golang.org/x/image/webp: PNG generated is in lower color

[ZhongUncle]

Go version

go version go1.22.0 darwin/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/Users/zhonguncle/Library/Caches/go-build'
GOENV='/Users/zhonguncle/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/zhonguncle/Desktop/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/zhonguncle/Desktop/go'
GOPRIVATE=''
GOPROXY='https://goproxy.cn'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/zhonguncle/Desktop/go/src/webp2png/go.mod'
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 -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/_j/f2g2qcw11379d43mq5rdj5jw0000gn/T/go-build1702115736=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

I write code to convert WEBP image to PNG, the code is:

go run main.go

What did you see happen?

The image is in much lower color.

I try png to png, not happened this thing. And I try Apple convert tool and dwebp in libwebp-1.4.0-mac-x86-64 to do it, they just have a little color changed.

I use digital color meter in Mac to measure them, they are actually different.

What did you expect to see?

dwebp image generated just have a little color changed.

[gabyhelp]

Related Issues and Documentation

• x/image/webp: WebP decode contrast issue #40173
• x/image/webp: issue with colors contrast when converting to jpeg/png #19672
• x/image/webp: unable to decode image #60437
• image/png: info loss when encoding non-alpha-premultiplied that's not NRGBA (e.g., NRGBA64, NYCbCrA) #26001 (closed)
• image/png: different decoding result on iOS Safari (Wasm) #32635 (closed)
• affected/package: image/jpeg "luma/chroma subsampling ratio" #60150 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[ianlancetaylor]

Looks like a dup of #40173.