mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 14:31:12 +08:00
355 lines
11 KiB
Go
355 lines
11 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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"context"
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"encoding/binary"
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"errors"
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"fmt"
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"image"
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"image/color"
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"io"
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)
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// tiffImageLayout 保存单页TIFF的尺寸、方向、采样及压缩参数
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type tiffImageLayout struct {
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width, height int
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orientation int
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offset, next uint32
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reduced, mask bool
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planar bool
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samples uint32
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depth uint32
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fillOrder uint32
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compression uint32
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t4, t6 uint32
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}
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// errTIFFRandomAccess 表示目录链需要回读，仅流式输入需重新打开资源
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var errTIFFRandomAccess = errors.New("TIFF directory requires random access")
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// tiffDirectoryInput 只替换解码视图中的首目录偏移，不复制或改写原始资源
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type tiffDirectoryInput struct {
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reader *bytes.Reader
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directory [4]byte
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ctx context.Context
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}
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// orientedTIFFImage 按方向映射像素坐标，复用原图数据与颜色精度
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type orientedTIFFImage struct {
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source image.Image
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tiffImageLayout
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}
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// isTIFFData 识别标准TIFF字节序与版本标识
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// 入参: data 文件头或完整编码
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// 返回: bool 是否为TIFF 6.0编码
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func isTIFFData(data []byte) bool {
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return len(data) >= 4 && (string(data[:4]) == "II\x2a\x00" || string(data[:4]) == "MM\x00\x2a")
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}
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// readTIFFLayout 选择单页TIFF的主图，允许缩略图目录并拒绝循环和多个主图
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// 入参: input 从文件头开始的输入流
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// 返回: tiffImageLayout 存储尺寸与方向, error 文件结构或方向错误
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func readTIFFLayout(input io.Reader) (tiffImageLayout, error) {
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var result tiffImageLayout
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var header [8]byte
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if _, err := io.ReadFull(input, header[:]); err != nil {
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return result, err
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}
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if !isTIFFData(header[:]) {
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return result, fmt.Errorf("invalid TIFF header")
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}
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var order binary.ByteOrder = binary.LittleEndian
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if header[0] == 'M' {
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order = binary.BigEndian
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}
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offset := int64(order.Uint32(header[4:]))
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position := int64(8)
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var seen map[uint32]bool
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for offset != 0 {
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if seen != nil && seen[uint32(offset)] {
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return result, fmt.Errorf("cyclic TIFF directory chain")
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}
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layout, end, err := readTIFFDirectory(input, order, offset, position)
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if err != nil {
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return result, err
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}
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if layout.mask {
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return result, fmt.Errorf("TIFF transparency mask directories are not supported")
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}
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if !layout.reduced || layout.next == 0 && seen == nil {
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if result.offset != 0 {
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return result, fmt.Errorf("multiple TIFF pages are not supported in OFD resources")
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}
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result = layout
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}
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if layout.next != 0 {
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if seen == nil {
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seen = make(map[uint32]bool)
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}
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seen[uint32(offset)] = true
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}
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offset, position = int64(layout.next), end
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}
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if result.offset == 0 {
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return result, fmt.Errorf("missing TIFF main image")
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}
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return result, nil
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}
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// readTIFFDirectory 读取目录中的图像布局和子文件类型，不读取像素
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// 入参: input 输入流, order 字节序, offset 目录偏移, position 当前流位置
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// 返回: tiffImageLayout 目录布局, int64 读取后的流位置, error 结构或读取错误
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func readTIFFDirectory(input io.Reader, order binary.ByteOrder, offset, position int64) (tiffImageLayout, int64, error) {
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var result tiffImageLayout
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var header [4]byte
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if offset < 8 {
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return result, position, fmt.Errorf("invalid TIFF directory offset")
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}
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if seeker, ok := input.(io.Seeker); ok {
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if _, err := seeker.Seek(offset, io.SeekStart); err != nil {
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return result, position, err
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}
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} else {
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if offset < position {
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return result, position, errTIFFRandomAccess
