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Faster bit depth check

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Kornel Lesiński 2019-01-17 16:05:00 +00:00 committed by Kornel Lesiński
parent f7337084ad
commit de61b7abf9
1 changed files with 28 additions and 17 deletions
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45
src/reduction/bit_depth.rs
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@ -78,28 +78,39 @@ pub fn reduce_bit_depth(png: &PngImage) -> Option<PngImage> {
pub fn reduce_bit_depth_8_or_less(png: &PngImage) -> Option<PngImage> {
let mut reduced = BitVec::with_capacity(png.data.len() * 8);
let bit_depth: usize = png.ihdr.bit_depth.as_u8() as usize;
let mut allowed_bits = 1;
let mut minimum_bits = 1;
if minimum_bits >= bit_depth {
return None;
}
for line in png.scan_lines() {
let bit_vec = BitVec::from_bytes(&line.data);
if png.ihdr.color_type == ColorType::Indexed {
for (i, bit) in bit_vec.iter().enumerate() {
let bit_index = bit_depth - (i % bit_depth);
if bit && bit_index > allowed_bits {
allowed_bits = bit_index.next_power_of_two();
if allowed_bits == bit_depth {
// Not reducable
return None;
}
let line_max = line.data.iter().map(|&byte| match png.ihdr.bit_depth {
BitDepth::Two => (byte & 0x3).max((byte >> 2) & 0x3).max((byte >> 4) & 0x3).max(byte >> 6),
BitDepth::Four => (byte & 0xF).max(byte >> 4),
_ => byte,
}).max().unwrap_or(0);
let required_bits = match line_max {
x if x > 0x0F => 8,
x if x > 0x03 => 4,
x if x > 0x01 => 2,
_ => 1,
};
if required_bits > minimum_bits {
minimum_bits = required_bits;
if minimum_bits >= bit_depth {
// Not reducable
return None;
}
}
} else {
let bit_vec = BitVec::from_bytes(&line.data);
for byte in bit_vec.to_bytes() {
while allowed_bits < bit_depth {
let permutations: &[u8] = if allowed_bits == 1 {
while minimum_bits < bit_depth {
let permutations: &[u8] = if minimum_bits == 1 {
&ONE_BIT_PERMUTATIONS
} else if allowed_bits == 2 {
} else if minimum_bits == 2 {
&TWO_BIT_PERMUTATIONS
} else if allowed_bits == 4 {
} else if minimum_bits == 4 {
&FOUR_BIT_PERMUTATIONS
} else {
return None;
@ -107,7 +118,7 @@ pub fn reduce_bit_depth_8_or_less(png: &PngImage) -> Option<PngImage> {
if permutations.iter().any(|perm| *perm == byte) {
break;
} else {
allowed_bits <<= 1;
minimum_bits <<= 1;
}
}
}
@ -119,7 +130,7 @@ pub fn reduce_bit_depth_8_or_less(png: &PngImage) -> Option<PngImage> {
let bit_vec = BitVec::from_bytes(&line.data);
for (i, bit) in bit_vec.iter().enumerate() {
let bit_index = bit_depth - (i % bit_depth);
if bit_index <= allowed_bits {
if bit_index <= minimum_bits {
reduced.push(bit);
}
}
@ -132,7 +143,7 @@ pub fn reduce_bit_depth_8_or_less(png: &PngImage) -> Option<PngImage> {
Some(PngImage {
data: reduced.to_bytes(),
ihdr: IhdrData {
bit_depth: BitDepth::from_u8(allowed_bits as u8),
bit_depth: BitDepth::from_u8(minimum_bits as u8),
..png.ihdr
},
aux_headers: png.aux_headers.clone(),