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
}

// Clone returns a copy of the given image.
func Clone(img image.Image) *image.NRGBA {
	srcBounds := img.Bounds()
	srcMinX := srcBounds.Min.X
	srcMinY := srcBounds.Min.Y

	dstBounds := srcBounds.Sub(srcBounds.Min)
	dstW := dstBounds.Dx()
	dstH := dstBounds.Dy()
	dst := image.NewNRGBA(dstBounds)

	switch src := img.(type) {

	case *image.NRGBA:
		rowSize := srcBounds.Dx() * 4
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				copy(dst.Pix[di:di+rowSize], src.Pix[si:si+rowSize])
			}
		})

	case *image.NRGBA64:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					dst.Pix[di+0] = src.Pix[si+0]
					dst.Pix[di+1] = src.Pix[si+2]
					dst.Pix[di+2] = src.Pix[si+4]
					dst.Pix[di+3] = src.Pix[si+6]
					di += 4
					si += 8
				}
			}
		})

	case *image.RGBA:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					a := src.Pix[si+3]
					dst.Pix[di+3] = a

					switch a {
					case 0:
						dst.Pix[di+0] = 0
						dst.Pix[di+1] = 0
						dst.Pix[di+2] = 0
					case 0xff:
						dst.Pix[di+0] = src.Pix[si+0]
						dst.Pix[di+1] = src.Pix[si+1]
						dst.Pix[di+2] = src.Pix[si+2]
					default:
						var tmp uint16
						tmp = uint16(src.Pix[si+0]) * 0xff / uint16(a)
						dst.Pix[di+0] = uint8(tmp)
						tmp = uint16(src.Pix[si+1]) * 0xff / uint16(a)
						dst.Pix[di+1] = uint8(tmp)
						tmp = uint16(src.Pix[si+2]) * 0xff / uint16(a)
						dst.Pix[di+2] = uint8(tmp)
					}

					di += 4
					si += 4
				}
			}
		})

	case *image.RGBA64:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					a := src.Pix[si+6]
					dst.Pix[di+3] = a

					switch a {
					case 0:
						dst.Pix[di+0] = 0
						dst.Pix[di+1] = 0
						dst.Pix[di+2] = 0
					case 0xff:
						dst.Pix[di+0] = src.Pix[si+0]
						dst.Pix[di+1] = src.Pix[si+2]
						dst.Pix[di+2] = src.Pix[si+4]
					default:
						var tmp uint16
						tmp = uint16(src.Pix[si+0]) * 0xff / uint16(a)
						dst.Pix[di+0] = uint8(tmp)
						tmp = uint16(src.Pix[si+2]) * 0xff / uint16(a)
						dst.Pix[di+1] = uint8(tmp)
						tmp = uint16(src.Pix[si+4]) * 0xff / uint16(a)
						dst.Pix[di+2] = uint8(tmp)
					}

					di += 4
					si += 8
				}
			}
		})

	case *image.Gray:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					c := src.Pix[si]
					dst.Pix[di+0] = c
					dst.Pix[di+1] = c
					dst.Pix[di+2] = c
					dst.Pix[di+3] = 0xff
					di += 4
					si += 1
				}
			}
		})

	case *image.Gray16:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					c := src.Pix[si]
					dst.Pix[di+0] = c
					dst.Pix[di+1] = c
					dst.Pix[di+2] = c
					dst.Pix[di+3] = 0xff
					di += 4
					si += 2
				}
			}
		})

	case *image.YCbCr:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					srcX := srcMinX + dstX
					srcY := srcMinY + dstY
					siy := src.YOffset(srcX, srcY)
					sic := src.COffset(srcX, srcY)
					r, g, b := color.YCbCrToRGB(src.Y[siy], src.Cb[sic], src.Cr[sic])
					dst.Pix[di+0] = r
					dst.Pix[di+1] = g
					dst.Pix[di+2] = b
					dst.Pix[di+3] = 0xff
					di += 4
				}
			}
		})

	case *image.Paletted:
		plen := len(src.Palette)
		pnew := make([]color.NRGBA, plen)
		for i := 0; i < plen; i++ {
			pnew[i] = color.NRGBAModel.Convert(src.Palette[i]).(color.NRGBA)
		}
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				si := src.PixOffset(srcMinX, srcMinY+dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					c := pnew[src.Pix[si]]
					dst.Pix[di+0] = c.R
					dst.Pix[di+1] = c.G
					dst.Pix[di+2] = c.B
					dst.Pix[di+3] = c.A
					di += 4
					si += 1
				}
			}
		})

	default:
		parallel(dstH, func(partStart, partEnd int) {
			for dstY := partStart; dstY < partEnd; dstY++ {
				di := dst.PixOffset(0, dstY)
				for dstX := 0; dstX < dstW; dstX++ {
					c := color.NRGBAModel.Convert(img.At(srcMinX+dstX, srcMinY+dstY)).(color.NRGBA)
					dst.Pix[di+0] = c.R
					dst.Pix[di+1] = c.G
					dst.Pix[di+2] = c.B
					dst.Pix[di+3] = c.A
					di += 4
				}
			}
		})

	}

	return dst
}

// toNRGBA converts any image type to *image.NRGBA with min-point at (0, 0).
func toNRGBA(img image.Image) *image.NRGBA {
	srcBounds := img.Bounds()
	if srcBounds.Min.X == 0 && srcBounds.Min.Y == 0 {
		if src0, ok := img.(*image.NRGBA); ok {
			return src0
		}
	}
	return Clone(img)
}