sample: extract a palette from the first input image

go.mod

@@ -5,6 +5,7 @@ go 1.16
 require (
 	github.com/disintegration/imaging v1.6.2
 	github.com/makeworld-the-better-one/dither/v2 v2.3.0
+	github.com/mccutchen/palettor v1.0.0 // indirect
 	github.com/urfave/cli/v2 v2.3.0
 	golang.org/x/image v0.0.0-20210220032944-ac19c3e999fb
 )

go.sum

@@ -7,6 +7,9 @@ github.com/disintegration/imaging v1.6.2 h1:w1LecBlG2Lnp8B3jk5zSuNqd7b4DXhcjwek1
 github.com/disintegration/imaging v1.6.2/go.mod h1:44/5580QXChDfwIclfc/PCwrr44amcmDAg8hxG0Ewe4=
 github.com/makeworld-the-better-one/dither/v2 v2.3.0 h1:s9wgm88KFZSzvZh9gL79tPayp5sDUGIku/1aJewxlB4=
 github.com/makeworld-the-better-one/dither/v2 v2.3.0/go.mod h1:VBtN8DXO7SNtyGmLiGA7IsFeKrBkQPze1/iAeM95arc=
+github.com/mccutchen/palettor v1.0.0 h1:YRNAzEZlRBnu8qP/9siuNTJiAj7VhL0dEQ1AQmu9jew=
+github.com/mccutchen/palettor v1.0.0/go.mod h1:5ZFq9YwI0o5zRpmAuEsm+0B7divaVds1dvTAznEnd6g=
+github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646/go.mod h1:jpp1/29i3P1S/RLdc7JQKbRpFeM1dOBd8T9ki5s+AY8=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/russross/blackfriday/v2 v2.0.1 h1:lPqVAte+HuHNfhJ/0LC98ESWRz8afy9tM/0RK8m9o+Q=

subcommand_helpers.go

@@ -9,6 +9,7 @@ import (
 	"image/gif"
 	"image/png"
 	"io"
+	"log"
 	"math"
 	"os"
 	"path/filepath"
@@ -17,6 +18,7 @@ import (
 
 	"github.com/disintegration/imaging"
 	"github.com/makeworld-the-better-one/dither/v2"
+	"github.com/mccutchen/palettor"
 	"github.com/urfave/cli/v2"
 	"golang.org/x/image/colornames"
 )
@@ -49,7 +51,9 @@ func parsePercentArg(arg string, maxOne bool) (float64, error) {
 
 // globalFlag returns the value of flag at the top level of the command.
 // For example, with the command:
-//     dither --threads 1 edm -s Simple2D
+//
+//	dither --threads 1 edm -s Simple2D
+//
 // "threads" is a global flag, and "s" is a flag local to the edm subcommand.
 func globalFlag(flag string, c *cli.Context) interface{} {
 	ancestor := c.Lineage()[len(c.Lineage())-1]
@@ -132,10 +136,38 @@ func rgbaToColor(s string) (color.NRGBA, error) {
 	return color.NRGBA{r, g, b, a}, nil
 }
 
+// extractInputPalette extracts a 5-color palette from the first input image
+// using palettor.
+func extractInputPalette(flag string, c *cli.Context) ([]color.Color, error) {
+	img, err := getInputImage(inputImages[0], c)
+	if err != nil {
+		return nil, fmt.Errorf("error loading image for palette extraction '%v': %w", inputImages, err)
+	}
+
+	// Resize: keep palettor.Extract fast. See the palettor CLI source:
+	// https://github.com/mccutchen/palettor/blob/3eaed180/cmd/palettor/palettor.go#L57
+	thumbnail := imaging.Resize(img, 200, 200, imaging.NearestNeighbor)
+
+	// TODO: make these settings configurable, particularly the number of colors
+	// in the palette. That means threading the argument through the CLI.
+	palette, err := palettor.Extract(5, 500, thumbnail)
+	if err != nil {
+		return nil, fmt.Errorf("error extracting image palette: %w", err)
+	}
+
+	log.Printf("Extracted palette: %v", palette.Colors())
+	return palette.Colors(), nil
+}
+
 // parseColors takes args and turns them into a color slice. All returned
 // colors are guaranteed to only be color.NRGBA.
 func parseColors(flag string, c *cli.Context) ([]color.Color, error) {
 	args := parseArgs([]string{globalFlag(flag, c).(string)}, " ")
+
+	if len(args) == 1 && args[0] == "sample" {
+		return extractInputPalette(flag, c)
+	}
+
 	colors := make([]color.Color, len(args))
 
 	for i, arg := range args {

subcommands.go

@@ -71,39 +71,6 @@ func preProcess(c *cli.Context) error {
 	runtime.GOMAXPROCS(int(c.Uint("threads")))
 
 	var err error
-	palette, err = parseColors("palette", c)
-	if err != nil {
-		return err
-	}
-	if len(palette) < 2 {
-		return errors.New("the palette must have at least two colors")
-	}
-
-	if c.String("recolor") != "" {
-		recolorPalette, err = parseColors("recolor", c)
-		if err != nil {
-			return err
-		}
-		if len(recolorPalette) != len(palette) {
-			return errors.New("recolor palette must have the same number of colors as the initial palette")
-		}
-	}
-
-	// Check if palette is grayscale and make image grayscale
-	// Or if the user forces it
-
-	grayscale = true
-	if !c.Bool("grayscale") {
-		// Grayscale isn't specified by the user
-		// So check to see if palette is grayscale
-		for _, c := range palette {
-			r, g, b, _ := c.RGBA()
-			if r != g || g != b {
-				grayscale = false
-				break
-			}
-		}
-	}
 
 	saturation, err = parsePercentArg(c.String("saturation"), false)
 	if err != nil {
@@ -138,6 +105,40 @@ func preProcess(c *cli.Context) error {
 		}
 	}
 
+	palette, err = parseColors("palette", c)
+	if err != nil {
+		return err
+	}
+	if len(palette) < 2 {
+		return errors.New("the palette must have at least two colors")
+	}
+
+	if c.String("recolor") != "" {
+		recolorPalette, err = parseColors("recolor", c)
+		if err != nil {
+			return err
+		}
+		if len(recolorPalette) != len(palette) {
+			return errors.New("recolor palette must have the same number of colors as the initial palette")
+		}
+	}
+
+	// Check if palette is grayscale and make image grayscale
+	// Or if the user forces it
+
+	grayscale = true
+	if !c.Bool("grayscale") {
+		// Grayscale isn't specified by the user
+		// So check to see if palette is grayscale
+		for _, c := range palette {
+			r, g, b, _ := c.RGBA()
+			if r != g || g != b {
+				grayscale = false
+				break
+			}
+		}
+	}
+
 	formatVal := c.String("format")
 	if formatVal != "png" && formatVal != "gif" {
 		return fmt.Errorf(unsupportedFormat, formatVal)