Started a filters package to place my filters. First one is upscale.

filters/upscale.go

@@ -0,0 +1,39 @@
+package filters
+
+import (
+  "image"
+  "image/draw"
+  "image/color"
+  "github.com/disintegration/gift"
+)
+
+type UpscaleFilter struct {
+  Size image.Rectangle
+  PixelWidth int
+}
+
+func UpscaleImage(size image.Rectangle, width int) gift.Filter {
+  return UpscaleFilter{size, width}
+}
+
+func (filter UpscaleFilter) Bounds(src image.Rectangle) (dst_bounds image.Rectangle) {
+  return filter.Size
+}
+
+func (filter UpscaleFilter) Draw(dst draw.Image, src image.Image, _ *gift.Options) {
+  var from_x, from_y int
+  var from color.Color
+  bounds := filter.Size
+
+  for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+    for x := bounds.Min.X; x < bounds.Max.X; x++ {
+      if x % filter.PixelWidth == 0 {
+        from_x = x / filter.PixelWidth
+        from_y = y / filter.PixelWidth
+        from = src.At(from_x, from_y)
+      }
+
+      dst.Set(x, y, from)
+    }
+  }
+}

main.go

@@ -1,15 +1,13 @@
 package main
 
 import (
-  // "fmt"
   "os"
   "image"
   "log"
   "image/png"
-  "image/color"
   "github.com/disintegration/gift"
-  // "math"
   "flag"
+  "lcthw.dev/go/jankifier/filters"
 )
 
 func LoadImage(filename string) image.Image {
@@ -36,26 +34,6 @@ func SaveImage(filename string, img image.Image) {
   }
 }
 
-func UpscaleImage(bounds image.Rectangle, smaller *image.NRGBA, pixel_width int) *image.NRGBA {
-  upscale := image.NewNRGBA(bounds)
-  var from_x, from_y int
-  var from color.Color
-
-  for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
-    for x := bounds.Min.X; x < bounds.Max.X; x++ {
-      if x % pixel_width == 0 {
-        from_x = x / pixel_width
-        from_y = y / pixel_width
-        from = smaller.At(from_x, from_y)
-      }
-
-      upscale.Set(x, y, from)
-    }
-  }
-
-  return upscale
-}
-
 type Opts struct {
   InFile string
   OutFile string
@@ -80,12 +58,11 @@ func main() {
   bounds := src.Bounds()
 
   resize := gift.Resize(bounds.Max.X / opts.PixelWidth, 0, gift.NearestNeighborResampling)
+  upscale := filters.UpscaleImage(bounds, opts.PixelWidth)
 
-  g := gift.New(resize)
+  g := gift.New(resize, upscale)
   smaller := image.NewNRGBA(g.Bounds(bounds))
   g.Draw(smaller, src)
 
-  upscale := UpscaleImage(bounds, smaller, opts.PixelWidth)
-
-  SaveImage(opts.OutFile, upscale)
+  SaveImage(opts.OutFile, smaller)
 }