Changes between Initial Version and Version 1 of img2twit Tweet

Timestamp:

05/22/2009 12:43:33 AM (15 years ago)

Author:

Sam Hocevar

Comment:

bit allocation discussion

img2twit

@@ +1 @@
+A few notes and thoughts about compressing images to 140 characters for use on Twitter.
+
+The first I read about this "competition" was [http://www.flickr.com/photos/quasimondo/3518306770/in/set-72057594062596732/ here].
+
+== Bit allocation discussion ==
+
+Twitter allows for 140 characters in a message. UTF-8 is allowed.
+
+UTF-8 is restricted to the formal Unicode definition by RFC 3629. It means that the only legal UTF-8 characters range from U+0000 to U+10FFFF. The following restrictions must also be added:
+ * The high and low surrogates, used for UTF-16 encoding, restricting the Unicode range to U+0000..U+D7FF and U+E000..U+10FFFF.
+ * The 66 non-characters.
+
+The final size of this set is:
+
+{{{
+#!latex
+$(2^20 + 2^16) - 2^11 - 66 = 1111998$
+}}}
+
+The number of bits that can be encoded using 140 such characters is computed as follows:
+
+{{{
+#!latex
+$n_{bits} = floor(\dfrac{140 \log(1111998)}{\log(2)}) = 2811$
+}}}
+
+In theory, 2811 bits is therefore the maximum we can stuff into a Twitter message. However, a lot of these characters are undefined, not yet allocated or are control characters. As of Unicode 5.1 there are 100507 graphic characters, reducing the number of expressed bits to:
+
+{{{
+#!latex
+$n_{bits} = floor(\dfrac{140 \log(100507)}{\log(2)}) = 2326$
+}}}
+
+We'll go on with this value of 2326 encodable bits.
+