mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 15:06:46 +08:00
126 lines
3.9 KiB
Go
126 lines
3.9 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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"bufio"
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"encoding/binary"
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"fmt"
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"image"
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"io"
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"math/bits"
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)
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// bmpColorMask 保存一个BMP颜色分量的位域位置和取值范围
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type bmpColorMask struct {
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mask uint32
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shift uint
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max uint32
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}
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// decodeImageConfig 读取图片尺寸，BMP和TIFF只读取布局信息，不解码像素
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// 入参: input 图片输入流
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// 返回: image.Config 图片配置, string 图片格式, error 头部错误
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func decodeImageConfig(input io.Reader) (image.Config, string, error) {
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buffer := bufio.NewReader(input)
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prefix, _ := buffer.Peek(34)
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if isTIFFData(prefix) {
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layout, err := readTIFFLayout(buffer)
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if err != nil {
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return image.Config{}, "tiff", err
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}
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size := layout.displaySize()
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return image.Config{Width: size.X, Height: size.Y}, "tiff", nil
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}
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if len(prefix) == 34 && string(prefix[:2]) == "BM" {
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header := binary.LittleEndian.Uint32(prefix[14:18])
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bpp := binary.LittleEndian.Uint16(prefix[28:30])
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compression := binary.LittleEndian.Uint32(prefix[30:34])
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if (bpp == 16 || bpp == 32 && compression == 3) && (header == 40 || header == 52 || header == 56 || header == 108 || header == 124) {
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size := int(header) + 14
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if header == 40 && compression == 3 {
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size += 12
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}
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data := make([]byte, size)
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if _, err := io.ReadFull(buffer, data); err != nil {
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return image.Config{}, "bmp", err
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}
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config, err := decodeBMPConfig(data)
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return config, "bmp", err
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}
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}
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return image.DecodeConfig(buffer)
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}
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// sample 将位域采样值映射到八位通道，缺省透明度为不透明
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// 入参: value 编码像素
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// 返回: uint8 通道值
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func (m bmpColorMask) sample(value uint32) uint8 {
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if m.mask == 0 {
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return 255
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}
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return uint8(uint64((value&m.mask)>>m.shift) * 255 / uint64(m.max))
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}
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// bmpColorMasks 读取BMP真彩色通道布局，校验位域连续性、重叠及像素范围
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// 入参: data 已校验头部的BMP数据, offset 像素偏移, bpp 像素位数, compression 编码方式
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// 返回: [4]bmpColorMask 红绿蓝和透明度通道, error 格式错误
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func bmpColorMasks(data []byte, offset int, bpp uint16, compression uint32) ([4]bmpColorMask, error) {
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var result [4]bmpColorMask
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if bpp != 16 && bpp != 24 && bpp != 32 {
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return result, fmt.Errorf("unsupported bmp depth")
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}
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masks := [4]uint32{0xff0000, 0xff00, 0xff}
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if bpp == 16 {
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masks = [4]uint32{0x7c00, 0x3e0, 0x1f}
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}
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switch compression {
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case 0:
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case 3:
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if bpp == 24 {
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return result, fmt.Errorf("invalid bmp bitfield depth")
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}
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header := binary.LittleEndian.Uint32(data[14:18])
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if offset < 66 || len(data) < 66 || header != 40 && header < 52 {
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return result, fmt.Errorf("truncated bmp color masks")
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}
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for i := range 3 {
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masks[i] = binary.LittleEndian.Uint32(data[54+i*4:])
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}
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if header >= 56 {
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masks[3] = binary.LittleEndian.Uint32(data[66:70])
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}
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default:
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return result, fmt.Errorf("unsupported bmp compression")
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}
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var used uint32
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for i, mask := range masks {
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if mask == 0 {
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if i < 3 {
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return result, fmt.Errorf("empty bmp color mask")
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}
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continue
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}
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shift := uint(bits.TrailingZeros32(mask))
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maximum := mask >> shift
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if mask&used != 0 || maximum&(maximum+1) != 0 || uint64(mask)>>bpp != 0 {
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return result, fmt.Errorf("invalid bmp color mask")
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}
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result[i] = bmpColorMask{mask: mask, shift: shift, max: maximum}
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used |= mask
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}
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return result, nil
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}
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