Encoding an Image to JPEG in Go - go

Question

I have a struct called SpriteImage which is defined like this:
type SpriteImage struct {
dimentions image.Point
lastImgPosition image.Point
sprite *image.NRGBA
}
In my flow, I first initiate a new such struct:
func NewSpriteImage(width, height int) SpriteImage {
c := color.RGBA{0xff, 0xff, 0xff, 0xff}
blankImage := imaging.New(width, height, c)
return SpriteImage{
dimentions: image.Point{X: width, Y: height},
lastImgPosition: image.Point{X: 0, Y: 0},
sprite: blankImage,
}
}
And then I add images to this SpriteImage like so:
func (s *SpriteImage) AddImage(img image.Image) error {
imgWidth := img.Bounds().Dx()
imgHeight := img.Bounds().Dy()
// Make sure new image will fit into the sprite.
if imgWidth != s.dimentions.X {
return fmt.Errorf("image width %d mismatch sprite width %d", imgWidth, s.dimentions.X)
}
spriteHeightLeft := s.dimentions.Y - s.lastImgPosition.Y
if imgHeight > spriteHeightLeft {
return fmt.Errorf("image height %d won't fit into sprite, sprite free space %d ", imgHeight, s.dimentions.Y)
}
// add image to sprite
s.sprite = imaging.Paste(s.sprite, img, s.lastImgPosition)
// update next image position within sprite
s.lastImgPosition = s.lastImgPosition.Add(image.Point{X: 0, Y: imgHeight})
return nil
}
Eventually, I want to take this SpriteImage and encode it as JPEG. But it doesn't seem to work. The native JPEG Encode function takes up an image, but I have an image.NRGBA. So I'm using github.com/disintegration/imaging lib like so:
func (s SpriteImage) GetBytes() ([]byte, error) {
var b bytes.Buffer
w := bufio.NewWriter(&b)
if s.sprite == nil {
return nil, fmt.Errorf("sprite is nil")
}
if err := imaging.Encode(w, s.sprite, imaging.JPEG); err != nil {
return nil, err
}
return b.Bytes(), nil
}
However is seems that the bytes returned are not in fact JPEG. The native Go JPEG lib will not decode those bytes to a Go image struct. If I try to decode those bytes to image like so:
m, _, err := image.Decode(reader)
if err != nil {
log.Fatal(err)
}
I'm getting err:
image: unknown format
Any ideas?

Answer 1

So, it looks like this may be an issue with the github.com/disintegration/imaging lib. I posted an issue about it in the repo's page.
If I change my GetBytes() function to this, I get valid JPEG:
func (s SpriteImage) GetBytes() ([]byte, error) {
var b bytes.Buffer
w := bufio.NewWriter(&b)
if s.sprite == nil {
return nil, fmt.Errorf("sprite is nil")
}
im := s.sprite
err := jpeg.Encode(w, im, &jpeg.Options{jpegCompression})
if err != nil {
fmt.Println(err)
}
return b.Bytes(), nil
}

Answer 2

Maybe something to check: The image: unknown format is a common error when you don't include the image/jpeg lib and specifically decode it with it:
import (
"image/jpeg"
"io"
)
...
img, err := jpeg.Decode(r)
if err != nil {
return err
}
...
Some try to use image.Decode, but you still need to include the image/jpeg lib.
I believe it works with a blind include:
import (
_ "image/jpeg"
"image"
"io"
)
...
img, err := image.Decode(r)
if err != nil {
return err
}
...