imaging/helpers.go

// Package imaging provides basic image manipulation functions (resize, rotate, flip, crop, etc.).
// This package is based on the standard Go image package and works best along with it.
//
// Image manipulation functions provided by the package take any image type
// that implements `image.Image` interface as an input, and return a new image of
// `*image.NRGBA` type (32bit RGBA colors, not premultiplied by alpha).
package imaging

import (
	"errors"
	"image"
	"image/color"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"os"
	"path/filepath"
	"strings"

	"golang.org/x/image/bmp"
	"golang.org/x/image/tiff"
)

// Format is an image file format.
type Format int

// Image file formats.
const (
	JPEG Format = iota
	PNG
	GIF
	TIFF
	BMP
)

func (f Format) String() string {
	switch f {
	case JPEG:
		return "JPEG"
	case PNG:
		return "PNG"
	case GIF:
		return "GIF"
	case TIFF:
		return "TIFF"
	case BMP:
		return "BMP"
	default:
		return "Unsupported"
	}
}

var (
	// ErrUnsupportedFormat means the given image format (or file extension) is unsupported.
	ErrUnsupportedFormat = errors.New("imaging: unsupported image format")
)

// Decode reads an image from r.
func Decode(r io.Reader) (image.Image, error) {
	img, _, err := image.Decode(r)
	if err != nil {
		return nil, err
	}
	return toNRGBA(img), nil
}

// Open loads an image from file
func Open(filename string) (image.Image, error) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	img, err := Decode(file)
	return img, err
}

// Encode writes the image img to w in the specified format (JPEG, PNG, GIF, TIFF or BMP).
func Encode(w io.Writer, img image.Image, format Format) error {
	var err error
	switch format {
	case JPEG:
		var rgba *image.RGBA
		if nrgba, ok := img.(*image.NRGBA); ok {
			if nrgba.Opaque() {
				rgba = &image.RGBA{
					Pix:    nrgba.Pix,
					Stride: nrgba.Stride,
					Rect:   nrgba.Rect,
				}
			}
		}
		if rgba != nil {
			err = jpeg.Encode(w, rgba, &jpeg.Options{Quality: 95})
		} else {
			err = jpeg.Encode(w, img, &jpeg.Options{Quality: 95})
		}

	case PNG:
		err = png.Encode(w, img)
	case GIF:
		err = gif.Encode(w, img, &gif.Options{NumColors: 256})
	case TIFF:
		err = tiff.Encode(w, img, &tiff.Options{Compression: tiff.Deflate, Predictor: true})
	case BMP:
		err = bmp.Encode(w, img)
	default:
		err = ErrUnsupportedFormat
	}
	return err
}

// Save saves the image to file with the specified filename.
// The format is determined from the filename extension: "jpg" (or "jpeg"), "png", "gif", "tif" (or "tiff") and "bmp" are supported.
func Save(img image.Image, filename string) (err error) {
	formats := map[string]Format{
		".jpg":  JPEG,
		".jpeg": JPEG,
		".png":  PNG,
		".tif":  TIFF,
		".tiff": TIFF,
		".bmp":  BMP,
		".gif":  GIF,
	}

	ext := strings.ToLower(filepath.Ext(filename))
	f, ok := formats[ext]
	if !ok {
		return ErrUnsupportedFormat
	}

	file, err := os.Create(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	return Encode(file, img, f)
}

// New creates a new image with the specified width and height, and fills it with the specified color.
func New(width, height int, fillColor color.Color) *image.NRGBA {
	if width <= 0 || height <= 0 {
		return &image.NRGBA{}
	}

	dst := image.NewNRGBA(image.Rect(0, 0, width, height))
	c := color.NRGBAModel.Convert(fillColor).(color.NRGBA)

	if c.R == 0 && c.G == 0 && c.B == 0 && c.A == 0 {
		return dst
	}

	cs := []uint8{c.R, c.G, c.B, c.A}

	// fill the first row
	for x := 0; x < width; x++ {
		copy(dst.Pix[x*4:(x+1)*4], cs)
	}
	// copy the first row to other rows
	for y := 1; y < height; y++ {
		copy(dst.Pix[y*dst.Stride:y*dst.Stride+width*4], dst.Pix[0:width*4])
	}

	return dst
}