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实现原理 #2

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youfuyu opened this issue Nov 9, 2018 · 1 comment

youfuyu commented Nov 9, 2018

叶老师可不可以讲解一下实现原理啊！看不懂啊，官方文档翻了半天，完全无法理解打击!!＿|￣|○

inkydragon commented Feb 26, 2019

先大概看看，知道 PNG 的文件格式。

极简的 PNG 大概分为：

签名 x1 b"\x89PNG\r\n\32\n"
数据块
1. IHDR(header chunk) x1
2. IDAT(image data chunk) xN
3. IEND(image trailer chunk) x1: b"IEND" + crc

基本数据块部分结尾都是 crc，函数名结尾带 c 的都是会把输入的数据加到 crc 的计算结果中。

能看懂这个 1x1 的 PNG 差不多就明白了。其他更大的无非是 IDAT 更大罢了。

A use for uncompressed PNGs | code monk

细节就只能看 RFC 了。

RFC 1951 - DEFLATE Compressed Data Format Specification version 1.3

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