mirror of
https://github.com/google/wuffs.git
synced 2026-01-18 17:11:32 +01:00
cmd/handsum: new tool for the Handsum file format
This commit is contained in:
Nigel Tao
126
cmd/handsum/main.go
Normal file
126
cmd/handsum/main.go
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@@ -0,0 +1,126 @@
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// Copyright 2025 The Wuffs Authors.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//
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// SPDX-License-Identifier: Apache-2.0 OR MIT
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// ----------------
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// handsum decodes and encodes the Handsum lossy image file format.
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package main
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import (
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"bytes"
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"errors"
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"flag"
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"image"
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"image/png"
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"os"
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"github.com/google/wuffs/lib/handsum"
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_ "image/gif"
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_ "image/jpeg"
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_ "golang.org/x/image/bmp"
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_ "golang.org/x/image/tiff"
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_ "golang.org/x/image/webp"
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)
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var (
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decodeFlag = flag.Bool("decode", false, "whether to decode the input")
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encodeFlag = flag.Bool("encode", false, "whether to encode the input")
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roundtripFlag = flag.Bool("roundtrip", false, "whether to encode-and-decode the input")
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)
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const usageStr = `handsum decodes and encodes the Handsum lossy image file format.
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Usage: choose one of
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handsum -decode [path]
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handsum -encode [path]
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handsum -roundtrip [path]
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The path to the input image file is optional. If omitted, stdin is read.
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The output image (in Handsum or PNG format) is written to stdout.
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Decode inputs Handsum and outputs PNG.
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Encode inputs BMP, GIF, JPEG, PNG, TIFF or WEBP and outputs Handsum.
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Roundtrip is equivalent to encode (to an ephemeral file) and then decode.
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`
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func main() {
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if err := main1(); err != nil {
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os.Stderr.WriteString(err.Error() + "\n")
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os.Exit(1)
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}
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}
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func main1() error {
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flag.Usage = func() { os.Stderr.WriteString(usageStr) }
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flag.Parse()
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inFile := os.Stdin
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switch flag.NArg() {
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case 0:
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// No-op.
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case 1:
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f, err := os.Open(flag.Arg(0))
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if err != nil {
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return err
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}
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defer f.Close()
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inFile = f
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default:
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return errors.New("too many filenames; the maximum is one")
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}
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if *decodeFlag && !*encodeFlag && !*roundtripFlag {
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return decode(inFile)
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}
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if !*decodeFlag && *encodeFlag && !*roundtripFlag {
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return encode(inFile)
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}
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if !*decodeFlag && !*encodeFlag && *roundtripFlag {
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return roundtrip(inFile)
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}
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return errors.New("must specify exactly one of -decode, -encode, -roundtrip or -help")
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}
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func decode(inFile *os.File) error {
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src, err := handsum.Decode(inFile)
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if err != nil {
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return err
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}
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return png.Encode(os.Stdout, src)
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}
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func encode(inFile *os.File) error {
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src, _, err := image.Decode(inFile)
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if err != nil {
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return err
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}
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return handsum.Encode(os.Stdout, src)
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}
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func roundtrip(inFile *os.File) error {
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src, _, err := image.Decode(inFile)
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if err != nil {