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}
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if _, err := io.CopyN(io.Discard, input, offset-position); err != nil {
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return result, position, err
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}
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}
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if _, err := io.ReadFull(input, header[:2]); err != nil {
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return result, position, err
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}
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count := int(order.Uint16(header[:2]))
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result.orientation, result.offset, result.samples, result.fillOrder = 1, uint32(offset), 1, 1
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result.depth = 1
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result.compression = 1
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var entry [12]byte
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var previous uint16
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var subfile, legacy uint32
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var hasSubfile bool
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for i := range count {
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if _, err := io.ReadFull(input, entry[:]); err != nil {
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return result, position, err
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}
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tag, kind, number := order.Uint16(entry[:2]), order.Uint16(entry[2:4]), order.Uint32(entry[4:8])
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if i > 0 && tag <= previous {
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return result, position, fmt.Errorf("invalid TIFF directory order")
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}
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previous = tag
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if tag == 258 && kind == 3 && number == 1 {
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result.depth = uint32(order.Uint16(entry[8:10]))
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}
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if tag != 254 && tag != 255 && tag != 256 && tag != 257 && tag != 259 && tag != 262 && tag != 266 && tag != 274 && tag != 277 && tag != 284 && tag != 292 && tag != 293 {
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continue
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}
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if number != 1 || kind != 3 && kind != 4 || (tag == 255 || tag == 259 || tag == 262 || tag == 266 || tag == 274 || tag == 277 || tag == 284) && kind != 3 || (tag == 254 || tag == 292 || tag == 293) && kind != 4 {
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return result, position, fmt.Errorf("invalid TIFF image layout")
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}
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value := uint64(order.Uint32(entry[8:12]))
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if kind == 3 {
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value = uint64(order.Uint16(entry[8:10]))
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}
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if (tag == 256 || tag == 257) && (value == 0 || value > uint64(int(^uint(0)>>1))) {
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return result, position, fmt.Errorf("invalid TIFF dimensions")
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}
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switch tag {
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case 254:
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subfile, hasSubfile = uint32(value), true
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case 255:
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legacy = uint32(value)
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case 256:
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result.width = int(value)
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case 257:
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result.height = int(value)
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case 259:
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result.compression = uint32(value)
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case 262:
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result.mask = value == 4
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case 266:
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if value != 1 && value != 2 {
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return result, position, fmt.Errorf("invalid TIFF fill order")
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}
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result.fillOrder = uint32(value)
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case 274:
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if value < 1 || value > 8 {
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return result, position, fmt.Errorf("invalid TIFF orientation")
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}
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result.orientation = int(value)
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case 277:
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if value == 0 {
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return result, position, fmt.Errorf("invalid TIFF sample count")
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}
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result.samples = uint32(value)
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case 284:
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if value != 1 && value != 2 {
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return result, position, fmt.Errorf("invalid TIFF planar configuration")
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}
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result.planar = value == 2
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case 292:
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result.t4 = uint32(value)
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case 293:
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result.t6 = uint32(value)
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}
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}
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if _, err := io.ReadFull(input, header[:4]); err != nil {
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return result, position, err
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}
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result.next = order.Uint32(header[:4])
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if hasSubfile {
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result.reduced, result.mask = subfile&1 != 0, result.mask || subfile&4 != 0
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} else {
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result.reduced = legacy == 2
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}
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if result.width == 0 || result.height == 0 {
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return result, position, fmt.Errorf("missing TIFF dimensions")
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}
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return result, offset + 6 + int64(count)*12, nil
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}
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// newTIFFDirectoryInput 创建以指定目录作为主图的只读解码视图
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// 入参: data 已校验的TIFF编码, offset 主图目录偏移
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// 返回: *tiffDirectoryInput 随机访问输入
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func newTIFFDirectoryInput(data []byte, offset uint32) *tiffDirectoryInput {
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input := &tiffDirectoryInput{reader: bytes.NewReader(data)}
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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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order.PutUint32(input.directory[:], offset)
