2021-08-28 11:58:37 (UTC-03:00)

Marcel Rodrigues <marcelgmr@gmail.com>

README: add clarifications regarding anti aliasing

diff --git a/README.md b/README.md
index 0f0795b..948c108 100644
--- a/README.md
+++ b/README.md
@@ -98,12 +98,18 @@ polygons = font:string(s, pt, x, y, anchor, a)
 This module performs anti aliasing by downsampling the surface in half.
 Each group of 2x2 pixels is converted into one by mixing the four colors.
 Some combinatorics is used to add mixed colors to a palette.
+A palette with N colors will be converted into one with M colors.
+```
+M = C(N+3, 4) = (N+3)! / 4! / (N-1)!
+M = N * (N+1) * (N+2) * (N+3) / 24
+```
+Note that only images with 7 or less colors can be anti-aliased.
 
 ```lua
 surf:save_ppm("surf-2x.ppm", colors)
-palette = anim.aa.get_mixed_colors(colors)
 surf = anim.aa.antialias(surf, #colors)
-surf:save_ppm("surf-aa.ppm", palette)
+colors = anim.aa.get_mixed_colors(colors)
+surf:save_ppm("surf-aa.ppm", colors)
 ```
 
 ## Reading and Writing GIF files (`anim.gif`)