Decode and re-encode a PNG for timing purposes

png-reencode.go

package main

import (
			 "bytes"
			 "fmt"
			 "image/png"
			 "io/ioutil"
			 "time"
)

func check(e error) {
		 if e != nil {
		 		panic(e)
		 }
}

func main() {
		 data, err := ioutil.ReadFile("depth.png")
		 check(err)

		 for i := 0; i < 10; i++ {
		 		 start := time.Now()
				 reencode(data)
				 fmt.Printf("Decode-encode cycle took %s.\n", time.Since(start))
		 }

		 err = ioutil.WriteFile("re-encoded.png", reencode(data).Bytes(), 0666)
		 check(err)
}

func reencode(data []byte) *bytes.Buffer {
 		 img, err := png.Decode(bytes.NewReader(data))
 		 check(err)

 		 buf := &bytes.Buffer{}
 		 err = png.Encode(buf, img)
 		 check(err)

		 return buf
}

Above Go code:

$ ./png-reencode                                        
Decode-encode cycle took 1.277722854s.                                                  
Decode-encode cycle took 1.213648088s.
Decode-encode cycle took 1.199818711s. 
Decode-encode cycle took 1.191781526s.                                            
Decode-encode cycle took 1.24086317s.                                                                      
Decode-encode cycle took 1.194477502s.
Decode-encode cycle took 1.172427988s.
Decode-encode cycle took 1.189565899s.                                   
Decode-encode cycle took 1.16677147s.
Decode-encode cycle took 1.279670013s.

PNG header injector

import copy
import cStringIO
import io
import sys
import time

import png_header_injector


ITERATIONS = 10


def main(input_path):
    use_header_injector(input_path)


def use_header_injector(input_path):
    with open(input_path, "rb") as png:
        inp = png.read(-1)

    for i in range(ITERATIONS):
        img_data = cStringIO.StringIO(copy.copy(inp))
        out = io.BytesIO()

        start = time.time()

        png_header_injector.replace_text(
            img_data, out, {"Comment": "Test comment data."})

        end = time.time()

        print(
            "Header injector total time: %0.4f seconds." % (end - start))


if __name__ == "__main__":
    main(sys.argv[1])

Timing:

$ python png-injector.py ~/dev/go-tests/zed-depth.png 
Header injector total time: 0.0007 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.
Header injector total time: 0.0001 seconds.