Bug 151926 - Preview thumbnails should be able to have their size changed, and should be stored as an image file.
Summary: Preview thumbnails should be able to have their size changed, and should be s...
Status: RESOLVED WONTFIX
Alias: None
Product: LibreOffice
Classification: Unclassified
Component: LibreOffice (show other bugs)
Version:
(earliest affected)
unspecified
Hardware: x86 (IA32) All
: medium enhancement
Assignee: Not Assigned
URL:
Whiteboard:
Keywords: needsUXEval
Depends on:
Blocks: Start-Center
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Reported: 2022-11-06 02:43 UTC by Leneka
Modified: 2022-11-09 12:31 UTC (History)
2 users (show)

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Description Leneka 2022-11-06 02:43:26 UTC
Description:
The preview image of recent documents in LibreOffice should have a sizing option. The largest benefit for being able to make the thumbnails larger or smaller would be for people who have bad eyesight. A small image may be difficult for many users to see the preview.
However my personal stake in this is that I recently lost a file I was working on when it was accidentally permanently deleted from the computer with no back up. The only remnant of the file is the image captured in the preview. Being able to see the writing in the captured image and so being able to copy it, would go a long way towards me having to rewrite all that was lost. However the text in the thumbnail preview is so small that its little more than squiggles on the screen.
I also firmly believe that if there is a preview image, there should be a file in the program files with the thumbnail image in a format that could be opened like a regular image file. A .png.

Actual Results:
na

Expected Results:
Being able to resize thumbnails, being able to open thumbnails as picture files


Reproducible: Always


User Profile Reset: No

Additional Info:
na
Comment 1 V Stuart Foote 2022-11-06 21:38:35 UTC
The Thumbnail rendering of the Most Recently Used file history shown in the Start Center are PNG previews recorded to user profile when the document was last saved.  

The previews are not intended to be zoomed or to contain high fidelity rendering of the page of the document used for the thumbnail.  They are just a visual reference. Since there is no intent for high resolution there is no need to scale or zoom in tothem while the start center is visible--they're suitable to task as is.  So IMHO => WF as zoom and resize of the SC would be a lot of effort for limited function.

=-extract binary64 encoded image used for thumbnail on SC-=

But I understand your plight, and as it happens we don't use the full resolution of the PNG preview image recorded to profile--it gets scaled down a bit (depending on module and view port). So if you want to see the detail in the actual thumbnail it can be extracted from profile.

The document thumbnail is held a base64 encoded binary file in the LibreOffice user profile-- normally in %APPDATA%\LibreOffice\4, i.e. C:\Users\<yourusername>\AppData\Roaming\LibreOffice\4\user\registrymodifications.xcu

Extraction is pretty simple, and can be done locally with no network connection.

Open the .xcu file in a text editor (gvim, notepad++, even Microsoft's notepad) 

Search or scroll to locate the "Thumbnail" stanza from the HistoryInfo for document.

Copy the text between the <value> and </value> markups.

Paste as text into a new text editor file (not Writer as LO should be closed), name it "extractThumbnail.b64" or such

Open a PS or CMD prompt, to run the conversion with this: 

"certutil -decode extractThumbnail.b64 thumbnail.png"

You should get a -decode command completed successfully and have the image to review.

Open the resulting PNG image (in a web browser, or image viewer). The image will show as much detail as is available in the thumbnail--but that will vary on the type of document and the actual size of its canvas as the preview was rendered on its last save.
Comment 2 Eike Rathke 2022-11-07 13:22:37 UTC
The preview image is extracted from an ODF document's Thumbnails/thumbnail.png if present (or generated as such when saving). That thumbnail is also used by operating systems to display it in a file manager or similar context.

Citing a Note of the ODF 1.3 standard:
"
Note: Current desktops display preview images within squares of up to 256 pixel width and height, and 24 bit per pixel. While this specification does not define upper or lower limits for preview image sizes, producers should only use image sizes that are displayed with a reasonable quality if scaled to fit into 256x256 pixel square.
"
https://docs.oasis-open.org/office/OpenDocument/v1.3/os/part2-packages/OpenDocument-v1.3-os-part2-packages.html#__RefHeading__752823_826425813
Comment 3 Heiko Tietze 2022-11-09 12:31:32 UTC
Following Stuart's WF and Eike's explanation for the size to resolve the request as WF.