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return err
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}
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buf := &bytes.Buffer{}
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err = handsum.Encode(buf, src)
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if err != nil {
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return err
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}
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dst, err := handsum.Decode(buf)
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if err != nil {
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return err
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}
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return png.Encode(os.Stdout, dst)
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}
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2
go.mod
2
go.mod
@@ -1,3 +1,5 @@
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module github.com/google/wuffs
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go 1.16
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require golang.org/x/image v0.24.0 // indirect
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63
go.sum
63
go.sum
@@ -0,0 +1,63 @@
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github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
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github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
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golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
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golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
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golang.org/x/crypto v0.13.0/go.mod h1:y6Z2r+Rw4iayiXXAIxJIDAJ1zMW4yaTpebo8fPOliYc=
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golang.org/x/crypto v0.19.0/go.mod h1:Iy9bg/ha4yyC70EfRS8jz+B6ybOBKMaSxLj6P6oBDfU=
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golang.org/x/crypto v0.23.0/go.mod h1:CKFgDieR+mRhux2Lsu27y0fO304Db0wZe70UKqHu0v8=
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golang.org/x/image v0.24.0 h1:AN7zRgVsbvmTfNyqIbbOraYL8mSwcKncEj8ofjgzcMQ=
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golang.org/x/image v0.24.0/go.mod h1:4b/ITuLfqYq1hqZcjofwctIhi7sZh2WaCjvsBNjjya8=
|
||||
golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
|
||||
golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
|
||||
golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
|
||||
golang.org/x/mod v0.15.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
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||||
golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
|
||||
golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
|
||||
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
|
||||
golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
|
||||
golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
|
||||
golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
|
||||
golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
|
||||
golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
|
||||
golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
|
||||
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
|
||||
golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
|
||||
golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
|
||||
golang.org/x/sync v0.3.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
|
||||
golang.org/x/sync v0.6.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
|
||||
golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
|
||||
golang.org/x/sync v0.11.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
|
||||
golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
|
||||
golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
|
||||
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
|
||||
golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
|
||||
golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
|
||||
golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
|
||||
golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
|
||||
golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
|
||||
golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
|
||||
golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
|
||||
golang.org/x/telemetry v0.0.0-20240228155512-f48c80bd79b2/go.mod h1:TeRTkGYfJXctD9OcfyVLyj2J3IxLnKwHJR8f4D8a3YE=
|
||||
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
|
||||
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
|
||||
golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
|
||||
golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
|
||||
golang.org/x/term v0.12.0/go.mod h1:owVbMEjm3cBLCHdkQu9b1opXd4ETQWc3BhuQGKgXgvU=
|
||||
golang.org/x/term v0.17.0/go.mod h1:lLRBjIVuehSbZlaOtGMbcMncT+aqLLLmKrsjNrUguwk=
|
||||
golang.org/x/term v0.20.0/go.mod h1:8UkIAJTvZgivsXaD6/pH6U9ecQzZ45awqEOzuCvwpFY=
|
||||
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
|
||||
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
|
||||
golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
|
||||
golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
|
||||
golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
|
||||
golang.org/x/text v0.13.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
|
||||
golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
|
||||
golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
|
||||
golang.org/x/text v0.22.0/go.mod h1:YRoo4H8PVmsu+E3Ou7cqLVH8oXWIHVoX0jqUWALQhfY=
|
||||
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
|
||||
golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
|
||||
golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
|
||||
golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
|
||||
golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58=
|
||||
golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
|
||||
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
|
||||
|
||||
345
lib/handsum/handsum.go
Normal file
345
lib/handsum/handsum.go
Normal file
@@ -0,0 +1,345 @@
|
||||
// Copyright 2025 The Wuffs Authors.
|
||||
//
|
||||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
||||
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
||||
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
|
||||
// option. This file may not be copied, modified, or distributed
|
||||
// except according to those terms.
|
||||
//
|
||||
// SPDX-License-Identifier: Apache-2.0 OR MIT
|
||||
|
||||
// ----------------
|
||||
|
||||
// Package handsum implements the Handsum image file format.
|
||||
//
|
||||
// This is a very lossy format for very small thumbnails. Very small in terms
|
||||
// of image dimensions, up to 32×32 pixels, but also in terms of file size.
|
||||
// Every Handsum image file is exactly 48 bytes (384 bits) long. This can imply
|
||||
// using as little as 0.046875 bytes (0.375 bits) per pixel.
