Note that this feature works best for computer-rendered text rather than
handwriting.
The underlying technology is Tesseract.js.
PDFs
The PDF extraction supports:
PDFs with text information (e.g. a PDF created by a browser or a word
processing application), in which the text is extracted.
Scanned PDFs, and other PDFs whose text cannot be selected (such as documents
whose text was converted to outlines), in which the text is extracted through
an OCR process.
Mixed PDFs, containing both text and images with text content.
Note that OCR extraction is limited to 50 pages per PDF, pages containing
text information (not as an image) are not subject to this limitation.
Office documents
The text will be extracted from the following file formats:
Microsoft Word documents
Microsoft Excel documents
Only the raw text information, the cell structure is not maintained.
Values are extracted raw, so searching for dates will not work. The OpenDocument
alternative will actually extract the properly formatted value.
Microsoft PowerPoint documents
The OpenDocument alternatives to the previous formats (Text, Spreadsheet,
Presentation), created by editors such as LibreOffice and OpenOffice.
The OCR can be configured by going to Options → Media and
looking for the Text Extraction (OCR) section.
There are three ways to trigger the OCR:
By enabling Auto-process new files which will process only the
notes or attachments created after enabling the option, existing files
will remain unprocessed.
By pressing Start Batch Processing which will process all the existing
notes.
By manually requesting for an image or file to have its text extracted,
regardless of whether the automatic processing is enabled or not.
Minimum confidence
When extracting text from an image, there is a certain level of confidence
which indicates whether the extracted text appears relevant.
When the minimum confidence is set to a low percentage, the text extraction
can interpret symbols and drawings incorrectly resulting in garbled text.
If the extracted text for a note or an attachment quality is lower than
the minimum confidence, the OCR is disregarded.
Language management
OCR needs to be aware of the language of the content in order for it to
work correctly. The reason is that each language has its own data which
needs to be downloaded, and accents or other symbols will not be supported
by the default language.
To configure the languages that are supported by the OCR, simply go to Options → Language & Region and
adjust the Content languages.
When there are no content languages defined, the user interface Language is
used instead.
After making this change, the automatic processing or manual reprocessing
will take into consideration the new languages.
To enforce the detection in a particular language for a given note, use
the languageattribute,
similar to text content language.
For Attachments,
it's not possible to manually adjust the language.
Viewing extracted content for a single note
To access the extracted content of a note:
For File notes,
go to the Note buttons → Advanced → View OCR Text.
For Attachments (e.g. Images in Text notes),
double-click the attachment to view the details, press the […] button at
the left and select View extracted text (OCR).
This section allows:
Viewing the extracted text, which can be copied elsewhere if needed or
just to check the quality of the extraction.
If the note has not been extracted yet, pressing Process OCR will
process it in the background. If the extraction confidence is lower than
the minimum confidence, there will be a notification.
Similarly, if the minimum confidence was changed in settings, it is possible
to press the Process OCR button again to extract the text again.