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return input
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}
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// patch 替换读取片段中与首目录指针重叠的部分
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// 入参: data 读取结果, offset 文件偏移
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func (r *tiffDirectoryInput) patch(data []byte, offset int64) {
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for i := range r.directory {
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at := int64(4+i) - offset
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if at >= 0 && at < int64(len(data)) {
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data[at] = r.directory[i]
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}
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}
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}
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// Read 读取图像编码并覆盖首目录指针
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// 入参: data 接收缓冲
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// 返回: int 读取字节数, error 读取错误
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func (r *tiffDirectoryInput) Read(data []byte) (int, error) {
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if r.ctx != nil {
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if err := r.ctx.Err(); err != nil {
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return 0, err
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}
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}
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offset := r.reader.Size() - int64(r.reader.Len())
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n, err := r.reader.Read(data)
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r.patch(data[:n], offset)
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return n, err
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}
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// ReadAt 随机读取图像编码并覆盖首目录指针
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// 入参: data 接收缓冲, offset 文件偏移
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// 返回: int 读取字节数, error 读取错误
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func (r *tiffDirectoryInput) ReadAt(data []byte, offset int64) (int, error) {
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if r.ctx != nil {
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if err := r.ctx.Err(); err != nil {
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return 0, err
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}
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}
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n, err := r.reader.ReadAt(data, offset)
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r.patch(data[:n], offset)
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return n, err
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}
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// size 返回应用方向后的显示尺寸
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// 返回: image.Point 像素宽高
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func (l tiffImageLayout) size() image.Point {
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if l.orientation >= 5 {
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return image.Pt(l.height, l.width)
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}
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return image.Pt(l.width, l.height)
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}
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// Bounds 返回从零开始的显示区域
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// 返回: image.Rectangle 显示区域
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func (s *orientedTIFFImage) Bounds() image.Rectangle {
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return image.Rectangle{Max: s.size()}
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}
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// ColorModel 返回原始颜色模型
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// 返回: color.Model 颜色模型
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func (s *orientedTIFFImage) ColorModel() color.Model { return s.source.ColorModel() }
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// sourcePoint 将显示坐标映射为存储坐标
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// 入参: x 横向显示坐标, y 纵向显示坐标
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// 返回: image.Point 原始坐标, bool 是否位于显示区域内
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func (s *orientedTIFFImage) sourcePoint(x, y int) (image.Point, bool) {
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if !image.Pt(x, y).In(s.Bounds()) {
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return image.Point{}, false
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}
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w, h := s.width, s.height
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switch s.orientation {
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case 2:
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x = w - 1 - x
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case 3:
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x, y = w-1-x, h-1-y
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case 4:
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y = h - 1 - y
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case 5:
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x, y = y, x
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case 6:
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x, y = y, h-1-x
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case 7:
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x, y = w-1-y, h-1-x
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case 8:
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x, y = w-1-y, x
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}
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b := s.source.Bounds()
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return image.Pt(b.Min.X+x, b.Min.Y+y), true
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}
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// At 返回原图颜色，不重新采样或量化
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// 入参: x 横向显示坐标, y 纵向显示坐标
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// 返回: color.Color 像素颜色，区域外透明
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func (s *orientedTIFFImage) At(x, y int) color.Color {
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p, ok := s.sourcePoint(x, y)
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if !ok {
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return color.NRGBA64{}
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}
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return s.source.At(p.X, p.Y)
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}
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// NRGBA64At 读取非预乘十六位颜色，保留透明像素中的原始颜色
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// 入参: x 横向显示坐标, y 纵向显示坐标
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// 返回: color.NRGBA64 像素颜色
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func (s *orientedTIFFImage) NRGBA64At(x, y int) color.NRGBA64 {
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p, ok := s.sourcePoint(x, y)
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if !ok {
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return color.NRGBA64{}
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}
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return imageNRGBA64At(s.source, p.X, p.Y)
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}
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// RGBA64At 返回预乘十六位像素，保留原始颜色精度
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// 入参: x 横向显示坐标, y 纵向显示坐标
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// 返回: color.RGBA64 像素颜色
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func (s *orientedTIFFImage) RGBA64At(x, y int) color.RGBA64 {
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r, g, b, a := s.At(x, y).RGBA()
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return color.RGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: uint16(a)}
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}
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