Implement image resizing and grayscale conversion

cmd/convert.go

@@ -0,0 +1,97 @@
+/*
+Copyright © 2022 NAME HERE <EMAIL ADDRESS>
+
+*/
+package cmd
+
+import (
+	"fmt"
+	"image"
+	"image/jpeg"
+	"image/png"
+	"log"
+	"os"
+
+	"github.com/spf13/cobra"
+	"golang.org/x/image/draw"
+)
+
+// convertCmd represents the convert command
+var convertCmd = &cobra.Command{
+	Use:   "convert",
+	Short: "A brief description of your command",
+	Long: `A longer description that spans multiple lines and likely contains examples
+and usage of using your command. For example:
+
+Cobra is a CLI library for Go that empowers applications.
+This application is a tool to generate the needed files
+to quickly create a Cobra application.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		width, _ := cmd.Flags().GetInt("width")
+		height, _ := cmd.Flags().GetInt("height")
+
+		convertImage(width, height)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(convertCmd)
+
+	convertCmd.Flags().Int("width", 540, "Target width")
+	convertCmd.Flags().Int("height", 960, "Target height")
+}
+
+// Returns a new Rectangle that is resized and centered in `dst`
+func fitRectInto(src *image.Rectangle, dst *image.Rectangle) image.Rectangle {
+	var targetWidth int
+    var targetHeight int
+	var scale float64
+
+	srcRatio := float64(src.Max.X) / float64(src.Max.Y)
+	dstRatio := float64(dst.Max.X) / float64(dst.Max.Y)
+
+    if srcRatio < dstRatio {
+		// center horizontally, scale vertically
+		scale = float64(dst.Max.Y) / float64(src.Max.Y)
+	} else {
+		// center vertically, scale horizontally
+		scale = float64(dst.Max.X) / float64(src.Max.X)
+	}
+
+	targetWidth = int(float64(src.Max.X) * scale)
+	targetHeight = int(float64(src.Max.Y) * scale)
+
+	targetX := (dst.Max.X - targetWidth) / 2
+	targetY := (dst.Max.Y - targetHeight) / 2
+
+	return image.Rect(targetX, targetY, targetWidth + targetX, targetHeight + targetY)
+}
+
+func convertImage(width int, height int) {
+	// for now, we're reading a predefined input file
+	input, err := os.Open("cat.jpg")
+	if err != nil {
+		log.Fatalf("Error opening file: %v", err)
+	}
+	defer input.Close()
+
+	// … and writing to a predefined output file
+	output, err := os.OpenFile("cat_resized.png", os.O_RDWR|os.O_CREATE, 0644)
+	if err != nil {
+		log.Fatalf("Error writing output file: %v", err)
+	}
+	defer output.Close()
+
+	src, _ := jpeg.Decode(input)
+	dst := image.NewGray16(image.Rect(0, 0, width, height))
+
+	srcBounds := src.Bounds()
+	targetRect := fitRectInto(&srcBounds, &dst.Rect)
+
+	fmt.Printf("targetRect: %v", targetRect)
+
+	draw.CatmullRom.Scale(dst, targetRect, src, src.Bounds(), draw.Over, nil)
+
+	// we're taking care of a more efficient output encoding later
+	png.Encode(output, dst)
+}

cmd/root.go

@@ -27,13 +27,11 @@ import (
 // rootCmd represents the base command when called without any subcommands
 var rootCmd = &cobra.Command{
 	Use:   "inkpot-cli",
-	Short: "A brief description of your application",
-	Long: `A longer description that spans multiple lines and likely contains
-examples and usage of using your application. For example:
-
-Cobra is a CLI library for Go that empowers applications.
-This application is a tool to generate the needed files
-to quickly create a Cobra application.`,
+	Short: "Convert images for e-ink displays",
+	Long: `A command-line-tool that can be used to prepare images by
+resizing them, rotating them and converting them to 16-color
+grayscale so they can be comfortably displayed on e-ink
+displays powered by the epdiy driver.`,
 	// Uncomment the following line if your bare application
 	// has an action associated with it:
 	// Run: func(cmd *cobra.Command, args []string) { },
@@ -57,7 +55,7 @@ func init() {
 
 	// Cobra also supports local flags, which will only run
 	// when this action is called directly.
-	rootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+	// rootCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
 }
 
 

go.mod

@@ -2,4 +2,7 @@ module github.com/saunaclub/inkpot-cli
 
 go 1.16
 
-require github.com/spf13/cobra v1.3.0 // indirect
+require (
+	github.com/spf13/cobra v1.3.0
+	golang.org/x/image v0.0.0-20190802002840-cff245a6509b
+)

go.sum

@@ -358,6 +358,7 @@ golang.org/x/exp v0.0.0-20200119233911-0405dc783f0a/go.mod h1:2RIsYlXP63K8oxa1u0
 golang.org/x/exp v0.0.0-20200207192155-f17229e696bd/go.mod h1:J/WKrq2StrnmMY6+EHIKF9dgMWnmCNThgcyBT1FY9mM=
 golang.org/x/exp v0.0.0-20200224162631-6cc2880d07d6/go.mod h1:3jZMyOhIsHpP37uCMkUooju7aAi5cS1Q23tOzKc+0MU=
 golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
+golang.org/x/image v0.0.0-20190802002840-cff245a6509b h1:+qEpEAPhDZ1o0x3tHzZTQDArnOixOzGD9HUJfcg0mb4=
 golang.org/x/image v0.0.0-20190802002840-cff245a6509b/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=