commit ca6ba492690135647443817ba0d3ccb0c2f0de14
author Nigel Tao <nigeltao@golang.org> Sun Jul 12 21:02:13 2015 +1000
committer Nigel Tao <nigeltao@golang.org> Mon Jul 13 06:40:00 2015 +0000
tree 60d2ab405bdc32036525ef96bf3d7c27ef813724
parent 616cb3c0eadada458358d69b1098a5aea9165099

image/png: don't read filter bytes for empty interlace passes.

Fixes #11604

The gray-gradient.png image was created by a Go program:

----
package main

import (
	"image"
	"image/color"
	"image/png"
	"log"
	"os"
)

func main() {
	f, err := os.Create("a.png")
	if err != nil {
		log.Fatal(err)
	}
	defer f.Close()
	m := image.NewGray(image.Rect(0, 0, 1, 16))
	for i := 0; i < 16; i++ {
		m.SetGray(0, i, color.Gray{uint8(i * 0x11)})
	}
	err = png.Encode(f, m)
	if err != nil {
		log.Fatal(err)
	}
}
----

The equivalent gray-gradient.interlaced.png image was created via ImageMagick:
$ convert -interlace PNG gray-gradient.png gray-gradient.interlaced.png

As a sanity check:
$ file gray-gradient.*
gray-gradient.interlaced.png: PNG image data, 1 x 16, 4-bit grayscale, interlaced
gray-gradient.png:            PNG image data, 1 x 16, 8-bit grayscale, non-interlaced

Change-Id: I7700284f74d1ea30073aede3bce4d7651787bdbc
Reviewed-on: https://go-review.googlesource.com/12064
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>