Image Extraction

Opening a presentation unpacks its images into temporary storage, and slide.Images() reports the ones each slide references. What you get back is a common.ImageRef describing the format and pixel size and holding a path into that temporary storage, so writing an image to disk means copying it out through tempstorage.Open rather than reading the path with os.Open.

Listing and saving

for si, slide := range ppt.Slides() {
    for i, img := range slide.Images() {
        out := fmt.Sprintf("slide%d_image%d.%s", si+1, i+1, img.Format())
        in, err := tempstorage.Open(img.Path())
        if err != nil {
            return err
        }
        defer in.Close()

        f, err := os.Create(out)
        if err != nil {
            return err
        }
        defer f.Close()

        if _, err := io.Copy(f, in); err != nil {
            return err
        }
    }
}

Format() returns the name the Go image decoder gave the format, so png, jpeg or gif, which is close enough to a file extension for the example to use it as one. Note that a part stored as .jpg still reports jpeg, because the format comes from decoding the bytes rather than from the part name. Map it yourself if the extension has to match the original.

Size() returns an image.Point with the pixel dimensions read when the file was opened. That is the image’s own resolution, not the size it is drawn at on the slide, which comes from the picture shape’s extent.

Limitations

The temporary storage disappears when the presentation is closed. defer ppt.Close() removes the extracted files, so anything you want to keep has to be copied before that runs. Holding an ImageRef past Close leaves you with a path to nothing.

slide.Images() skips images that come only from the slide layout or the master. A background or a logo that renders on every slide is not a slide image; find it in ppt.Images instead, where every image in the package appears once.

Images used on several slides are stored once and reported once per slide that references them, so a run over every slide will write the same picture out more than once unless you deduplicate on the path.

Only direct image relationships of the slide are listed. A picture that belongs to another part the slide references, a chart or an embedded object, is a relationship of that part rather than of the slide, and does not appear.

Run the example

The example opens image.pptx, prints the number of images on each slide, and writes each one out as slideN_imageM.<format> with its pixel dimensions.

git clone https://github.com/unidoc/unioffice-examples.git
cd unioffice-examples/presentation/image_extraction
go run main.go

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