From a4746a3e730531f5ebec49b684d9737ccb2a4f3b Mon Sep 17 00:00:00 2001
From: "Zed A. Shaw" <zed.shaw@gmail.com>
Date: Tue, 28 Oct 2025 15:00:48 -0400
Subject: [PATCH] Added the start of a simple posterize effect.

---
 filters/posterize.go | 43 +++++++++++++++++++++++++++++++++++++++++++
 filters/upscale.go   |  2 +-
 main.go              |  5 +++--
 3 files changed, 47 insertions(+), 3 deletions(-)
 create mode 100644 filters/posterize.go

diff --git a/filters/posterize.go b/filters/posterize.go
new file mode 100644
index 0000000..98e2ecd
--- /dev/null
+++ b/filters/posterize.go
@@ -0,0 +1,43 @@
+package filters
+
+import (
+  "image"
+  "image/draw"
+  "image/color"
+  "github.com/disintegration/gift"
+)
+
+type PosterizeFilter struct {
+  Depth uint8
+}
+
+func Posterize(depth uint8) gift.Filter {
+  return PosterizeFilter{depth}
+}
+
+func (filter PosterizeFilter) Bounds(src image.Rectangle) (dst_bounds image.Rectangle) {
+  return src
+}
+
+func bin(c uint8) uint8 {
+  if c <= 64 {
+    return 0
+  } else {
+    return 255
+  }
+}
+
+func (filter PosterizeFilter) Draw(dst draw.Image, src image.Image, _ *gift.Options) {
+  bounds := src.Bounds()
+
+  for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+    for x := bounds.Min.X; x < bounds.Max.X; x++ {
+      from := src.At(x, y)
+      c := from.(color.NRGBA)
+      c.R = bin(c.R)
+      c.G = bin(c.G)
+      c.B = bin(c.B)
+      dst.Set(x, y, c)
+    }
+  }
+}
diff --git a/filters/upscale.go b/filters/upscale.go
index 4c8e878..712865f 100644
--- a/filters/upscale.go
+++ b/filters/upscale.go
@@ -12,7 +12,7 @@ type UpscaleFilter struct {
   PixelWidth int
 }
 
-func UpscaleImage(size image.Rectangle, width int) gift.Filter {
+func Upscale(size image.Rectangle, width int) gift.Filter {
   return UpscaleFilter{size, width}
 }
 
diff --git a/main.go b/main.go
index 43716f6..0a2dbc9 100644
--- a/main.go
+++ b/main.go
@@ -58,9 +58,10 @@ func main() {
   bounds := src.Bounds()
 
   resize := gift.Resize(bounds.Max.X / opts.PixelWidth, 0, gift.NearestNeighborResampling)
-  upscale := filters.UpscaleImage(bounds, opts.PixelWidth)
+  posterize := filters.Posterize(16)
+  upscale := filters.Upscale(bounds, opts.PixelWidth)
 
-  g := gift.New(resize, upscale)
+  g := gift.New(posterize, resize, upscale)
   smaller := image.NewNRGBA(g.Bounds(bounds))
   g.Draw(smaller, src)