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// Copyright 2026 Rose Hogenson <r@roseh.moe>
//
// This file is part of imgutil.
//
// Imgutil is free software: you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the Free Software
// Foundation, either version 3 of the License, or (at your option) any later
// version.
//
// Imgutil is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
// FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
// details.
//
// You should have received a copy of the GNU General Public License along with
// imgutil. If not, see <https://www.gnu.org/licenses/>.
package main
import (
"errors"
"flag"
"fmt"
"image"
"image/gif"
"image/jpeg"
"image/png"
"os"
"strings"
"golang.org/x/image/bmp"
"golang.org/x/image/draw"
"golang.org/x/image/tiff"
_ "golang.org/x/image/webp"
)
var (
x = flag.Int("x", 0, "new image width")
y = flag.Int("y", 0, "new image height")
stretch = flag.Bool("stretch", false, "if resizing, whether to stretch the image rather than cropping (the default)")
format = flag.String("format", "", "output image format, default is to use the file extension")
)
func load(filename string) (image.Image, error) {
file := os.Stdin
if filename != "-" {
var err error
file, err = os.Open(filename)
if err != nil {
return nil, err
}
defer file.Close()
}
img, _, err := image.Decode(file)
if err != nil {
return nil, fmt.Errorf("decode %q: %s", filename, err)
}
return img, nil
}
func divRound(n, d int) int {
return (n + d/2) / d
}
func resize(img image.Image) image.Image {
x, y := *x, *y
if x == 0 {
x = divRound(y*img.Bounds().Dx(), img.Bounds().Dy())
}
if y == 0 {
y = divRound(x*img.Bounds().Dy(), img.Bounds().Dx())
}
output := image.NewRGBA64(image.Rect(0, 0, x, y))
srcRect := img.Bounds()
if !*stretch {
if img.Bounds().Dx()*y >= img.Bounds().Dy()*x {
scaledX := divRound(img.Bounds().Dy()*x, y)
xOffset := (img.Bounds().Dx() - scaledX) / 2
srcRect.Min.X += xOffset
srcRect.Max.X = srcRect.Min.X + scaledX
} else {
scaledY := divRound(img.Bounds().Dx()*y, x)
yOffset := (img.Bounds().Dy() - scaledY) / 2
srcRect.Min.Y += yOffset
srcRect.Max.Y = srcRect.Min.Y + scaledY
}
}
draw.CatmullRom.Scale(output, output.Bounds(), img, srcRect, draw.Src, nil)
return output
}
func run() error {
args := flag.Args()
if len(args) != 2 {
return errors.New("usage: convert input-file output-file")
}
inputFileName, outputFileName := args[0], args[1]
ext := *format
if ext == "" {
n := strings.LastIndex(outputFileName, ".")
if n < 0 {
return errors.New("unknown output file extension")
}
ext = outputFileName[n+1:]
}
switch ext {
case "gif", "jpeg", "jpg", "png", "bmp", "tiff":
default:
return fmt.Errorf("unknown output file extension %q", ext)
}
input, err := load(inputFileName)
if err != nil {
return err
}
if *x != 0 || *y != 0 {
input = resize(input)
}
outputFile, err := os.Create(outputFileName)
if err != nil {
return err
}
defer outputFile.Close()
switch ext {
case "gif":
err = gif.Encode(outputFile, input, nil)
case "jpeg", "jpg":
err = jpeg.Encode(outputFile, input, &jpeg.Options{Quality: 100})
case "png":
err = png.Encode(outputFile, input)
case "bmp":
err = bmp.Encode(outputFile, input)
case "tiff":
err = tiff.Encode(outputFile, input, nil)
}
if err != nil {
return err
}
return outputFile.Close()
}
func main() {
flag.Usage = func() {
fmt.Fprint(os.Stderr, `Usage: convert input-file output-file
Supported formats:
png
jpeg
bmp
tiff
webp (input only)
`)
flag.PrintDefaults()
}
flag.Parse()
if err := run(); err != nil {
fmt.Fprintf(os.Stderr, "convert: %s\n", err)
os.Exit(1)
}
}
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