|
||||
//
|
||||
// Each Handsum image is essentially a scaled 16×16 pixel YCbCr 4:2:0 JPEG MCU
|
||||
// (Minimum Coded Unit; 4 Luma and 2 Chroma blocks), keeping only the 15 lowest
|
||||
// frequency DCT (Discrete Cosine Transform) coefficients. Each of the (6 × 15)
|
||||
// = 90 coefficients are encoded as one nibble (4 bits) with fixed quantization
|
||||
// factors, totalling 45 bytes. The initial 3 bytes holds a 16-bit magic
|
||||
// signature, 2-bit version number and 6-bit aspect ratio.
|
||||
//
|
||||
// As of February 2025, the latest version is Version 0. All Version 0 files
|
||||
// use the sRGB color profile.
|
||||
package handsum
|
||||
|
||||
import (
|
||||
"errors"
|
||||
"image"
|
||||
"image/color"
|
||||
"io"
|
||||
|
||||
"github.com/google/wuffs/lib/lowleveljpeg"
|
||||
|
||||
"golang.org/x/image/draw"
|
||||
)
|
||||
|
||||
// FileSize is the size (in bytes) of every Handsum image file.
|
||||
const FileSize = 48
|
||||
|
||||
// MaxDimension is the maximum (inclusive) width or height of every Handsum
|
||||
// image file.
|
||||
//
|
||||
// Every image is either (W × 32) or (32 × H) or both, for some positive W or H
|
||||
// that is no greater than 32.
|
||||
const MaxDimension = 32
|
||||
|
||||
// Magic is the byte string prefix of every Handsum image file.
|
||||
//
|
||||
// It's like how every JPEG image file starts with "\xFF\xD8".
|
||||
const Magic = "\xFE\xD7"
|
||||
|
||||
func init() {
|
||||
image.RegisterFormat("handsum", Magic, Decode, DecodeConfig)
|
||||
}
|
||||
|
||||
var (
|
||||
ErrBadArgument = errors.New("handsum: bad argument")
|
||||
ErrNotAHandsumFile = errors.New("handsum: not a handsum file")
|
||||
ErrUnsupportedFileVersion = errors.New("handsum: unsupported file version")
|
||||
)
|
||||
|
||||
// Encode writes src to w in the Handsum format.
|
||||
func Encode(w io.Writer, src image.Image) error {
|
||||
if (w == nil) || (src == nil) {
|
||||
return ErrBadArgument
|
||||
}
|
||||
srcB := src.Bounds()
|
||||
srcW, srcH := srcB.Dx(), srcB.Dy()
|
||||
if (srcW <= 0) || (srcH <= 0) {
|
||||
return ErrBadArgument
|
||||
}
|
||||
|
||||
aspectRatio := byte(0x1F)
|
||||
if srcW > srcH { // Landscape.
|
||||
a := ((int64(srcH) * 64) + int64(srcW)) / (2 * int64(srcW))
|
||||
if a <= 0 {
|
||||
a = 1
|
||||
}
|
||||
aspectRatio = byte(a-1) | 0x00
|
||||
} else if srcW < srcH { // Portrait.
