caire/process.go

package caire

import (
	"image"
	"image/color"
	_ "image/gif"
	"image/jpeg"
	_ "image/jpeg"
	_ "image/png"
	"io"

	"github.com/pkg/errors"
	_ "golang.org/x/image/bmp"
)

// SeamCarver is an interface that Carver uses to implement the Resize function.
// It takes an image and the output as parameters and returns the resized image.
type SeamCarver interface {
	Resize(*image.NRGBA) (image.Image, error)
}

// Processor options
type Processor struct {
	SobelThreshold int
	BlurRadius     int
	NewWidth       int
	NewHeight      int
	Percentage     bool
	Square         bool
	Debug          bool
}

// Resize implement the Resize method of the Carver interface.
func Resize(s SeamCarver, img *image.NRGBA) (image.Image, error) {
	return s.Resize(img)
}

// Resize is the main entry point which takes the source image
// and encodes the new, rescaled image into the output file.
func (p *Processor) Resize(img *image.NRGBA) (image.Image, error) {
	var c = NewCarver(img.Bounds().Dx(), img.Bounds().Dy())
	var newWidth, newHeight int
	var pw, ph int

	if p.NewWidth > c.Width {
		newWidth = p.NewWidth - (p.NewWidth - (p.NewWidth - c.Width))
	} else {
		newWidth = c.Width - (c.Width - (c.Width - p.NewWidth))
	}

	if p.NewHeight > c.Height {
		newHeight = p.NewHeight - (p.NewHeight - (p.NewHeight - c.Height))
	} else {
		newHeight = c.Height - (c.Height - (c.Height - p.NewHeight))
	}

	if p.NewWidth == 0 {
		newWidth = p.NewWidth
	}
	if p.NewHeight == 0 {
		newHeight = p.NewHeight
	}
	reduce := func() {
		width, height := img.Bounds().Max.X, img.Bounds().Max.Y
		c = NewCarver(width, height)
		c.ComputeSeams(img, p)
		seams := c.FindLowestEnergySeams()
		img = c.RemoveSeam(img, seams, p.Debug)
	}
	enlarge := func() {
		width, height := img.Bounds().Max.X, img.Bounds().Max.Y
		c = NewCarver(width, height)
		c.ComputeSeams(img, p)
		seams := c.FindLowestEnergySeams()
		img = c.AddSeam(img, seams, p.Debug)
	}

	if p.Percentage || p.Square {
		// When square option is used the image will be resized to a rectangular size, based on the shortest edge.
		pw = c.Width - c.Height
		ph = c.Height - c.Width

		if p.Percentage {
			// Calculate new sizes based on provided percentage.
			pw = c.Width - int(float64(c.Width)-(float64(p.NewWidth)/100*float64(c.Width)))
			ph = c.Height - int(float64(c.Height)-(float64(p.NewHeight)/100*float64(c.Height)))

			if pw > newWidth || ph > newHeight {
				return nil, errors.New("the generated image size should be less than original image size.")
			}
		}
		// Reduce image size horizontally
		for x := 0; x < pw; x++ {
			reduce()
		}
		// Reduce image size vertically
		img = c.RotateImage90(img)
		for y := 0; y < ph; y++ {
			reduce()
		}
		img = c.RotateImage270(img)
	} else if newWidth > 0 || newHeight > 0 {
		if newWidth > 0 {
			if p.NewWidth > c.Width {
				for x := 0; x < newWidth; x++ {
					enlarge()
				}
			} else {
				for x := 0; x < newWidth; x++ {
					reduce()
				}
			}
		}
		if newHeight > 0 {
			img = c.RotateImage90(img)
			if p.NewHeight > c.Height {
				for y := 0; y < newHeight; y++ {
					enlarge()
				}
			} else {
				for y := 0; y < newHeight; y++ {
					reduce()
				}
			}
			img = c.RotateImage270(img)
		}
	}
	return img, nil
}

// Process image.
func (p *Processor) Process(r io.Reader, w io.Writer) error {
	src, _, err := image.Decode(r)
	if err != nil {
		return err
	}
	img := imgToNRGBA(src)
	res, err := Resize(p, img)
	if err != nil {
		return err
	}

	return jpeg.Encode(w, res, &jpeg.Options{Quality: 100})
}

// Converts any image type to *image.NRGBA with min-point at (0, 0).
func imgToNRGBA(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
		}
	}
	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
		for dstY := 0; dstY < dstH; dstY++ {
			di := dst.PixOffset(0, dstY)
			si := src.PixOffset(srcMinX, srcMinY+dstY)
			for dstX := 0; dstX < dstW; dstX++ {
				copy(dst.Pix[di:di+rowSize], src.Pix[si:si+rowSize])
			}
		}
	case *image.YCbCr:
		for dstY := 0; dstY < dstH; 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
			}
		}
	default:
		for dstY := 0; dstY < dstH; 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
}