Problems can not remove the watermark painted with gradient

[fofwisdom]

Hello!
Vital Source recently patched the color of the watermark to be gradated.
So when I used the remover, only part of the text was erased.
I'm looking for advice if I should use the convert command multiple times.

[fofwisdom]

e6e6e6 8%, bdbdbd 8%. If I do it twice the text damage will be large, but the watermark will be erased cleanly.

bdbdbd 16% Watermark remains after 1 run. 😵

We need a way to reduce the damage to the character. 🤔

[jankais3r]

Step 1: Prepare a blank page with only the watermark and save it as a temp.png

Step 2: Replace row 22 in process.sh with:
convert $f /Users/xxx/VitalSource/temp.png -compose DivideSrc -composite ../clean/$f

[fofwisdom]

Brilliant!
So many thanks.

[mchangrh]

Unfortunately, this no longer works. Vitalsource has added variable watermarks that flip their gradient (bottom -> top) and also move around the page. If the watermark matches the page, removal is great but if it's offset or inverted, it turns out badly.