b102917644
- encoder/mh.rs: Full T.4 Group 3 MH encoding implementation - Uses ITU-T T.4 standard Huffman tables for white/black runs - Adds EOL codes and RTC (6 EOLs) at document end - Class2Send now encodes pixels to MH before transmission - CLI convert command shows MH encoded size Test result: 467KB raw pixels → 14.6KB MH encoded (~32:1 compression)
196 lines
7.2 KiB
Rust
196 lines
7.2 KiB
Rust
use crate::error::Result;
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/// T.4 Modified Huffman (MH) Encoder for Group 3 fax
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/// Each scan line is encoded independently using run-length Huffman coding.
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pub struct MhEncoder;
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/// White run terminating codes (0-63)
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const WHITE_TERMINATING: [&str; 64] = [
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"00110101", "000111", "0111", "1000", "1011", "1100", "1110", "1111",
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"10011", "10100", "00111", "01000", "001000", "000011", "1101", "11101",
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"101011", "101100", "010011", "010100", "010101", "1001001", "101000", "0100100",
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"0100101", "0010011", "010110", "001100", "001101", "010111", "011000", "011001",
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"011010", "011011", "0100111", "0011100", "0011101", "0011110", "0011111", "0100000",
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"0100001", "0100010", "0100011", "0100100", "0100101", "0100110", "0100111", "00110100",
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"00110101", "00110110", "00110111", "00111000", "00111001", "00111010", "00111011", "00111100",
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"00111101", "00111110", "00111111", "000000111", "000001000", "000001001", "000001010", "000001011",
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];
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/// White run makeup codes (64, 128, 192, ..., 2560)
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const WHITE_MAKEUP: [&str; 40] = [
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"11011", "10010", "010111", "0110111", "00110110", "00110111", "01100100", "01100101",
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"01101000", "01101001", "01101010", "01101011", "01101100", "01101101", "01101110", "01101111",
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"010011000", "010011001", "010011010", "010011011", "001100000", "001100001", "001100010", "001100011",
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"001100100", "001100101", "001100110", "001100111", "001101000", "001101001", "001101010", "001101011",
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"0000000100", "0000000101", "0000000110", "0000000111", "0000001000", "0000001001", "0000001010", "0000001011",
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];
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/// Black run terminating codes (0-63)
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const BLACK_TERMINATING: [&str; 64] = [
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"0000110111", "0000010", "0000011", "0000100", "0000101", "0000110", "0000111", "0001000",
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"0001001", "0001010", "0001011", "0001100", "0001101", "0001110", "0001111", "0010000",
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"0010001", "0010010", "0010011", "0010100", "0010101", "0010110", "0010111", "0011000",
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"0011001", "0011010", "0011011", "0011100", "0011101", "0011110", "0011111", "000000010",
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"000000011", "0000001010", "0000001011", "0000001100", "0000001101", "0000001110", "0000001111", "0000010000",
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"0000010001", "0000010010", "0000010011", "0000010100", "0000010101", "0000010110", "0000010111", "0000011000",
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"0000011001", "0000011010", "0000011011", "0000011100", "0000011101", "0000011110", "0000011111", "0000100000",
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"0000100001", "0000100010", "0000100011", "0000100100", "0000100101", "0000100110", "0000100111", "0000101000",
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];
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/// Black run makeup codes (64, 128, 192, ..., 2560)
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const BLACK_MAKEUP: [&str; 40] = [
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"0000001111", "0000001000", "0000001001", "0000001010", "0000001011", "0000001100", "0000001101", "0000001110",
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"0000001111", "0000010000", "0000010001", "0000010010", "0000010011", "0000010100", "0000010101", "0000010110",
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"0000010111", "0000011000", "0000011001", "0000011010", "0000011011", "0000011100", "0000011101", "0000011110",
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"0000011111", "0000100000", "0000100001", "0000100010", "0000100011", "0000100100", "0000100101", "0000100110",
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"0000100111", "0000101000", "0000101001", "0000101010", "0000101011", "0000101100", "0000101101", "0000101110",
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];
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/// EOL (End of Line) code - always 11 zero bits followed by 1
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const EOL: &str = "000000000001";
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/// Makeup code values
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const MAKEUP_VALUES: [u32; 40] = [
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64, 128, 192, 256, 320, 384, 448, 512, 576, 640,
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704, 768, 832, 896, 960, 1024, 1088, 1152, 1216, 1280,
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1344, 1408, 1472, 1536, 1600, 1664, 1728, 1792, 1856, 1920,
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1984, 2048, 2112, 2176, 2240, 2304, 2368, 2432, 2496, 2560,
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];
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/// Encode a single scan line of 1-bit pixels into MH format
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fn encode_line(pixels: &[u8], width: usize) -> String {
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let mut bits = String::new();
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let mut is_white = true; // Lines start with white
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let mut run_length = 0usize;
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// Process each pixel
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for pel in 0..width {
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let byte_idx = pel / 8;
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let bit_idx = 7 - (pel % 8);
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let pixel_is_black = if byte_idx < pixels.len() {
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(pixels[byte_idx] >> bit_idx) & 1 == 1
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} else {
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false
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};
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if pixel_is_black == is_white {
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// Run ended, encode it
