ITU T.87 JPEG LS 标准和示例 .jls SOS 编码流没有转义序列 0xFF 0x00
ITU T.87 JPEG LS Standard and sample .jls SOS encoded streams have no escape sequence 0xFF 0x00
ITU T.81 规定如下：
B.1.1.2 Markers
Markers serve to identify the various structural
parts of the compressed data formats. Most markers start marker
segments containing a related group of parameters; some markers stand
alone. All markers are assigned two-byte codes: an X’FF’ byte followed
by a byte which is not equal to 0 or X’FF’ (see Table B.1). Any marker
may optionally be preceded by any number of fill bytes, which are
bytes assigned code X’FF’. NOTE – Because of this special
code-assignment structure, markers make it possible for a decoder to
parse the compressed data and locate its various parts without having
to decode other segments of image data. "
B.1.1.5 Entropy-coded data segments An entropy-coded data segment
contains the output of an entropy-coding procedure. It consists of an
integer number of bytes, whether the entropy-coding procedure used is
Huffman or arithmetic.
NOTES
(1) Making entropy-coded segments an
integer number of bytes is performed as follows: for Huffman coding,
1-bits are used, if necessary, to pad the end of the compressed data
to complete the final byte of a segment. For arithmetic coding, byte
alignment is performed in the procedure which terminates the
entropy-coded segment (see D.1.8).
(2) In order to ensure that a marker
does not occur within an entropy-coded segment, any X’FF’ byte
generated by either a Huffman or arithmetic encoder, or an X’FF’ byte
that was generated by the padding of 1-bits described in NOTE 1 above,
is followed by a “stuffed” zero byte (see D.1.6 and F.1.2.3).
并且在许多其他地方，众所周知的 Stuff_0() 函数也被命名。
不确定 ITU T.87 标准在 ITU T.81 标准指定的编码转义序列 0xFF 0x00 方面的立场：
- 标准的 ITU T.87 本身没有指定，但期望它。
在标准测试样本格式不正确的情况下，显然在编码流中没有编码转义序列 0xFF 0x00。例如 0xFF 0x7F、0xFF 0x2F 和其他序列可以在 .jsl 测试样本的编码流中找到：即“T8C0E3.JLS”。这么多年都没人看过；
- 或者，如果标准 ITU T.87 实际上覆盖了 ITU T.81 关于此编码流规则并且不允许转义序列编码；
在解码器中，当 0xFF 和 !0x00 实际使用该字节而不是在组件未完全解码时不跳过它时，我们可以制定逻辑来检测解码器错误。但是如果jls文件没有转义序列，我们遇到0xFF 0x00序列，我们应该跳过0x00字节吗？
想要对标准 ITU T.87 JPEG-LS 编码的主题进行一些澄清，以及正确的程序是什么。我们是否应该在编码流中对转义序列 0xFF 0x00 进行编码？
答案：
ITU T.87 - 附件 A - A1 点编码参数和压缩图像数据 - pass 3
Marker segments are inserted in the data stream as specified in Annex
D. In order to provide for easy detection of marker segments, a single
byte with the value X'FF' in a coded image data segment shall be
followed with the insertion of a single bit '0'. This inserted bit
shall occupy the most significant bit of the next byte. If the X'FF'
byte is followed by a single bit '1', then the decoder shall treat the
byte which follows as the second byte of a marker, and process it in
accordance with Annex C. If a '0' bit was inserted by the encoder, the
decoder shall discard the inserted bit, which does not form part of
the data stream to be decoded.
NOTE 2 – This marker segment detection
procedure differs from the one specified in CCITT Rec. T.81 | ISO/IEC
10918-1.
JPEG-LS T.87 覆盖了编码数据流的 T.81 JPEG 标准，使字节 0xFF 后跟值介于 0x00 和 0x7F（含）之间的字节。
ITU T.81 规定如下：
B.1.1.2 Markers Markers serve to identify the various structural parts of the compressed data formats. Most markers start marker segments containing a related group of parameters; some markers stand alone. All markers are assigned two-byte codes: an X’FF’ byte followed by a byte which is not equal to 0 or X’FF’ (see Table B.1). Any marker may optionally be preceded by any number of fill bytes, which are bytes assigned code X’FF’. NOTE – Because of this special code-assignment structure, markers make it possible for a decoder to parse the compressed data and locate its various parts without having to decode other segments of image data. "
B.1.1.5 Entropy-coded data segments An entropy-coded data segment contains the output of an entropy-coding procedure. It consists of an integer number of bytes, whether the entropy-coding procedure used is Huffman or arithmetic.
NOTES
(1) Making entropy-coded segments an integer number of bytes is performed as follows: for Huffman coding, 1-bits are used, if necessary, to pad the end of the compressed data to complete the final byte of a segment. For arithmetic coding, byte alignment is performed in the procedure which terminates the entropy-coded segment (see D.1.8).
(2) In order to ensure that a marker does not occur within an entropy-coded segment, any X’FF’ byte generated by either a Huffman or arithmetic encoder, or an X’FF’ byte that was generated by the padding of 1-bits described in NOTE 1 above, is followed by a “stuffed” zero byte (see D.1.6 and F.1.2.3).
并且在许多其他地方，众所周知的 Stuff_0() 函数也被命名。
不确定 ITU T.87 标准在 ITU T.81 标准指定的编码转义序列 0xFF 0x00 方面的立场：
- 标准的 ITU T.87 本身没有指定，但期望它。 在标准测试样本格式不正确的情况下，显然在编码流中没有编码转义序列 0xFF 0x00。例如 0xFF 0x7F、0xFF 0x2F 和其他序列可以在 .jsl 测试样本的编码流中找到：即“T8C0E3.JLS”。这么多年都没人看过；
- 或者，如果标准 ITU T.87 实际上覆盖了 ITU T.81 关于此编码流规则并且不允许转义序列编码；
在解码器中，当 0xFF 和 !0x00 实际使用该字节而不是在组件未完全解码时不跳过它时，我们可以制定逻辑来检测解码器错误。但是如果jls文件没有转义序列，我们遇到0xFF 0x00序列，我们应该跳过0x00字节吗？
想要对标准 ITU T.87 JPEG-LS 编码的主题进行一些澄清，以及正确的程序是什么。我们是否应该在编码流中对转义序列 0xFF 0x00 进行编码？
答案： ITU T.87 - 附件 A - A1 点编码参数和压缩图像数据 - pass 3
Marker segments are inserted in the data stream as specified in Annex D. In order to provide for easy detection of marker segments, a single byte with the value X'FF' in a coded image data segment shall be followed with the insertion of a single bit '0'. This inserted bit shall occupy the most significant bit of the next byte. If the X'FF' byte is followed by a single bit '1', then the decoder shall treat the byte which follows as the second byte of a marker, and process it in accordance with Annex C. If a '0' bit was inserted by the encoder, the decoder shall discard the inserted bit, which does not form part of the data stream to be decoded.
NOTE 2 – This marker segment detection procedure differs from the one specified in CCITT Rec. T.81 | ISO/IEC 10918-1.
JPEG-LS T.87 覆盖了编码数据流的 T.81 JPEG 标准，使字节 0xFF 后跟值介于 0x00 和 0x7F（含）之间的字节。