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https://github.com/gopl-zh/gopl-zh.github.com.git
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53 lines
1016 B
Go
53 lines
1016 B
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 287.
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//!+main
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// The jpeg command reads a PNG image from the standard input
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// and writes it as a JPEG image to the standard output.
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package main
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import (
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"fmt"
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"image"
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"image/jpeg"
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_ "image/png" // register PNG decoder
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"io"
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"os"
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)
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func main() {
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if err := toJPEG(os.Stdin, os.Stdout); err != nil {
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fmt.Fprintf(os.Stderr, "jpeg: %v\n", err)
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os.Exit(1)
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}
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}
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func toJPEG(in io.Reader, out io.Writer) error {
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img, kind, err := image.Decode(in)
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if err != nil {
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return err
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}
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fmt.Fprintln(os.Stderr, "Input format =", kind)
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return jpeg.Encode(out, img, &jpeg.Options{Quality: 95})
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}
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//!-main
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/*
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//!+with
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$ go build gopl.io/ch3/mandelbrot
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$ go build gopl.io/ch10/jpeg
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$ ./mandelbrot | ./jpeg >mandelbrot.jpg
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Input format = png
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//!-with
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//!+without
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$ go build gopl.io/ch10/jpeg
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$ ./mandelbrot | ./jpeg >mandelbrot.jpg
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jpeg: image: unknown format
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//!-without
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*/
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