Working with badly stained pages of text. Is it possible to select a whole page and delete a color. thus leaving
text on a white background ? These documents are from 1939-1940's and I think that the paper quality and
poor bleach is cause of stains. Unwanted color is predominantly yellow.
03-18-2019, 09:13 PM (This post was last modified: 03-18-2019, 09:24 PM by Ofnuts.)
The yellow stains aren't difficult to remove since they are of a very uniform color, which is pretty close to pure yellow. In other words, in the yellow stains the Blue channel has a very small value, instead of being identical to the Red and Green channels. So to remove the stains, we need a Blue channel which is equal to the Red or Green channels. So kick off Color>Components>Channel mixer, leve the Red and Green channels untouched, and set the Blue channel to 100% of either the Red or Green (or 50% of Red and 50% of Green).
PS: Btw, looking at the histogram, it seems the image has been heavily processed already. Can you show the original?
Herewith a unprocessed jpg image of the original page. The previous sample had been processed as I thought that if I could alter the staining to a primary colour then removal might be possible with GIMP.
03-18-2019, 10:25 PM (This post was last modified: 03-19-2019, 12:37 AM by akovia.)
(03-18-2019, 10:08 PM)TuxfordC Wrote: Herewith a unprocessed jpg image of the original page. The previous sample had been processed as I thought that if I could alter the staining to a primary colour then removal might be possible with GIMP.
Might just desaturate and adjust levels if you aren't concerned about color.
Colors > Desaturate > Desaturate (I used the Value (HSV) mode)
I didn't adjust levels as not sure what you were after but it could brighten the page considerably and darken the text, or leave it as is to show the age without the coloration. Still need some sharpening as well.
Here is you other image using the Luminance setting
Many thanks for the suggestions. Am working with them trying for an acceptable result that does not take too much
time. We are working to recover several thousand pages of an amateur radio journal for digital archiving. Some of the
printing is rough and the old paper is well stained. GIMP provides many options, too many of this novice!
Tux.
Best result are obtained by making the image monochrome, using only the Red channel: in the Channel mixer, set all three channels to 100% of the Red channel:
From that a bit of Levels, dragging both input handles inside to get full white (right handle) and full black (left handle), and using the middle handle to adjust readability:
