Removing paper staining

[Rich42]

Hi there, I wonder if anyone can give me some advice or help. I have a scan of a drawing, the paper has become very stained and I want to remove this and leave just the pencil drawing. I have tried a few tools on Photo 2 but I'm not particularly getting anywhere. Can somebody suggest how I could go about this please. I've attached screen shot of what I'm trying to work with. Thanks

[Ldina]

@Rich42 I played around with this and found it to be quite a challenge. You have at least two impediments....color and contrast. Some of the thin pencil lines are lighter than the reddish blotches, which makes it tough to isolate and retain them based on luminosity. Zooming in, I saw that the color also permeates the gray pencil lines, which makes it hard to isolate by color. Without a lot of manual cleanup, I suspect you will have to settle for 'improvement'. Someone may have some far better solutions.

I tried a few things. Frequency Separation (Median Blur method seemed to work best). Keep the high frequency layer and turn the low frequency layer white. Then try things like noise reduction, desaturating, etc..

I also tried Detect Edges, then inverted it, applied some noise reduction, Levels, etc. 

My third attempt used a very steep Curves Adjustment to darken the pencil lines. I followed this with an HSL adjustment, targeting the reddish color and desaturating it (-100%) and increasing the luminosity (+100%). Unfortunately, it's still pretty blotchy due to the fact that many of the blotches are darker than your thin pencil lines. 

One additional approach is to look at the individual red, green and blue channels. Not surprisingly, the Red channel seems to be the cleanest of the bunch (since the color cast is primarily red) and provides the best separation between pencil lines and the reddish coloration. Create a Grayscale Layer based on the Red channel as a starting point. You still have the problem that blotches are darker than many of your thin pencil lines. 

Perhaps employing an AI alternative will do a much better job, but I have almost no experience with artificial intelligence. Hopefully, someone here can provide a better solution. 

[carl123]

1. Add a Black & White adjustment Layer (make sure the adjustment layer is a child layer of the Image, not above it)
2. Max out the yellow slider in the Black & White adjustment Layer 
3. Duplicate the Image Layer (including the adjustment layer)
4. Set Blend Mode on the duplicated layer to Linear Burn for a bit more of a contrast

Can't tell if that works for the rest of the document, due to only having a small sample to look at

Note: You may be able to increase some more of the details but no time to play with that today

[NotMyFault]

I would utilize the colors of the scan. The red channel looks much cleaner than green and blue. The mold has actually green/blue color, so we can use this to selectively suppress the mold and keep the contrast between paper and lines drawing high

1. add channel mixer
2. Red channel
   1. increase red to about 160
   2. subtract green -35
   3. subtract blue -35
3. green and blue: set to zero
4. add another channel mixer to use red channel for all RGB channels
5. add curves adjustment to boost contrast
6.  maybe sharpen a bit

 

 

scan clean.afphoto

[Ldina]

@carl123, @NotMyFault Both superior methods!! Thanks.

[thomaso]

1 hour ago, carl123 said:

1. Add a Black & White adjustment Layer (make sure the adjustment layer is a child layer of the Image, not above it)
2. Max out the yellow red slider in the Black & White adjustment Layer 

2a. red max. / yellow as you like.
3.  Add a Levels Adjustment -> move the Black slider to increase contrast as you like.
4.  Thanks to @carl123

[Rich42]

This is brilliant, thank you all for your help. I shall give this a go.