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iiif_image.go
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iiif_image.go
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package main
import (
"errors"
"iiif"
"image"
"image/color"
"image/draw"
"os"
"path"
"strings"
"transform"
)
// Custom errors an image read/transform operation could return
var (
ErrImageDoesNotExist = errors.New("Image file does not exist")
ErrInvalidFiletype = errors.New("Invalid or unknown file type")
ErrDecodeImage = errors.New("Unable to decode image")
ErrBadImageFile = errors.New("Unable to read image")
)
// IIIFImageDecoder defines an interface for reading images in a generic way. It's
// heavily biased toward the way we've had to do our JP2 images since they're
// the more unusual use-case.
type IIIFImageDecoder interface {
DecodeImage() (image.Image, error)
GetWidth() int
GetHeight() int
GetTileWidth() int
GetTileHeight() int
GetLevels() int
SetCrop(image.Rectangle)
SetResizeWH(int, int)
}
// ImageResource wraps a decoder, IIIF ID, and the path to the image
type ImageResource struct {
Decoder IIIFImageDecoder
ID iiif.ID
FilePath string
}
// NewImageResource initializes and returns an ImageResource for the given id
// and path. If the path doesn't resolve to a valid file, or resolves to a
// file type that isn't supported, an error is returned. File type is
// determined by extension, so images will need standard extensions in order to
// work.
func NewImageResource(id iiif.ID, filepath string) (*ImageResource, error) {
var err error
// First, does the file exist?
if _, err = os.Stat(filepath); err != nil {
Logger.Infof("Image does not exist: %#v", filepath)
return nil, ErrImageDoesNotExist
}
// File exists - is its extension registered?
newDecoder, ok := ExtDecoders[strings.ToLower(path.Ext(filepath))]
if !ok {
Logger.Errorf("Image type unknown / invalid: %#v", filepath)
return nil, ErrInvalidFiletype
}
// We have a decoder for the file type - attempt to instantiate it
d, err := newDecoder(filepath)
if err != nil {
Logger.Errorf("Unable to read image %#v: %s", filepath, err)
return nil, ErrBadImageFile
}
img := &ImageResource{ID: id, Decoder: d, FilePath: filepath}
return img, nil
}
// Apply runs all image manipulation operations described by the IIIF URL, and
// returns an image.Image ready for encoding to the client
func (res *ImageResource) Apply(u *iiif.URL) (image.Image, error) {
// Crop and resize have to be prepared before we can decode
res.prep(u.Region, u.Size)
img, err := res.Decoder.DecodeImage()
if err != nil {
Logger.Errorf("Unable to decode image: %s", err)
return nil, ErrDecodeImage
}
if u.Rotation.Mirror || u.Rotation.Degrees != 0 {
img = rotate(img, u.Rotation)
}
// Unless I'm missing something, QColor doesn't actually change an image -
// e.g., if it's already color, nothing happens. If it's grayscale, there's
// nothing to do (obviously we shouldn't report it, but oh well)
switch u.Quality {
case iiif.QGray:
img = grayscale(img)
case iiif.QBitonal:
img = bitonal(img)
}
return img, nil
}
func (res *ImageResource) prep(r iiif.Region, s iiif.Size) {
w, h := res.Decoder.GetWidth(), res.Decoder.GetHeight()
crop := image.Rect(0, 0, w, h)
switch r.Type {
case iiif.RTPixel:
crop = image.Rect(int(r.X), int(r.Y), int(r.X+r.W), int(r.Y+r.H))
case iiif.RTPercent:
crop = image.Rect(
int(r.X*float64(w)/100.0),
int(r.Y*float64(h)/100.0),
int((r.X+r.W)*float64(w)/100.0),
int((r.Y+r.H)*float64(h)/100.0),
)
}
res.Decoder.SetCrop(crop)
w, h = crop.Dx(), crop.Dy()
switch s.Type {
case iiif.STScaleToWidth:
w, h = s.W, 0
case iiif.STScaleToHeight:
w, h = 0, s.H
case iiif.STExact:
w, h = s.W, s.H
case iiif.STBestFit:
w, h = res.getBestFit(w, h, s)
case iiif.STScalePercent:
w = int(float64(crop.Dx()) * s.Percent / 100.0)
h = int(float64(crop.Dy()) * s.Percent / 100.0)
}
res.Decoder.SetResizeWH(w, h)
}
// Preserving the aspect ratio, determines the proper scaling factor to get
// width and height adjusted to fit within the width and height of the desired
// size operation
func (res *ImageResource) getBestFit(width, height int, s iiif.Size) (int, int) {
fW, fH, fsW, fsH := float64(width), float64(height), float64(s.W), float64(s.H)
sf := fsW / fW
if sf*fH > fsH {
sf = fsH / fH
}
return int(sf * fW), int(sf * fH)
}
func rotate(img image.Image, rot iiif.Rotation) image.Image {
var r transform.Rotator
switch img0 := img.(type) {
case *image.Gray:
r = &transform.GrayRotator{Img: img0}
case *image.RGBA:
r = &transform.RGBARotator{Img: img0}
}
if rot.Mirror {
r.Mirror()
}
switch rot.Degrees {
case 90:
r.Rotate90()
case 180:
r.Rotate180()
case 270:
r.Rotate270()
}
return r.Image()
}
func grayscale(img image.Image) image.Image {
cm := img.ColorModel()
if cm == color.GrayModel || cm == color.Gray16Model {
return img
}
b := img.Bounds()
dst := image.NewGray(image.Rect(0, 0, b.Dx(), b.Dy()))
draw.Draw(dst, b, img, b.Min, draw.Src)
return dst
}
func bitonal(img image.Image) image.Image {
// First turn the image into 8-bit grayscale for easier manipulation
imgGray := grayscale(img).(*image.Gray)
b := imgGray.Bounds()
imgBitonal := image.NewGray(image.Rect(0, 0, b.Dx(), b.Dy()))
for i, pixel := range imgGray.Pix {
if pixel > 190 {
imgBitonal.Pix[i] = 255
}
}
return imgBitonal
}