Golang x/image/webp: unable to decode image

What version of Go are you using (`go version`)?

go version go1.20.4 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (`go env`)?

go env Output

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jmooring/.cache/go-build"
GOENV="/home/jmooring/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/jmooring/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jmooring/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/snap/go/current"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/snap/go/current/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.20.4"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-O2 -g"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-O2 -g"
CGO_FFLAGS="-O2 -g"
CGO_LDFLAGS="-O2 -g"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build960738136=/tmp/go-build -gno-record-gcc-switches"

What did you do?

main.go

package main

import (
    "fmt"
    "image"
    "log"
    "os"

    _ "golang.org/x/image/webp"
)

func main() {
    reader, err := os.Open(os.Args[1])
    if err != nil {
        log.Fatal(err)
    }

    m, _, err := image.Decode(reader)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("Successfully decoded %s. Image bounds: %s\n", os.Args[1], m.Bounds())
}

go run . test.webp

What did you expect to see?

Successfully decoded test.webp. Image bounds: (0,0)-(210,210)

What did you see instead?

2023/05/25 11:56:07 webp: invalid format
exit status 1

Notes

This is not an animated WebP image.

This image is not corrupt:

It displays as expected in Chrome and Firefox
It displays as expected in Microsoft Visual Studio Code
It can be converted with cwebp
It can be processed with ImageMagick
It can be processed with exiftool

Test image

test.webp

Comment From: jespino

I've been investigating a bit on this issue, and I want to provide some extra info here:

It looks like related to the Alpha Channel. The webpinfo command gives me the following output:

File: test.webp
RIFF HEADER:
  File size:  58606
Chunk VP8X at offset     12, length     18
  ICCP: 1
  Alpha: 1
  EXIF: 0
  XMP: 0
  Animation: 0
  Canvas size 210 x 210
Chunk ICCP at offset     30, length    680
Chunk VP8L at offset    710, length  57896
  Width: 210
  Height: 210
  Alpha: 1
  Animation: 0
  Format: Lossless (2)
No error detected.

This is saying that there are three chunks. The first one is the VP8X, which works fine. The second one, the ICCP (The Color Profile), is not implemented in the decoder, and the third one is a VP8L chunk, and because we already declared that we need Alpha, we will check if the Alpha channel is defined. Because we ignore the ICCP, there is no alpha channel defined.

If you use image magick to convert from that file to png and back to webp, the webpinfo command gives the following info:

File: test2.webp
RIFF HEADER:
  File size:  14520
Chunk VP8X at offset     12, length     18
  ICCP: 1
  Alpha: 1
  EXIF: 0
  XMP: 0
  Animation: 0
  Canvas size 210 x 210
Chunk ICCP at offset     30, length    680
Chunk ALPH at offset    710, length   3308
Chunk VP8  at offset   4018, length  10502
  Width: 210
  Height: 210
  Alpha: 0
  Animation: 0
  Format: Lossy (1)
No error detected.

The main difference is the ALPH chunk is there, so it works perfectly now.

From the code perspective, what happens is that the alpha variable is not initialized before the VP8L chunk is processed.

Comment From: jespino

I'm looking into it more. Reading the specification, the VP8L frame already contains the alpha information. You can read that here: https://developers.google.com/speed/webp/docs/riff_container?hl=es-419#alpha (almost at the end of that section).

So I guess adding support to read the alpha information from the VP8L chunk, should fix this.

Comment From: gopherbot

Change https://go.dev/cl/498535 mentions this issue: Allow to use VP8L+ICC in the same file without APLH chunk

Comment From: cristaloleg

I can confirm this issue is still relevant and that the proposed fix is valid https://github.com/golang/image/pull/16

What version of Go are you using (go version)?