mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 17:27:08 +08:00
257 lines
7.0 KiB
Go
257 lines
7.0 KiB
Go
// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package ofdgo
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import (
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"bytes"
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"compress/zlib"
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"context"
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"encoding/binary"
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"image"
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"io"
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"github.com/xiaoqidun/jbig2"
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)
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// pngBinaryProbeLimit 限制黑白检查读取的压缩数据与块头总量
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const pngBinaryProbeLimit = 4 << 20
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// pngBinaryProbe 按需读取连续的IDAT块，不复制压缩数据
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type pngBinaryProbe struct {
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ctx context.Context
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data []byte
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payload []byte
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remaining int
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}
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// editorBinaryImage 尝试纯黑白无损编码，不改变透明度，带附加信息或无体积收益时保留原图
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// 入参: ctx 取消上下文, data PNG图片数据, img 已解码像素，为nil时读取原图
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// 返回: []byte 更小的JBIG2数据，不适用时为nil, error 取消错误
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func editorBinaryImage(ctx context.Context, data []byte, img image.Image) ([]byte, error) {
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if err := ctx.Err(); err != nil {
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return nil, err
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}
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if !pngBinarySource(ctx, data) {
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return nil, ctx.Err()
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}
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if img == nil {
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if pngNonBinaryImage(ctx, data) {
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return nil, ctx.Err()
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}
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var err error
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img, _, err = image.Decode(imageInput{ReadCloser: io.NopCloser(bytes.NewReader(data)), ctx: ctx})
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if err != nil {
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return nil, ctx.Err()
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}
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}
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var output bytes.Buffer
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if err := jbig2.EncodeContext(ctx, &output, img, &jbig2.Options{MaxPageBytes: uint64(len(data))}); err != nil || output.Len() >= len(data) {
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return nil, ctx.Err()
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}
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if err := ctx.Err(); err != nil {
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return nil, err
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}
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return output.Bytes(), nil
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}
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// pngBinarySource 检查PNG是否仅含图像与透明度数据，避免转为JBIG2时丢失附加信息
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// 入参: ctx 取消上下文, data PNG编码数据
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// 返回: bool 是否无需保留附加信息
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func pngBinarySource(ctx context.Context, data []byte) bool {
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if len(data) < 33 || string(data[:8]) != "\x89PNG\r\n\x1a\n" {
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return false
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}
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for pos := 8; pos < len(data); {
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if ctx.Err() != nil {
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return false
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}
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if len(data)-pos < 12 {
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return false
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}
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length := uint64(binary.BigEndian.Uint32(data[pos:])) + 12
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if length > uint64(len(data)-pos) {
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return false
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}
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switch string(data[pos+4 : pos+8]) {
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case "IHDR", "PLTE", "IDAT", "tRNS":
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case "IEND":
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return length == 12 && pos+12 == len(data)
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default:
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return false
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}
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pos += int(length)
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}
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return false
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}
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// pngNonBinaryImage 检查PNG前部像素是否包含灰阶、彩色或透明度，仅用于排除黑白压缩
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// 入参: ctx 取消上下文, data PNG图片数据
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// 返回: bool 已发现非不透明黑白像素，无法判定时为false
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func pngNonBinaryImage(ctx context.Context, data []byte) bool {
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if len(data) < 33 || string(data[:8]) != "\x89PNG\r\n\x1a\n" || binary.BigEndian.Uint32(data[8:]) != 13 || string(data[12:16]) != "IHDR" {
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return false
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}
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header := data[16:29]
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width, height := binary.BigEndian.Uint32(header), binary.BigEndian.Uint32(header[4:])
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depth, kind := header[8], header[9]
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if width == 0 || height == 0 || (depth != 8 && depth != 16) || header[10] != 0 || header[11] != 0 || header[12] != 0 {
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return false
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}
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colors, channels := 0, 0
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switch kind {
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case 0:
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colors, channels = 1, 1
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case 2:
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colors, channels = 3, 3
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case 4:
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colors, channels = 1, 2
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case 6:
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colors, channels = 3, 4
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default:
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return false
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}
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colors *= int(depth / 8)
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channels *= int(depth / 8)
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size := uint64(width) * uint64(channels)
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if size > 256<<10 {
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return false
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}
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probe := pngBinaryProbe{ctx: ctx, data: data[33:], remaining: pngBinaryProbeLimit}
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for len(probe.data) >= 12 && string(probe.data[4:8]) != "IDAT" {
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if ctx.Err() != nil {
