问题描述
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Please let me know if there is another Stack Exchange community this question would be better suited for.
我试图了解 Tiff 和 BigTiff 之间的基本区别.我查看了各种网站，提到的唯一区别是 BigTiff 使用 64 位偏移量，而 Tiff 使用 32 位偏移量.话虽如此，您需要知道您正在阅读这两种类型中的哪一种.这是怎么做的?根据 https://www.leadtools.com/help/Leadtools/v19/main/api/tifffmt.html，这是通过读取文件标志来完成的.但是，他们所指的标志似乎对他们自己的读者来说是独一无二的，因为我在规范中找不到相应的数据字段，如 http://www.fileformat.info/format/tiff/egff.htm.我错过了什么?BigTiff 使用的文件头是否与 Tiff 不同?
I am trying to understand the basic differences between Tiff and BigTiff. I have looked on various sites and the only difference that is mentioned is that BigTiff uses 64-bit offsets while Tiff uses 32-bit offsets. That being said, you would need to know which of the two types you are reading. How is this done? According to https://www.leadtools.com/help/leadtools/v19/main/api/tifffmt.html, this is done by reading a file flag. However, the flag they are referring to appears to be unique to their own reader as I cannot find a corresponding data field in the specifications as shown by http://www.fileformat.info/format/tiff/egff.htm. What am I missing? Does BigTiff use a different file header than Tiff?
推荐答案
BigTIFF 链接.这只是为了回答您的问题:
Everything you need to know is described in the BigTIFF link posted by @cgohlke. This is just to provide an answer to your question:
是的，它使用不同的文件头.
Yes, it uses a different file header.
普通 TIFF 使用以下标题:
Normal TIFF uses the following header:
- 2 字节字节顺序标记，II"代表Intel"/小端，或MM"代表摩托罗拉"/大端.
- (版本)编号 42* 作为 16 位值，按照给定的字节序排列.
- 对 IFD0 的无符号 32 位偏移
BigTIFF 使用稍微不同的标题:
BigTIFF uses a slightly different header:
- 2 字节字节顺序标记如上
- (版本)编号 43 作为 16 位值，按照给定的字节序排列.
- 偏移量的字节大小为 16 位值，对于 BigTIFF 始终为 8
- 2 字节填充，BigTIFF 始终为 0
- 对 IFD0 的无符号 64 位偏移
*) 选择值 42 是因为它深刻的哲学意义".或者根据官方规范，"[a]n 任意但仔细选择的数字"...
*) The value 42 was chosen for its "deep philosophical significance". Or according to the official specification, "[a]n arbitrary but carefully chosen number"...
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