README.adoc: quantify how bad agg is

README.adoc

@@ -15,14 +15,23 @@ Background
 ----------
 First, I thought something as simple would already exist.
 But there's basically only _agg_, which doesn't care about keypresses,
-and it uses an inefficient file format.
+and GIF is an inefficient file format:
+
+[options="autowidth,header",cols="<,<,<,>,>"]
+|===
+| Format | Encoding | Tool                 | Filesize | Relative size
+| WebP   | Lossless | libwebp preset 9     |   401884 | 100 %
+| GIF    | Palette  | magick               |   825280 | 205 %
+| APNG   | Lossless | apngasm + oxipng -z  |   939822 | 234 %
+| GIF    | Palette  | gifski (used by agg) |  1046027 | 260 %
+|===
 
 Second, I thought this would be reasonably doable in something other than C++.
 Meanwhile, all the good important libraries have a C API.
 
 Text rendering could still see some improvements, notably with Unicode
-box-drawing characters, and keypress parsing could learn many more sequences,
-but I've already spent enough time on this project for now.
+box-drawing characters, and keypress parsing could learn many more sequences.
+I've already spent enough time on this project for now.
 
 Packages
 --------