> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/man/man5/pbm.5.md).

# pbm.5

`pbm` — 可移植位图文件格式

## 名称

`pbm`

## 描述

可移植位图格式是一种最大公约数式的单色文件格式。它最初被设计用于在今天我们常用的那种简单网络邮件程序之间，在不同类型的机器上合理地邮寄位图。现在它作为一大类位图转换过滤器的通用语言。其定义如下：

* 用于标识文件类型的 “魔数”。pbm 文件的魔数是两个字符 “P1”。
* 空白字符（空格、TAB、CR、LF）。
* 宽度，以十进制 ASCII 字符格式表示。
* 空白字符。
* 高度，同样以十进制 ASCII 格式表示。
* 空白字符。
* 宽度 × 高度个位，每个为 ‘1’ 或 ‘0’，从位图的左上角开始，按照正常的英文阅读顺序排列。
* 字符 ‘1’ 表示黑色，‘0’ 表示白色。
* 位部分中的空白字符将被忽略。
* 从 “#” 到下一个行尾的字符将被忽略（注释）。
* 任何行都不应超过 70 个字符。

以下是此格式的一个小位图示例：

```sh
P1
# feep.pbm
24 7
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 1 1 1 0
0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 1 0
0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 1 0
0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0
0 1 0 0 0 0 0 1 1 1 1 0 0 1 1 1 1 0 0 1 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
```

读取此格式的程序应尽可能宽容，接受任何看起来稍微像位图的内容。

该格式还有一种变体，可在编译时设置 RAWBITS 选项来启用。此变体在以下方面有所不同：

* “魔数” 是 “P4” 而不是 “P1”。
* 位以每字节 8 个的方式存储，高位在前，低位在后。
* 位部分中不允许有空白字符，并且高度之后只允许单个空白字符（通常是换行符）。
* 文件小 8 倍，读写速度快许多倍。

## 作者

版权所有 (C) 1989, 1991，Jef Poskanzer。


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