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| 1 | +# Modified from https://github.com/Fraetor/jxl_decode Original license: MIT |
| 2 | +# Added partial read support for up to 200x speedup |
| 3 | + |
| 4 | +import os |
| 5 | +from typing import List, Tuple |
| 6 | + |
| 7 | +class JXLBitstream: |
| 8 | + """ |
| 9 | + A stream of bits with methods for easy handling. |
| 10 | + """ |
| 11 | + |
| 12 | + def __init__(self, file, offset: int = 0, offsets: List[List[int]] = None): |
| 13 | + self.shift = 0 |
| 14 | + self.bitstream = bytearray() |
| 15 | + self.file = file |
| 16 | + self.offset = offset |
| 17 | + self.offsets = offsets |
| 18 | + if self.offsets: |
| 19 | + self.offset = self.offsets[0][1] |
| 20 | + self.previous_data_len = 0 |
| 21 | + self.index = 0 |
| 22 | + self.file.seek(self.offset) |
| 23 | + |
| 24 | + def get_bits(self, length: int = 1) -> int: |
| 25 | + if self.offsets and self.shift + length > self.previous_data_len + self.offsets[self.index][2]: |
| 26 | + self.partial_to_read_length = length |
| 27 | + if self.shift < self.previous_data_len + self.offsets[self.index][2]: |
| 28 | + self.partial_read(0, length) |
| 29 | + self.bitstream.extend(self.file.read(self.partial_to_read_length)) |
| 30 | + else: |
| 31 | + self.bitstream.extend(self.file.read(length)) |
| 32 | + bitmask = 2**length - 1 |
| 33 | + bits = (int.from_bytes(self.bitstream, "little") >> self.shift) & bitmask |
| 34 | + self.shift += length |
| 35 | + return bits |
| 36 | + |
| 37 | + def partial_read(self, current_length: int, length: int) -> None: |
| 38 | + self.previous_data_len += self.offsets[self.index][2] |
| 39 | + to_read_length = self.previous_data_len - (self.shift + current_length) |
| 40 | + self.bitstream.extend(self.file.read(to_read_length)) |
| 41 | + current_length += to_read_length |
| 42 | + self.partial_to_read_length -= to_read_length |
| 43 | + self.index += 1 |
| 44 | + self.file.seek(self.offsets[self.index][1]) |
| 45 | + if self.shift + length > self.previous_data_len + self.offsets[self.index][2]: |
| 46 | + self.partial_read(current_length, length) |
| 47 | + |
| 48 | + |
| 49 | +def decode_codestream(file, offset: int = 0, offsets: List[List[int]] = None) -> Tuple[int,int]: |
| 50 | + """ |
| 51 | + Decodes the actual codestream. |
| 52 | + JXL codestream specification: http://www-internal/2022/18181-1 |
| 53 | + """ |
| 54 | + |
| 55 | + # Convert codestream to int within an object to get some handy methods. |
| 56 | + codestream = JXLBitstream(file, offset=offset, offsets=offsets) |
| 57 | + |
| 58 | + # Skip signature |
| 59 | + codestream.get_bits(16) |
| 60 | + |
| 61 | + # SizeHeader |
| 62 | + div8 = codestream.get_bits(1) |
| 63 | + if div8: |
| 64 | + height = 8 * (1 + codestream.get_bits(5)) |
| 65 | + else: |
| 66 | + distribution = codestream.get_bits(2) |
| 67 | + match distribution: |
| 68 | + case 0: |
| 69 | + height = 1 + codestream.get_bits(9) |
| 70 | + case 1: |
| 71 | + height = 1 + codestream.get_bits(13) |
| 72 | + case 2: |
| 73 | + height = 1 + codestream.get_bits(18) |
| 74 | + case 3: |
| 75 | + height = 1 + codestream.get_bits(30) |
| 76 | + ratio = codestream.get_bits(3) |
| 77 | + if div8 and not ratio: |
| 78 | + width = 8 * (1 + codestream.get_bits(5)) |
| 79 | + elif not ratio: |
| 80 | + distribution = codestream.get_bits(2) |
| 81 | + match distribution: |
| 82 | + case 0: |
| 83 | + width = 1 + codestream.get_bits(9) |
| 84 | + case 1: |
| 85 | + width = 1 + codestream.get_bits(13) |
| 86 | + case 2: |
| 87 | + width = 1 + codestream.get_bits(18) |
| 88 | + case 3: |
| 89 | + width = 1 + codestream.get_bits(30) |
| 90 | + else: |
