How can I improve text on a yellowed/blotched page?

[j4nd3r53n]

I am working on scanning some historical texts, in Chinese - unfortunately the pages are somewhat yellowed and blotched, like the one attached. Is there a easy way to make the background paler - or even completely white - while preserving or darkening the ? I'm preparing the photo for OCR; so far I have only managed to digitalize a minor part of the text.

   

[Redraw]

(01-10-2022, 06:49 PM)j4nd3r53n Wrote: I am working on scanning some historical texts, in Chinese - unfortunately the pages are somewhat yellowed and blotched, like the one attached. Is there a easy way to make the background paler - or even completely white - while preserving or darkening the ? I'm preparing the photo for OCR; so far I have only managed to digitalize a minor part of the text.

Hello j4nd3r53n

To get this far use the Curve tool to a loose S shape try different amounts suits you best


then remove the yellow patches with the Hue Saturation tool click on yellow, reduce amount of saturation to -100  and turn up lightness to +100

might  need to redo the curve tool to increase the clarity of black print on white page.

well that's one way
also a suggestion
when scanning place a piece of black card or plastic  under  on top behind   the page to be scanned this can do wonders for removing the text on the other side that shows thru best results are with card and print same colour.


Hope this helps
Regards
Redraw

edit - looking at this again I should have increased the darkness of the black print when using the curve tool second time around um yeahup.

[denzjos]

That's what I did. G'Mic-Qt / Repair / Ian Noise Reduction 2019 (set all sliders to the right), then 'Colours / Desaturate / Mono Mixer' (use the sliders for the best result) and then 'Filters /Enhance / Sharpen (Unsharp mask)'. Then you cab use 'Colours / Curves to optimise (use a S-form curve). As Redraw mentioned, use always a black paper under the page to scan. Click on the picture for the original format. 

   

[Ofnuts]

A very simple Color ➤ Desaturate ➤ Desaturate followed by a contrast increase:

   

Side note: next time, but something dark under the page before taking a photo, this avoids the print on the other side to show through.

[j4nd3r53n]

Wow, thanks to everybody for the good answers; this really helps!