115 lines
3.2 KiB
Go
115 lines
3.2 KiB
Go
package utils
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import (
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"bytes"
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"encoding/base64"
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"fmt"
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"image"
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"image/gif"
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"image/jpeg"
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"net/http"
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"golang.org/x/image/draw"
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)
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// CompressImage takes a base‑64‑encoded image (JPEG, PNG or GIF) and returns
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// a base‑64‑encoded version that is at most maxLength in size, or an error.
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func CompressImage(b64 string, maxLength int) (string, string, error) {
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raw, err := base64.StdEncoding.DecodeString(b64)
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if err != nil {
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return "", "", fmt.Errorf("base64 decode: %w", err)
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}
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mime := http.DetectContentType(raw)
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if len(raw) <= maxLength {
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return b64, mime, nil // small enough already
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}
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switch mime {
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case "image/gif":
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return compressGIF(raw, maxLength)
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default: // jpeg, png, webp, etc. → treat as raster
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return compressRaster(raw, maxLength)
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}
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}
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// ---------- Raster path (jpeg / png / single‑frame gif) ----------
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func compressRaster(src []byte, maxLength int) (string, string, error) {
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img, _, err := image.Decode(bytes.NewReader(src))
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if err != nil {
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return "", "", fmt.Errorf("decode raster: %w", err)
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}
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quality := 95
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for {
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var buf bytes.Buffer
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if err := jpeg.Encode(&buf, img, &jpeg.Options{Quality: quality}); err != nil {
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return "", "", fmt.Errorf("jpeg encode: %w", err)
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}
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if buf.Len() <= maxLength {
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return base64.StdEncoding.EncodeToString(buf.Bytes()), "image/jpeg", nil
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}
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if quality > 20 {
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quality -= 5
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continue
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}
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// down‑scale 80%
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b := img.Bounds()
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if b.Dx() < 100 || b.Dy() < 100 {
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return "", "", fmt.Errorf("cannot compress below %.02fMiB without destroying image", float64(maxLength)/1048576.0)
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}
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dst := image.NewRGBA(image.Rect(0, 0, int(float64(b.Dx())*0.8), int(float64(b.Dy())*0.8)))
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draw.ApproxBiLinear.Scale(dst, dst.Bounds(), img, b, draw.Over, nil)
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img = dst
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quality = 95 // restart ladder
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}
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}
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// ---------- Animated GIF path ----------
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func compressGIF(src []byte, maxLength int) (string, string, error) {
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g, err := gif.DecodeAll(bytes.NewReader(src))
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if err != nil {
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return "", "", fmt.Errorf("gif decode: %w", err)
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}
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for {
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var buf bytes.Buffer
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if err := gif.EncodeAll(&buf, g); err != nil {
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return "", "", fmt.Errorf("gif encode: %w", err)
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}
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if buf.Len() <= maxLength {
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return base64.StdEncoding.EncodeToString(buf.Bytes()), "image/gif", nil
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}
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// down‑scale every frame by 80%
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w, h := g.Config.Width, g.Config.Height
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if w < 100 || h < 100 {
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return "", "", fmt.Errorf("cannot compress animated GIF below 5 MiB without excessive quality loss")
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}
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nw, nh := int(float64(w)*0.8), int(float64(h)*0.8)
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for i, frm := range g.Image {
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// convert paletted frame → RGBA for scaling
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rgba := image.NewRGBA(frm.Bounds())
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draw.Draw(rgba, rgba.Bounds(), frm, frm.Bounds().Min, draw.Src)
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// scaled destination
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dst := image.NewRGBA(image.Rect(0, 0, nw, nh))
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draw.ApproxBiLinear.Scale(dst, dst.Bounds(), rgba, rgba.Bounds(), draw.Over, nil)
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// quantize back to paletted using default encoder quantizer
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paletted := image.NewPaletted(dst.Bounds(), nil)
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draw.FloydSteinberg.Draw(paletted, paletted.Bounds(), dst, dst.Bounds().Min)
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g.Image[i] = paletted
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}
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g.Config.Width, g.Config.Height = nw, nh
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// loop back and test size again …
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}
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}
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