| 91 | + match ratio: |
| 92 | + case 1: |
| 93 | + width = height |
| 94 | + case 2: |
| 95 | + width = (height * 12) // 10 |
| 96 | + case 3: |
| 97 | + width = (height * 4) // 3 |
| 98 | + case 4: |
| 99 | + width = (height * 3) // 2 |
| 100 | + case 5: |
| 101 | + width = (height * 16) // 9 |
| 102 | + case 6: |
| 103 | + width = (height * 5) // 4 |
| 104 | + case 7: |
| 105 | + width = (height * 2) // 1 |
| 106 | + return width, height |
| 107 | + |
| 108 | + |
| 109 | +def decode_container(file) -> Tuple[int,int]: |
| 110 | + """ |
| 111 | + Parses the ISOBMFF container, extracts the codestream, and decodes it. |
| 112 | + JXL container specification: http://www-internal/2022/18181-2 |
| 113 | + """ |
| 114 | + |
| 115 | + def parse_box(file, file_start: int) -> dict: |
| 116 | + file.seek(file_start) |
| 117 | + LBox = int.from_bytes(file.read(4), "big") |
| 118 | + XLBox = None |
| 119 | + if 1 < LBox <= 8: |
| 120 | + raise ValueError(f"Invalid LBox at byte {file_start}.") |
| 121 | + if LBox == 1: |
| 122 | + file.seek(file_start + 8) |
| 123 | + XLBox = int.from_bytes(file.read(8), "big") |
| 124 | + if XLBox <= 16: |
| 125 | + raise ValueError(f"Invalid XLBox at byte {file_start}.") |
| 126 | + if XLBox: |
| 127 | + header_length = 16 |
| 128 | + box_length = XLBox |
| 129 | + else: |
| 130 | + header_length = 8 |
| 131 | + if LBox == 0: |
| 132 | + box_length = os.fstat(file.fileno()).st_size - file_start |
| 133 | + else: |
| 134 | + box_length = LBox |
| 135 | + file.seek(file_start + 4) |
| 136 | + box_type = file.read(4) |
| 137 | + file.seek(file_start) |
| 138 | + return { |
| 139 | + "length": box_length, |
| 140 | + "type": box_type, |
| 141 | + "offset": header_length, |
| 142 | + } |
| 143 | + |
| 144 | + file.seek(0) |
| 145 | + # Reject files missing required boxes. These two boxes are required to be at |
| 146 | + # the start and contain no values, so we can manually check there presence. |
| 147 | + # Signature box. (Redundant as has already been checked.) |
| 148 | + if file.read(12) != bytes.fromhex("0000000C 4A584C20 0D0A870A"): |
| 149 | + raise ValueError("Invalid signature box.") |
| 150 | + # File Type box. |
| 151 | + if file.read(20) != bytes.fromhex( |
| 152 | + "00000014 66747970 6A786C20 00000000 6A786C20" |
| 153 | + ): |
| 154 | + raise ValueError("Invalid file type box.") |
| 155 | + |
| 156 | + offset = 0 |
| 157 | + offsets = [] |
| 158 | + data_offset_not_found = True |
| 159 | + container_pointer = 32 |
| 160 | + file_size = os.fstat(file.fileno()).st_size |
| 161 | + while data_offset_not_found: |
| 162 | + box = parse_box(file, container_pointer) |
| 163 | + match box["type"]: |
| 164 | + case b"jxlc": |
| 165 | + offset = container_pointer + box["offset"] |
| 166 | + data_offset_not_found = False |
| 167 | + case b"jxlp": |
| 168 | + file.seek(container_pointer + box["offset"]) |
| 169 | + index = int.from_bytes(file.read(4), "big") |
| 170 | + offsets.append([index, container_pointer + box["offset"] + 4, box["length"] - box["offset"] - 4]) |
| 171 | + container_pointer += box["length"] |
| 172 | + if container_pointer >= file_size: |
| 173 | + data_offset_not_found = False |
| 174 | + |
| 175 | + if offsets: |
| 176 | + offsets.sort(key=lambda i: i[0]) |
| 177 | + file.seek(0) |
| 178 | + |
| 179 | + return decode_codestream(file, offset=offset, offsets=offsets) |
| 180 | + |
| 181 | + |
| 182 | +def get_jxl_size(path: str) -> Tuple[int,int]: |
| 183 | + with open(path, "rb") as file: |
| 184 | + if file.read(2) == bytes.fromhex("FF0A"): |
| 185 | + return decode_codestream(file) |
| 186 | + return decode_container(file) |
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