|
||||
a := ((int64(srcW) * 64) + int64(srcH)) / (2 * int64(srcH))
|
||||
if a <= 0 {
|
||||
a = 1
|
||||
}
|
||||
aspectRatio = byte(a-1) | 0x20
|
||||
}
|
||||
|
||||
dst := image.NewRGBA(image.Rectangle{Max: image.Point{X: 16, Y: 16}})
|
||||
draw.BiLinear.Scale(dst, dst.Bounds(), src, src.Bounds(), draw.Src, nil)
|
||||
|
||||
dstU8s := lowleveljpeg.Array6BlockU8{}
|
||||
dstU8s.ExtractFrom(dst, 0, 0)
|
||||
|
||||
dstI16s := lowleveljpeg.Array6BlockI16{}
|
||||
dstI16s.ForwardDCTFrom(&dstU8s)
|
||||
|
||||
buf := [FileSize]byte{}
|
||||
buf[0] = Magic[0]
|
||||
buf[1] = Magic[1]
|
||||
buf[2] = aspectRatio
|
||||
|
||||
bitOffset := 3 * 8
|
||||
for i := range dstI16s {
|
||||
bitOffset = encodeBlock(&buf, bitOffset, &dstI16s[i])
|
||||
}
|
||||
|
||||
_, err := w.Write(buf[:])
|
||||
return err
|
||||
}
|
||||
|
||||
func encodeBlock(buf *[FileSize]byte, bitOffset int, b *lowleveljpeg.BlockI16) int {
|
||||
for i := 0; i < nCoeffs; i++ {
|
||||
e := uint8(0)
|
||||
if i == 0 {
|
||||
e = encodeDC(b[0])
|
||||
} else {
|
||||
e = encodeAC(b[zigzag[i]])
|
||||
}
|
||||
buf[bitOffset>>3] |= e << (bitOffset & 4)
|
||||
bitOffset += 4
|
||||
}
|
||||
|
||||
return bitOffset
|
||||
}
|
||||
|
||||
func encodeDC(value int16) uint8 {
|
||||
const w = dcBucketWidth
|
||||
|
||||
v := int32(value) + ((w * 8) + (w / 2))
|
||||
v /= w
|
||||
if v < 0x0 {
|
||||
return 0x0
|
||||
} else if v > 0xF {
|
||||
return 0xF
|
||||
}
|
||||
return uint8(v)
|
||||
}
|
||||
|
||||
func encodeAC(value int16) uint8 {
|
||||
// Dividing by 2 is an arbitrary adjustment that's not mirrored on the
|
||||
// decode side, but the results seem a little more vibrant.
|
||||
const w = acBucketWidth / 2
|
||||
|
||||
v := int32(value) + ((w * 8) + (w / 2))
|
||||
v /= w
|
||||
if v < 0x0 {
|
||||
return 0x0
|
||||
} else if v > 0xF {
|
||||
return 0xF
|
||||
}
|
||||
return uint8(v)
|
||||
}
|
||||
|
||||
// Both DC and AC coefficients are quantized into 16 buckets (4 bits), but they
|
||||
// use different bucket widths:
|
||||
//
|
||||
// Bucket DC AC
|
||||
// 0x0 -1024 -128
|
||||
// 0x1 -896 -112
|
||||
// 0x2 -768 -96
|
||||
// 0x3 -640 -80
|
||||
// ... ... ...
|
||||
// 0x7 -128 -16
|
||||
// 0x8 0 0
|
||||
// 0x9 +128 +16
|
||||
// ... ... ...
|
||||
// 0xE +768 +96
|
||||
// 0xF +896 +112
|
||||
const (
|
||||
dcBucketWidth = 128
|
||||
acBucketWidth = 16
|
||||
)
|
||||
|
||||
// DecodeConfig reads a Handsum image configuration from r.
|
||||
func DecodeConfig(r io.Reader) (image.Config, error) {
|
||||
buf := [3]byte{}
|
||||
if _, err := io.ReadFull(r, buf[:]); err != nil {
|
||||
return image.Config{}, err
|
||||
} else if (buf[0] != Magic[0]) || (buf[1] != Magic[1]) {
|
||||
return image.Config{}, ErrNotAHandsumFile
|
||||
} else if (buf[2] & 0xC0) != 0 {
|
||||
return image.Config{}, ErrUnsupportedFileVersion
|
||||
}
|
||||
|
||||
w, h := decodeWidthAndHeight(buf[2])
|
||||
return image.Config{
|
||||
ColorModel: color.RGBAModel,
|
||||
Width: w,
|
||||
Height: h,
|
||||
}, nil
|
||||
}
|
||||
|
||||
// Decode reads a Handsum image from r.
