diff --git a/README.md b/README.md
index f19f8ab..65efb96 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,22 @@
 # Boundary Bad Apple!!
 
 Boundary-aware Bad Apple!! animation generation
+
+## Fractal
+
+Usage:
+
+Load an image with `Images`
+
+```julia
+using Images, FileIO
+img = load("examples/frame.png")
+```
+Then generate the fractal using the pseudomandelbrot function
+
+```julia
+include("src/fractal.jl")
+mandel(img, -3-2im, 2+2im)
+```
+The coördinates specified are the bottom left and top right, respectively.
+
diff --git a/src/fractal.jl b/src/fractal.jl
index a941e3e..a6d19a5 100644
--- a/src/fractal.jl
+++ b/src/fractal.jl
@@ -12,23 +12,24 @@ function sample(m, u, v)
     end
 end
 
-function is_stable(m, z1, z2, z)
+function is_stable(m, z1, z2, c)
     iter = 1000
     x1 = real(z1)
     y1 = imag(z1)
     x2 = real(z2)
     y2 = imag(z2)
-    c = z
+    z = c
     for _ in 1:iter
-        if abs(z) > 2
+        r = abs(z)
+        if r > 4
             return false
         end
         # Sample the image at position z
         u = (real(z) - x1) / (x2 - x1)
         v = (imag(z) - y1) / (y2 - y1)
         f = sample(m, u, v)
-        if f == 0
-            z = z^2
+        if f < 0.5
+            z = z^2/8 + c
         else
             z = z^2 + c
         end
@@ -42,7 +43,7 @@ function mandel(m, z1::Complex, z2::Complex)
     for (i, x) in enumerate(range(real(z1), real(z2), width))
         for (j, y) in enumerate(range(imag(z1), imag(z2), height))
             t = greyscale(m[i,j])
-            s = is_stable(m, z1, z2, x + y * im)
+            s = !is_stable(m, z1, z2, x + y * im)
             if t > 0.5
                 if s
                     buffer[i,j] = colorant"white"