ImgResizer/core/encode.go

package core

import (
	"bytes"
	"fmt"
	"image"
	"image/jpeg"
	"image/png"
	"strings"

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

// EncodeImage encodes img into buf using the given format name and returns
// the MIME type for use in data URIs.
func EncodeImage(buf *bytes.Buffer, img image.Image, format string, quality int) (mimeType string, err error) {
	switch strings.ToLower(format) {
	case "jpg", "jpeg":
		err = jpeg.Encode(buf, img, &jpeg.Options{Quality: quality})
		mimeType = "image/jpeg"
	case "png":
		err = png.Encode(buf, img)
		mimeType = "image/png"
	case "tif", "tiff":
		err = tiff.Encode(buf, img, &tiff.Options{Compression: tiff.Deflate, Predictor: true})
		mimeType = "image/tiff"
	case "webp", "bmp":
		err = fmt.Errorf("format %s is read-only — use jpg, png or tif for output", format)
	default:
		err = fmt.Errorf("unknown output format: %s", format)
	}
	return
}

// ExtToFormat normalises a file extension string to a canonical format name.
func ExtToFormat(ext string) string {
	switch strings.ToLower(ext) {
	case "jpeg":
		return "jpg"
	case "tiff":
		return "tif"
	default:
		return strings.ToLower(ext)
	}
}

// GetResampleFilter returns the imaging.ResampleFilter for the given name.
// Falls back to Lanczos for unknown names.
func GetResampleFilter(name string) ResampleFilter {
	switch strings.ToLower(name) {
	case "cubic":
		return ResampleCubic
	case "linear":
		return ResampleLinear
	case "box":
		return ResampleBox
	default:
		return ResampleLanczos
	}
}