|
||||
func Decode(r io.Reader) (image.Image, error) {
|
||||
buf := [FileSize]byte{}
|
||||
if _, err := io.ReadFull(r, buf[:]); err != nil {
|
||||
return nil, err
|
||||
} else if (buf[0] != Magic[0]) || (buf[1] != Magic[1]) {
|
||||
return nil, ErrNotAHandsumFile
|
||||
} else if (buf[2] & 0xC0) != 0 {
|
||||
return nil, ErrUnsupportedFileVersion
|
||||
}
|
||||
|
||||
bitOffset := 3 * 8
|
||||
lumaQuadBlockU8 := lowleveljpeg.QuadBlockU8{}
|
||||
bitOffset = decodeBlock(lumaQuadBlockU8[0x00:], 16, &buf, bitOffset)
|
||||
bitOffset = decodeBlock(lumaQuadBlockU8[0x08:], 16, &buf, bitOffset)
|
||||
bitOffset = decodeBlock(lumaQuadBlockU8[0x80:], 16, &buf, bitOffset)
|
||||
bitOffset = decodeBlock(lumaQuadBlockU8[0x88:], 16, &buf, bitOffset)
|
||||
smoothLumaBlockSeams(&lumaQuadBlockU8)
|
||||
|
||||
cbBlockU8 := lowleveljpeg.BlockU8{}
|
||||
bitOffset = decodeBlock(cbBlockU8[:], 8, &buf, bitOffset)
|
||||
cbQuadBlockU8 := lowleveljpeg.QuadBlockU8{}
|
||||
cbQuadBlockU8.UpsampleFrom(&cbBlockU8)
|
||||
|
||||
crBlockU8 := lowleveljpeg.BlockU8{}
|
||||
bitOffset = decodeBlock(crBlockU8[:], 8, &buf, bitOffset)
|
||||
crQuadBlockU8 := lowleveljpeg.QuadBlockU8{}
|
||||
crQuadBlockU8.UpsampleFrom(&crBlockU8)
|
||||
|
||||
src := &image.YCbCr{
|
||||
Y: lumaQuadBlockU8[:],
|
||||
Cb: cbQuadBlockU8[:],
|
||||
Cr: crQuadBlockU8[:],
|
||||
YStride: 16,
|
||||
CStride: 16,
|
||||
SubsampleRatio: image.YCbCrSubsampleRatio444,
|
||||
Rect: image.Rectangle{Max: image.Point{X: 16, Y: 16}},
|
||||
}
|
||||
|
||||
dstW, dstH := decodeWidthAndHeight(buf[2])
|
||||
dst := image.NewRGBA(image.Rectangle{Max: image.Point{X: dstW, Y: dstH}})
|
||||
draw.BiLinear.Scale(dst, dst.Bounds(), src, src.Bounds(), draw.Src, nil)
|
||||
return dst, nil
|
||||
}
|
||||
|
||||
func decodeWidthAndHeight(buf2 byte) (w int, h int) {
|
||||
if (buf2 & 0x20) == 0 { // Landscape.
|
||||
w = 32
|
||||
h = 1 + int(buf2&0x1F)
|
||||
} else { // Portrait.
|
||||
w = 1 + int(buf2&0x1F)
|
||||
h = 32
|
||||
}
|
||||
return w, h
|
||||
}
|
||||
|
||||
func decodeBlock(dst []byte, stride int, src *[FileSize]byte, bitOffset int) int {
|
||||
a := lowleveljpeg.BlockI16{}
|
||||
|
||||
{
|
||||
nibble := (src[bitOffset>>3] >> (bitOffset & 4)) & 15
|
||||
a[0] = (int16(nibble) - 8) * dcBucketWidth
|
||||
bitOffset += 4
|
||||
}
|
||||
|
||||
for i := 1; i < nCoeffs; i++ {
|
||||
nibble := (src[bitOffset>>3] >> (bitOffset & 4)) & 15
|
||||
a[zigzag[i]] = (int16(nibble) - 8) * acBucketWidth
|
||||
bitOffset += 4
|
||||
}
|
||||
|
||||
b := lowleveljpeg.BlockU8{}
|
||||
b.InverseDCTFrom(&a)
|
||||
|
||||
for i := 0; i < 8; i++ {
|
||||
di := i * stride
|
||||
bi := i * 8
|
||||
copy(dst[di:di+8], b[bi:bi+8])
|
||||
}
|
||||
|
||||
return bitOffset
|
||||
}
|
||||
|
||||
const nCoeffs = 15
|
||||
|
||||
// zigzag represents JPEG's zig-zag order for visiting coefficients. Handsum
|
||||
// only uses the first (1 + 2 + 3 + 4 + 5) = 15 of JPEG's 64 coefficients.
