Convert character from UTF-8 to ISO-8859-1 manually

Question

I have the character \"ö\". If I look in this UTF-8 table I see it has the hex value F6. If I look in the Unicode table I see that \"ö\" has the indices E

Answer 1

The pages you are using are confusing you somewhat. Neither your "UTF-8 table" or "Unicode table" are giving you the value of the code point in UTF-8. They are both simply listing the Unicode value of the characters.

In Unicode, every character ("code point") has a unique number assigned to it. The character ö is assigned the code point U+00F6, which is F6 in hexadecimal, and 246 in decimal.

UTF-8 is a representation of Unicode, using a sequence of between one and four bytes per Unicode code point. The transformation from 32-bit Unicode code points to UTF-8 byte sequences is described in that article - it is pretty simple to do, once you get used to it. Of course, computers do it all the time, but you can do it with a pencil and paper easily, and in your head with a bit of practice.

If you do that transformation, you will see that U+00F6 transforms to the UTF-8 sequence C3 B6, or 1100 0011 1011 0110 in binary, which is why that is the UTF-8 representation of ö.

The other half of your question is about ISO-8859-1. This is a character encoding commonly called "Latin-1". The numeric values of the Latin-1 encoding are the same as the first 256 code points in Unicode, thus ö is F6 in Latin-1.

Once you have converted between UTF-8 and standard Unicode code points (UTF-32), it should be trivial to get the Latin-1 encoding. However, not all UTF-8 sequences / Unicode characters have corresponding Latin-1 characters.

See the excellent article The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!) for a better understanding of character encodings and transformations between them.