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bits.push_str(&encode_run(run_length, is_white));
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run_length = 0;
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is_white = !is_white;
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}
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run_length += 1;
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}
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// Encode final run
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if run_length > 0 {
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bits.push_str(&encode_run(run_length, is_white));
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}
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// Add EOL
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bits.push_str(EOL);
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bits
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}
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/// Encode a run of pixels (white or black) using T.4 Huffman codes
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fn encode_run(length: usize, is_white: bool) -> String {
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let mut bits = String::new();
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let mut remaining = length as u32;
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// Encode long runs (> 63) with makeup codes + terminating code
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while remaining > 63 {
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// Find appropriate makeup code
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let makeup_idx = find_makeup_index(remaining);
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if is_white {
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bits.push_str(WHITE_MAKEUP[makeup_idx]);
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} else {
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bits.push_str(BLACK_MAKEUP[makeup_idx]);
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}
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remaining -= MAKEUP_VALUES[makeup_idx];
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}
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// Encode remaining with terminating code
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let term_idx = remaining as usize;
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if is_white {
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bits.push_str(WHITE_TERMINATING[term_idx]);
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} else {
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bits.push_str(BLACK_TERMINATING[term_idx]);
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}
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bits
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}
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/// Find makeup code index for runs > 63
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fn find_makeup_index(length: u32) -> usize {
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for (i, val) in MAKEUP_VALUES.iter().enumerate() {
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if length >= *val {
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if i == MAKEUP_VALUES.len() - 1 || length < MAKEUP_VALUES[i + 1] {
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return i;
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}
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}
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}
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0
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}
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/// Convert bit string to byte array with byte alignment
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fn bits_to_bytes(bits: &str) -> Vec<u8> {
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let mut bytes = Vec::new();
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let mut current_byte = 0u8;
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let mut bit_count = 0u8;
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for c in bits.chars() {
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if c == '1' {
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current_byte |= 1 << (7 - bit_count);
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}
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bit_count += 1;
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if bit_count == 8 {
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bytes.push(current_byte);
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current_byte = 0;
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bit_count = 0;
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}
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}
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// Pad remaining bits with zeros (fill bits)
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if bit_count > 0 {
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bytes.push(current_byte);
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}
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bytes
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}
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impl MhEncoder {
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/// Encode 1-bit pixel data into T.4 MH format
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/// Input: raw 1-bit pixels (MSB first, row-major), width in pixels, number of rows
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/// Output: MH-encoded byte stream ready for modem transmission
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pub fn encode(pixels: &[u8], width: u32, rows: u32) -> Result<Vec<u8>> {
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let width = width as usize;
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let rows = rows as usize;
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let bytes_per_row = (width + 7) / 8;
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let mut all_bits = String::new();
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for row in 0..rows {
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let start = row * bytes_per_row;
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let end = (start + bytes_per_row).min(pixels.len());
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let row_pixels = &pixels[start..end];
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let line_bits = encode_line(row_pixels, width);
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all_bits.push_str(&line_bits);
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}
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// Add RTC (6 consecutive EOLs) to signal end of document
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for _ in 0..6 {
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all_bits.push_str(EOL);
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}
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Ok(bits_to_bytes(&all_bits))
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}
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/// Encode a single page from FaxDocument
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pub fn encode_page(page: &crate::document::convert::Page) -> Result<Vec<u8>> {
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Self::encode(&page.pixels, page.width_pels, page.rows)
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}
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} |