|
||||
//
|
||||
// https://en.wikipedia.org/wiki/File:JPEG_ZigZag.svg
|
||||
var zigzag = [nCoeffs]uint8{
|
||||
0o00, 0o01, 0o10, 0o20, 0o11, 0o02, 0o03, 0o12, // 0, 1, 8, 16, 9, 2, 3, 10,
|
||||
0o21, 0o30, 0o40, 0o31, 0o22, 0o13, 0o04, // 17, 24, 32, 25, 18, 11, 4,
|
||||
}
|
||||
|
||||
func smoothLumaBlockSeams(b *lowleveljpeg.QuadBlockU8) {
|
||||
for _, pair := range smoothingPairs {
|
||||
v0 := uint32(b[pair[0]])
|
||||
v1 := uint32(b[pair[1]])
|
||||
b[pair[0]] = uint8(((3 * v0) + v1 + 2) / 4)
|
||||
b[pair[1]] = uint8(((3 * v1) + v0 + 2) / 4)
|
||||
}
|
||||
|
||||
v77 := uint32(b[0x77])
|
||||
v78 := uint32(b[0x78])
|
||||
v88 := uint32(b[0x88])
|
||||
v87 := uint32(b[0x87])
|
||||
|
||||
b[0x77] = uint8(((9 * v77) + (3 * v78) + v88 + (3 * v87) + 8) / 16)
|
||||
b[0x78] = uint8(((9 * v78) + (3 * v88) + v87 + (3 * v77) + 8) / 16)
|
||||
b[0x88] = uint8(((9 * v88) + (3 * v87) + v77 + (3 * v78) + 8) / 16)
|
||||
b[0x87] = uint8(((9 * v87) + (3 * v77) + v78 + (3 * v88) + 8) / 16)
|
||||
}
|
||||
|
||||
// smoothingPairs are the seams of the four 8×8 Luma blocks in a 16×16 MCU. The
|
||||
// central 4 pixels are handled separately.
|
||||
var smoothingPairs = [28][2]uint8{
|
||||
{0x07, 0x08},
|
||||
{0x17, 0x18},
|
||||
{0x27, 0x28},
|
||||
{0x37, 0x38},
|
||||
{0x47, 0x48},
|
||||
{0x57, 0x58},
|
||||
{0x67, 0x68},
|
||||
|
||||
{0x70, 0x80},
|
||||
{0x71, 0x81},
|
||||
{0x72, 0x82},
|
||||
{0x73, 0x83},
|
||||
{0x74, 0x84},
|
||||
{0x75, 0x85},
|
||||
{0x76, 0x86},
|
||||
|
||||
{0x79, 0x89},
|
||||
{0x7A, 0x8A},
|
||||
{0x7B, 0x8B},
|
||||
{0x7C, 0x8C},
|
||||
{0x7D, 0x8D},
|
||||
{0x7E, 0x8E},
|
||||
{0x7F, 0x8F},
|
||||
|
||||
{0x97, 0x98},
|
||||
{0xA7, 0xA8},
|
||||
{0xB7, 0xB8},
|
||||
{0xC7, 0xC8},
|
||||
{0xD7, 0xD8},
|
||||
{0xE7, 0xE8},
|
||||
{0xF7, 0xF8},
|
||||
}
|
||||
BIN
test/data/bricks-color.handsum
Normal file
BIN
test/data/bricks-color.handsum
Normal file
Binary file not shown.
BIN
test/data/mona-lisa.21x32.handsum
Normal file
BIN
test/data/mona-lisa.21x32.handsum
Normal file
Binary file not shown.
Reference in New Issue
Block a user