mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 17:27:08 +08:00
186 lines
6.4 KiB
Go
186 lines
6.4 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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"context"
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"encoding/binary"
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"fmt"
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"image"
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"image/color"
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"math/bits"
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"github.com/xiaoqidun/pdfgo"
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)
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// tiffFaxImage 组合独立解码的传真条带或瓦片，保留紧凑的一位像素存储
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type tiffFaxImage struct {
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blocks []image.Image
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bounds image.Rectangle
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width int
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height int
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across int
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}
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// decodeTIFFFax 按TIFF传真选项解码各图像块，复用PDFGo的T.4与T.6解码器
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// 入参: ctx 取消上下文，可为nil, data TIFF编码, layout 已校验的主图布局
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// 返回: image.Image 图像, error 字段、解码或取消错误
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func decodeTIFFFax(ctx context.Context, data []byte, layout tiffImageLayout) (image.Image, error) {
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if ctx == nil {
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ctx = context.Background()
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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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if layout.samples != 1 || layout.compression == 3 && layout.t4 & ^uint32(7) != 0 || layout.compression == 4 && layout.t6 & ^uint32(2) != 0 {
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return nil, fmt.Errorf("invalid TIFF fax options")
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}
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var order binary.ByteOrder = binary.LittleEndian
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if data[0] == 'M' {
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order = binary.BigEndian
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}
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offset := int(layout.offset)
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count := int(order.Uint16(data[offset:]))
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entries := make(map[uint16][]byte, count)
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for i := range count {
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entry := data[offset+2+i*12 : offset+14+i*12]
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entries[order.Uint16(entry)] = entry
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}
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value := func(tag uint16, fallback uint32) (uint32, error) {
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entry := entries[tag]
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if entry == nil {
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return fallback, nil
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}
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if order.Uint32(entry[4:]) != 1 {
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return 0, fmt.Errorf("invalid TIFF scalar field %d", tag)
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}
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return tiffPlaneValue(data, order, entry, 0)
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}
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for _, tag := range []uint16{258, 317, 339} {
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v, err := value(tag, 1)
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if err != nil || v != 1 || entries[tag] != nil && order.Uint16(entries[tag][2:]) != 3 {
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return nil, fmt.Errorf("invalid TIFF fax sample field %d", tag)
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}
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}
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photo, err := value(262, 2)
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if err != nil || photo > 1 && photo != 4 || entries[338] != nil {
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return nil, fmt.Errorf("invalid TIFF fax color model")
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}
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width := uint32(layout.width)
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height, err := value(278, ^uint32(0))
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if err != nil || height == 0 {
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return nil, fmt.Errorf("invalid TIFF rows per strip")
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}
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height = min(height, uint32(layout.height))
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locations, lengths := entries[273], entries[279]
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tiled := entries[322] != nil
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if tiled {
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width, err = value(322, 0)
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if err != nil || width == 0 || width%16 != 0 {
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return nil, fmt.Errorf("invalid TIFF tile width")
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}
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height, err = value(323, 0)
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if err != nil || height == 0 || height%16 != 0 {
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return nil, fmt.Errorf("invalid TIFF tile height")
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}
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locations, lengths = entries[324], entries[325]
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if locations != nil && order.Uint16(locations[2:]) != 4 {
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return nil, fmt.Errorf("invalid TIFF tile offsets")
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}
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}
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if uint64(width) > uint64(int(^uint(0)>>1)) || uint64(height) > uint64(int(^uint(0)>>1)) || locations == nil || lengths == nil {
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return nil, fmt.Errorf("invalid TIFF fax blocks")
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}
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across := (uint64(layout.width)-1)/uint64(width) + 1
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down := (uint64(layout.height)-1)/uint64(height) + 1
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blocks := across * down
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if blocks != uint64(order.Uint32(locations[4:])) || blocks != uint64(order.Uint32(lengths[4:])) {
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return nil, fmt.Errorf("invalid TIFF fax block count")
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}
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result := &tiffFaxImage{bounds: image.Rect(0, 0, layout.width, layout.height), width: int(width), height: int(height), across: int(across)}
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for i := uint64(0); i < blocks; i++ {
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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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at, err := tiffPlaneValue(data, order, locations, uint32(i))
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if err != nil {
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return nil, err
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}
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size, err := tiffPlaneValue(data, order, lengths, uint32(i))
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if err != nil || size == 0 || uint64(at)+uint64(size) > uint64(len(data)) {
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return nil, fmt.Errorf("truncated TIFF fax block")
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}
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encoded := data[uint64(at) : uint64(at)+uint64(size)]
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if layout.fillOrder == 2 {
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reversed := make([]byte, len(encoded))
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for start := 0; start < len(encoded); {
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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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end := start + min(32768, len(encoded)-start)
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for j := start; j < end; j++ {
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reversed[j] = bits.Reverse8(encoded[j])
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}
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start = end
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}
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encoded = reversed
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}
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rows := height
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if !tiled {
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rows = min(height, uint32(uint64(layout.height)-i*uint64(height)))
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}
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k := pdfgo.Integer(0)
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if layout.compression == 4 {
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k = -1
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} else if layout.compression == 3 && layout.t4&1 != 0 {
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k = 1
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}
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params := pdfgo.Dictionary{
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"K": k, "Columns": pdfgo.Integer(width), "Rows": pdfgo.Integer(rows),
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"EndOfBlock": pdfgo.Boolean(false), "EndOfLine": pdfgo.Boolean(layout.compression == 3),
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"EncodedByteAlign": pdfgo.Boolean(layout.compression == 2), "BlackIs1": pdfgo.Boolean(photo == 1 || photo == 4),
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}
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object := &pdfgo.Image{Width: int(width), Height: int(rows), BitsPerComponent: 1, ColorSpace: pdfgo.Name("DeviceGray"), Stream: &pdfgo.Stream{Dictionary: pdfgo.Dictionary{"Filter": pdfgo.Name("CCITTFaxDecode"), "DecodeParms": params}, Data: encoded}}
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pixels, err := object.DecodeSamplesContext(ctx)
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if err != nil {
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return nil, fmt.Errorf("TIFF fax block %d: %w", i, err)
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}
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result.blocks = append(result.blocks, pixels)
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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 result, nil
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}
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// Bounds 返回主图显示区域，不包含边缘瓦片的填充像素
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// 返回: image.Rectangle 图像区域
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func (s *tiffFaxImage) Bounds() image.Rectangle { return s.bounds }
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// ColorModel 返回二值图像使用的灰度颜色模型
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// 返回: color.Model 灰度模型
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func (s *tiffFaxImage) ColorModel() color.Model { return color.GrayModel }
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// At 读取所属条带或瓦片中的像素，区域外返回黑色
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// 入参: x 横向像素坐标, y 纵向像素坐标
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// 返回: color.Color 像素颜色
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func (s *tiffFaxImage) At(x, y int) color.Color {
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if !image.Pt(x, y).In(s.bounds) {
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return color.Gray{}
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}
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block := s.blocks[(y/s.height)*s.across+x/s.width]
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return block.At(x%s.width, y%s.height)
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}
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