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https://issues.apache.org/jira/browse/TIKA-4856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18109474#comment-18109474
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ASF GitHub Bot commented on TIKA-4856:
--------------------------------------
dschmidt opened a new pull request, #3096:
URL: https://github.com/apache/tika/pull/3096
Getting "the thumbnail of this file" out of Tika takes format knowledge on
the client: the THUMBNAIL of a Word or Excel file is an EMF/WMF whose usable
form is the RENDERING underneath it, a PDF has no THUMBNAIL but a page
RENDERING, the THUMBNAIL of a DOCX inside a ZIP is not the ZIP's, and with
rendering enabled the picture of an embedded OLE object is a RENDERING too,
plus the request configuration that switches the renderers on.
`POST`/`PUT /unpack/thumbnail`, next to `/unpack` and `/unpack/all`, answers
with the thumbnail as JSON: the `/rmeta` metadata object of the embedded
document that is the thumbnail and the image as base64, or `204` if the
document has none.
```
{
"metadata": { "Content-Type": "image/png", "tiff:ImageWidth": "800",
"tk:embedded-resource-type": "RENDERING", ... },
"image": "iVBORw0KGgo..."
}
```
It is one forked parse in unpack mode with a fixed parse context: text
extraction off, PDF page 1 rendered at 96 dpi without OCR, EMF/WMF thumbnails
rendered (`renderOnlyEmbeddedResourceTypes: ["THUMBNAIL"]`, from #3095, so the
pictures of embedded objects are not rendered), OCR of images off, only
THUMBNAIL and RENDERING embedded documents extracted, together with their
metadata. `ThumbnailSelector` then picks, in this order, the raster THUMBNAIL
directly below the document, the rendering of a vector THUMBNAIL, or the
RENDERING of the first page. It extracts what the document carries; it does not
resize or convert. A request-supplied parser configuration wins over the fixed
one.
Verified against a server built from main plus the open thumbnail PRs: docx,
xlsx, doc, xls, ppt, pptx, odt, epub, GeoGebra, Pages, Numbers, Keynote, mp3,
m4a, flac, ogg, pdf, nef and pef all answer with the right image; a zip, a
plain jpeg and a doc without a thumbnail answer 204. Raw camera files need
their file name (`Content-Disposition`), as they are detected by extension.
Note: `embedded-limits.maxDepth` is 3 in the fixed context because of the
off-by-one in the depth limit (separate ticket); 2 would be correct once that
is fixed.
https://issues.apache.org/jira/browse/TIKA-4856
> /unpack/thumbnail: return the document thumbnail with its metadata
> ------------------------------------------------------------------
>
> Key: TIKA-4856
> URL: https://issues.apache.org/jira/browse/TIKA-4856
> Project: Tika
> Issue Type: New Feature
> Reporter: Dominik Schmidt
> Priority: Major
>
> With TIKA-4850 through TIKA-4855 every container format that carries a
> thumbnail emits it as a THUMBNAIL embedded document, the PDF parser renders
> pages as RENDERING documents, and the EMF/WMF renderer turns the vector
> thumbnails of Office documents into raster ones. Getting "the thumbnail of
> this file" out of that still takes format knowledge on the client: the
> THUMBNAIL of a Word or Excel file is an EMF/WMF whose usable form is the
> RENDERING underneath it, a PDF has no THUMBNAIL but a page RENDERING, the
> THUMBNAIL of a DOCX inside a ZIP is not the ZIP's, and with rendering enabled
> the picture of an embedded OLE object is a RENDERING too. Plus the request
> config that switches the renderers on.
> Proposal: POST /unpack/thumbnail next to /unpack and /unpack/all, multipart
> like them. It runs the usual forked parse in unpack mode with a fixed parse
> context (PDF page 1 rendered, EMF/WMF rendered) and picks, in this order: the
> raster THUMBNAIL at depth 1; the rendering of that thumbnail; the depth-1
> RENDERING of PDF page 1. The endpoint extracts what the document carries; it
> does not resize, convert or generate previews.
> The response is JSON: the /rmeta metadata object of the selected embedded
> document, and the image as base64. Thumbnails are small, so the encoding
> overhead does not matter, and the caller gets type, dimensions, origin
> (stored thumbnail or rendering, tk:rendering:rendered-by) and path in one
> round trip without unpacking a zip. 204 when the document has no thumbnail.
> {
> "metadata": {
> "Content-Type": "image/png",
> "Content-Length": "8459",
> "tiff:ImageWidth": "800",
> "tiff:ImageLength": "1131",
> "tk:embedded-resource-type": "RENDERING",
> "tk:embedded-resource-path": "/thumbnail.emf/thumbnail.png",
> "tk:embedded-depth": "2",
> "tk:rendering:rendered-by": "poi-metafile-renderer",
> "tk:resource-name": "thumbnail.png"
> },
> "image": "iVBORw0KGgoAAAANSUhEUgAA..."
> }
> To keep the selection rule short, the metafile renderer could give the
> rendering of a THUMBNAIL the THUMBNAIL type as well (its
> tk:rendering:rendered-by tells it apart), so a raster thumbnail is a
> THUMBNAIL regardless of whether the document stored it as PNG or as EMF.
> What do you think?
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