84 lines
2.6 KiB
Rust
84 lines
2.6 KiB
Rust
use bit_vec::BitVec;
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use colors::{BitDepth, ColorType};
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use png::PngData;
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const ONE_BIT_PERMUTATIONS: [u8; 2] = [0b0000_0000, 0b1111_1111];
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const TWO_BIT_PERMUTATIONS: [u8; 5] = [
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0b0000_0000,
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0b0000_1111,
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0b0011_1100,
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0b1111_0000,
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0b1111_1111,
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];
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const FOUR_BIT_PERMUTATIONS: [u8; 11] = [
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0b0000_0000,
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0b0000_0011,
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0b0000_1100,
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0b0011_0000,
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0b1100_0000,
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0b0000_1111,
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0b0011_1100,
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0b1111_0000,
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0b0011_1111,
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0b1111_1100,
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0b1111_1111,
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];
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pub fn reduce_bit_depth_8_or_less(png: &mut PngData) -> bool {
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let mut reduced = BitVec::with_capacity(png.raw_data.len() * 8);
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let bit_depth: usize = png.ihdr_data.bit_depth.as_u8() as usize;
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let mut allowed_bits = 1;
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for line in png.scan_lines() {
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let bit_vec = BitVec::from_bytes(&line.data);
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if png.ihdr_data.color_type == ColorType::Indexed {
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for (i, bit) in bit_vec.iter().enumerate() {
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let bit_index = bit_depth - (i % bit_depth);
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if bit && bit_index > allowed_bits {
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allowed_bits = bit_index.next_power_of_two();
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if allowed_bits == bit_depth {
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// Not reducable
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return false;
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}
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}
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}
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} else {
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for byte in bit_vec.to_bytes() {
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while allowed_bits < bit_depth {
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let permutations: &[u8] = if allowed_bits == 1 {
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&ONE_BIT_PERMUTATIONS
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} else if allowed_bits == 2 {
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&TWO_BIT_PERMUTATIONS
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} else if allowed_bits == 4 {
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&FOUR_BIT_PERMUTATIONS
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} else {
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return false;
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};
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if permutations.iter().any(|perm| *perm == byte) {
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break;
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} else {
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allowed_bits <<= 1;
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}
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}
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}
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}
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}
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for line in png.scan_lines() {
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reduced.extend(BitVec::from_bytes(&[line.filter]));
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let bit_vec = BitVec::from_bytes(&line.data);
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for (i, bit) in bit_vec.iter().enumerate() {
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let bit_index = bit_depth - (i % bit_depth);
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if bit_index <= allowed_bits {
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reduced.push(bit);
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}
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}
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// Pad end of line to get 8 bits per byte
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while reduced.len() % 8 != 0 {
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reduced.push(false);
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}
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}
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png.raw_data = reduced.to_bytes();
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png.ihdr_data.bit_depth = BitDepth::from_u8(allowed_bits as u8);
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true
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}
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