) error {
 			}
 		}
 	}
+	t0 := time.Now()
 	buf, err := encToBuf(f.Image, c.App)
+	runtime.LogInfof(ctx, "perf: encode %s (%dx%d) to %s: %s", f.Name,
+		f.Image.Bounds().Max.X, f.Image.Bounds().Max.Y,
+		c.App.Target, time.Since(t0))
 	dest := path.Join(c.App.OutDir, c.App.Prefix+f.Name+c.App.Suffix+"."+c.App.Target)
 	if err != nil {
 		return err
 	}
+	t1 := time.Now()
 	if err = os.WriteFile(dest, buf.Bytes(), 0666); err != nil {
 		return err
 	}
+	runtime.LogInfof(ctx, "perf: write %s (%d bytes): %s", dest, len(buf.Bytes()), time.Since(t1))
 	f.ConvertedFile = filepath.Clean(dest)
 	f.IsConverted = true
 	return nil

backend/image/filemanager.go

@@ -110,6 +110,7 @@ func (fm *FileManager) SelectFiles() ([]SelectFileMeta, error) {
 			runtime.LogErrorf(fm.ctx, "failed to decode file %s: %v", p, err)
 			continue
 		}
+		file.Data = nil // release raw bytes; image is now in file.Image
 		fm.Files = append(fm.Files, file)
 		runtime.LogInfof(fm.ctx, "added file to file manager via dialog: %s", file.Name)
 

backend/png/png.go

@@ -2,14 +2,11 @@ package png
 
 import (
 	"bytes"
-	"github.com/foobaz/lossypng/lossypng"
 	"image"
 	"image/png"
 	"io"
 )
 
-const qMax = 20
-
 // Options represent PNG encoding options.
 type Options struct {
 	Quality int `json:"quality"`
@@ -25,15 +22,23 @@ func DecodePNG(r io.Reader) (image.Image, error) {
 }
 
 // EncodePNG encodes an image into PNG and returns a buffer.
+// Lossless compression is used; the Quality option controls the compression
+// level (higher quality = less compression effort = faster encode).
 func EncodePNG(i image.Image, o *Options) (buf bytes.Buffer, err error) {
-	c := lossypng.Compress(i, 2, qualityFactor(o.Quality))
-	err = png.Encode(&buf, c)
+	enc := &png.Encoder{CompressionLevel: compressionLevel(o.Quality)}
+	err = enc.Encode(&buf, i)
 	return buf, err
 }
 
-// qualityFactor normalizes the PNG quality factor from a max of 20, where 0 is
-// no conversion.
-func qualityFactor(q int) int {
-	f := q / 100
-	return qMax - (f * qMax)
+// compressionLevel maps a quality value (0–100) to a png.CompressionLevel.
+// Lower quality = more aggressive compression (smaller file, slower encode).
+func compressionLevel(q int) png.CompressionLevel {
+	switch {
+	case q >= 80:
+		return png.BestSpeed
+	case q >= 40:
+		return png.DefaultCompression
+	default:
+		return png.BestCompression
+	}
 }

backend/webp/webp.go

@@ -13,7 +13,7 @@ type Options struct {
 	Quality  int  `json:"quality"`
 }
 
-// DecodeWebp a webp file and return an image.
+// DecodeWebp decodes a webp file and returns an image.
 func DecodeWebp(r io.Reader) (image.Image, error) {
 	i, err := webp.Decode(r)
 	if err != nil {
@@ -22,7 +22,7 @@ func DecodeWebp(r io.Reader) (image.Image, error) {
 	return i, nil
 }
 
-// EncodeWebp encodes an image into webp and returns a buffer.
+// EncodeWebp encodes an image into WebP and returns a buffer.
 func EncodeWebp(i image.Image, o *Options) (buf bytes.Buffer, err error) {
 	if err = webp.Encode(&buf, i, &webp.Options{Lossless: o.Lossless, Quality: float32(o.Quality)}); err != nil {
 		return buf, err

go.mod

@@ -5,7 +5,6 @@ go 1.22.0
 require (
 	github.com/chai2010/webp v1.1.0
 	github.com/disintegration/imaging v1.6.2
-	github.com/foobaz/lossypng v0.0.0-20200814224715-48fa8819852a
 	github.com/muesli/smartcrop v0.3.0
 	github.com/vrischmann/userdir v0.0.0-20151206171402-20f291cebd68
 	github.com/wailsapp/wails/v2 v2.11.0

go.sum

@@ -6,8 +6,6 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/disintegration/imaging v1.6.2 h1:w1LecBlG2Lnp8B3jk5zSuNqd7b4DXhcjwek1ei82L+c=
 github.com/disintegration/imaging v1.6.2/go.mod h1:44/5580QXChDfwIclfc/PCwrr44amcmDAg8hxG0Ewe4=
-github.com/foobaz/lossypng v0.0.0-20200814224715-48fa8819852a h1:0TYY/syyvt/+y5PWAkybgG2o6zHY+UrI3fuixaSeRoI=
-github.com/foobaz/lossypng v0.0.0-20200814224715-48fa8819852a/go.mod h1:wRxTcIExb9GZAgOr1wrQuOZBkyoZNQi7znUmeyKTciA=
 github.com/go-ole/go-ole v1.3.0 h1:Dt6ye7+vXGIKZ7Xtk4s6/xVdGDQynvom7xCFEdWr6uE=
 github.com/go-ole/go-ole v1.3.0/go.mod h1:5LS6F96DhAwUc7C+1HLexzMXY1xGRSryjyPPKW6zv78=
 github.com/godbus/dbus/v5 v5.1.0 h1:4KLkAxT3aOY8Li4FRJe/KvhoNFFxo0m6fNuFUO8QJUk=