Easiest way to remove old paper background from graph

[David Cheshire]

This graph was printed in the 1920s on cheap paper that has discoloured badly since. I know I could laboriously scrub out all the old paper but I wondered if there was a quick and easy way to remove the old paper background leaving all the lines and data points intact?

Thanks.

[Wosven]

There are certainly different ways to do it, 2 to came to my mind...

It's only getting rid of the background, other layers to get a better graph can be added.

scan0001a.afphoto

[firstdefence]

You can pretty much nail that image with a single filter such as Black and White filter with the yellow slider set to 300% basically far right.

[David Cheshire]

14 hours ago, Wosven said:

There are certainly different ways to do it, 2 to came to my mind...

It's only getting rid of the background, other layers to get a better graph can be added.

scan0001a.afphoto

Thanks, that looks very good. For a complete newbie to Affinity would you explain how you did it please? 

Kind regards, David

[David Cheshire]

13 hours ago, firstdefence said:

You can pretty much nail that image with a single filter such as Black and White filter with the yellow slider set to 300% basically far right.

That's certainly very quick and easy, thanks!

[Wosven]

Hi @David Cheshire

I spend years working on CMYK image. So, what I did first is what I would have done on a CMYK image, using Level ajustements. I did it directly on the RGB channels, but it's easier on the CMYK ones. And you can do it easily in AP.

 

You add a Levels adjustement layer, and it'll show you the color density for all channels, or for each channels. In CMYK, it's easier to understand: we want less Magenta and less Yellow in the white parts of the image.
Once the CMYK mode selected, it's displaying mainly peaks for black, magenta and yellow.

 

We can select the Magenta channel:

 

To get rid of the Magenta peak, we move the Black cursor "before" the peak.

 

We can do the same on the Yellow channel:

 

Nothing to modify on the Cyan channel:

 

On the Black channel, we can lighten the background, and modifying the other slider, we can darken the lines:

 

An old trick is to dupplicate the layer, to check if it improve the result. In this case, I did it and just modified a little bit the Black channel:

===========

Doing this in the RGB channels can add colors on the lines:

For corrections, I would use a Black and White adjustement to get rid of the colors, and another Levels (but it could have been a Curves or a Brightness and contrast layer):

[Wosven]

With the TSL layer, it's sort of the same idea:

Instead of channels, you've got preselected colors. We want to desaturate (second sliders) the red and the yellow, and also lighten them (third sliders).

 

We can also use a color picker to select the background and do the same:

 

Everything is grey, but the background isn't white, So I add a Curves adjustement, to lighten the background and darken the lines (it could have been a Levels adjustement).

 

=======================

The resulting file:

scan0001a.afphoto

 

[firstdefence]

I quite like the more sympathetic removal of colour using the HSL filters picker tool to select the background colour and using the luminosity slider to lighten the now grey background but leaving some of the paper texture, and again it's a single filter shot...

The integrity of the graph, lines and numbers is also maintained to a cleaner result and it looks "authentic"

[David Cheshire]

Thank you both for your replies, they are just what I needed to know and I have learnt a lot about AP in the process. Thanks especially to Wosven for the very detailed step by step explanations which are very useful to a newbie.

Kind regards, David