func decodeFirstImage(local_path string) (firstImage image.Image, imageKind string, err error) {
imf, err := os.Open(local_path)
if err != nil {
return nil, "", err
}
defer imf.Close()
_, imageKind, err = image.DecodeConfig(imf)
if err != nil {
return nil, "", err
}
imf.Seek(0, 0)
switch imageKind {
case "gif":
// Decode GIF frames until we reach the first fully opaque image:
var g *gif.GIF
g, err = gif.DecodeAll(imf)
if err != nil {
return nil, "", err
}
firstFrame := g.Image[0]
g.Image = nil
g.Delay = nil
g = nil
return firstFrame, imageKind, nil
default:
firstImage, imageKind, err = image.Decode(imf)
if err != nil {
return nil, "", err
}
return
}
}
// Crops an image and outputs a new image file:
func cropImage(image_path string, left, top, right, bottom int) (tmp_output string, err error) {
cropBounds := image.Rect(left, top, right, bottom)
// Open the image for reading:
imf, err := os.Open(image_path)
if err != nil {
return "", err
}
defer imf.Close()
// Figure out what kind of image it is:
_, imageKind, err := image.DecodeConfig(imf)
if err != nil {
return "", err
}
imf.Seek(0, 0)
// Crop images:
switch imageKind {
case "gif":
// Decode all GIF frames and crop them:
// FIXME(jsd): This approach clearly does not work. An integrated decoder-encoder needs to be written
// for animated GIFs so as to preserve as much of the encoding details as possible and crop the
// transparent animation subframes over the full image.
var g *gif.GIF
g, err = gif.DecodeAll(imf)
if err != nil {
return "", err
}
// Crop all the frames:
for i, img := range g.Image {
if !cropBounds.In(img.Bounds()) {
return "", fmt.Errorf("Crop boundaries are not contained within image boundaries")
}
g.Image[i] = imaging.CloneKind(imaging.SubImageKind(img, cropBounds)).(*image.Paletted)
}
// Write the cropped images to a new GIF:
tmpf, err := TempFile(tmp_folder(), "crop-", ".gif")
if err != nil {
return "", err
}
defer tmpf.Close()
err = gif.EncodeAll(tmpf, g)
if err != nil {
return "", err
}
g.Image = nil
g.Delay = nil
g = nil
return tmpf.Name(), nil
case "jpeg":
img, err := jpeg.Decode(imf)
if err != nil {
return "", err
}
if !cropBounds.In(img.Bounds()) {
return "", fmt.Errorf("Crop boundaries are not contained within image boundaries")
}
tmpf, err := TempFile(tmp_folder(), "crop-", ".jpg")
if err != nil {
return "", err
}
defer tmpf.Close()
img = imaging.CloneKind(imaging.SubImageKind(img, cropBounds))
err = jpeg.Encode(tmpf, img, &jpeg.Options{Quality: 100})
if err != nil {
return "", err
}
return tmpf.Name(), nil
case "png":
img, err := png.Decode(imf)
if err != nil {
return "", err
}
if !cropBounds.In(img.Bounds()) {
return "", fmt.Errorf("Crop boundaries are not contained within image boundaries")
}
tmpf, err := TempFile(tmp_folder(), "crop-", ".png")
if err != nil {
return "", err
}
defer tmpf.Close()
img = imaging.SubImageKind(img, cropBounds)
err = png.Encode(tmpf, img)
if err != nil {
return "", err
}
return tmpf.Name(), nil
default:
return "", fmt.Errorf("Unrecognized image kind '%s'", imageKind)
}
}