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return false
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}
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length := uint64(binary.BigEndian.Uint32(probe.data)) + 12
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if length > uint64(len(probe.data)) || length > uint64(probe.remaining) {
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return false
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}
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probe.data = probe.data[int(length):]
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probe.remaining -= int(length)
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}
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stream, err := zlib.NewReader(&probe)
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if err != nil {
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return false
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}
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defer stream.Close()
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row := make([]byte, int(size)+1)
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previous := make([]byte, int(size))
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rows := min(int64(height), 64, (1<<20)/int64(len(row)))
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for index := int64(0); index < rows; index++ {
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if ctx.Err() != nil {
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return false
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}
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if _, err := io.ReadFull(stream, row); err != nil || !pngBinaryProbeFilter(row[1:], previous, channels, row[0]) {
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return false
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}
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for offset := 1; offset < len(row); offset += channels {
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value := row[offset]
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if value != 0 && value != 255 {
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return true
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}
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for _, sample := range row[offset : offset+colors] {
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if sample != value {
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return true
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}
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}
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for _, sample := range row[offset+colors : offset+channels] {
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if sample != 255 {
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return true
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}
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}
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}
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copy(previous, row[1:])
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}
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return false
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}
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// Read 读取有限的IDAT数据，边界或长度无效时停止检查
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// 入参: output 读取缓冲区
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// 返回: int 读取字节数, error 读取错误
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func (p *pngBinaryProbe) Read(output []byte) (int, error) {
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if len(output) == 0 {
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return 0, nil
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}
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if err := p.ctx.Err(); err != nil {
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return 0, err
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}
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for len(p.payload) == 0 {
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if err := p.ctx.Err(); err != nil {
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return 0, err
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}
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if len(p.data) < 12 || p.remaining < 12 || string(p.data[4:8]) != "IDAT" {
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return 0, io.EOF
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}
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length := uint64(binary.BigEndian.Uint32(p.data))
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if length > uint64(len(p.data)-12) {
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return 0, io.ErrUnexpectedEOF
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}
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p.payload = p.data[8 : 8+int(length)]
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p.data = p.data[12+int(length):]
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p.remaining -= 12
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}
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if p.remaining == 0 {
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return 0, io.EOF
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}
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count := copy(output[:min(len(output), p.remaining)], p.payload)
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p.payload = p.payload[count:]
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p.remaining -= count
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return count, nil
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}
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// pngBinaryProbeFilter 还原黑白检查所需的扫描行
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// 入参: row 当前行, previous 前一行, stride 像素字节数, filter PNG过滤方式
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// 返回: bool 过滤方式有效
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func pngBinaryProbeFilter(row, previous []byte, stride int, filter byte) bool {
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if filter > 4 {
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return false
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}
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for index := range row {
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var left, upperLeft byte
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if index >= stride {
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left, upperLeft = row[index-stride], previous[index-stride]
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}
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up := previous[index]
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switch filter {
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case 1:
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row[index] += left
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case 2:
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row[index] += up
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case 3:
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row[index] += byte((uint16(left) + uint16(up)) / 2)
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case 4:
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a, b := int(up)-int(upperLeft), int(left)-int(upperLeft)
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c := a + b
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if a < 0 {
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a = -a
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}
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if b < 0 {
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b = -b
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}
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if c < 0 {
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c = -c
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}
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switch {
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case a <= b && a <= c:
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row[index] += left
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case b <= c:
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row[index] += up
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default:
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row[index] += upperLeft
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}
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}
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}
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return true
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}
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