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How to remove gray garbage background on worksheets?


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My son is doing remote learning and his teacher sends a bunch of png worksheets. She doesn't know how to use a scanner, so the worksheets always have dark gray backgrounds instead of white. When I print them out and my son tries to write on them with a pencil, it's really hard to even see what he's writing. I try to clean them up by playing with the contrast, brightness, and "sharpen". It sort of works, but I'm just hacking. Is there a better way for a noob to do this? 

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I would just resort to tracing with .svg and .pdf to do those. There is also OCR readers to consider.

 

And then there is some other solution like afre text contrast in gmic-qt which was designed for tasks like these.

Edited by Reptillian
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So I tried this, but not sure if it's what you want.

 

1.        Zrq86yG.png Use the color picker to select haflway gray.

                 Click for larger

2.        ACxmN5f.png   Use the Grim Color Reaper to remove the color.

30b8T8B.gif

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I remember using a multistep processing for this:

- convert to grayscale;

- invert image;

- isolate the background levels in a separate layer (remove high-contrast stuff such as text with Median filter);

- substract it from the image;

- invert back;

- clean up remaining noise with Levels filter (histogram there is also helpful to evaluate the quality of cleanup).

 

I later found that there is actually one existing filter that can achieve about the same effect much easier and faster:

Use Effects > Artistic > Pencil Sketch!

Edited by MXI
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My take: https://imgbox.com/zjgE42Y1

 

1. Resize 400% (working in higher resolution might help in multiple ways. The sample was too small);

2. Sharpen max (to make text thicker);

3. Sharpen max (one might be enough, but I found this to be a bit better);

4. Pencil Sketch (tip size max, range min);

5. Resize 50% (still 200% from the source, helps with the next step a bit);

6. Levels (adjust input white to remove as much remaining noise while retaining required details, may also adjust output middle point).

 

 

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While all of these worthy answers/suggestions/ideas are totally with in the spirit of help and cooperation found on Paint.NET, not at all surprising.

 

But I would humbly suggest that instock reach out to the teacher and offer to help her/him with understanding How To Scan a page more successfully. I would venture that help would bring joy to all the students involved today and in future.  

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           Scooter

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4 hours ago, Scooter said:

While all of these worthy answers/suggestions/ideas are totally with in the spirit of help and cooperation found on Paint.NET, not at all surprising.

 

But I would humbly suggest that instock reach out to the teacher and offer to help her/him with understanding How To Scan a page more successfully. I would venture that help would bring joy to all the students involved today and in future.  

I thought about it. I'm not really that smart with that stuff, though. Maybe I could futz with it. But trying to debug it remotely on whatever setup she has? Just a little too far outside my wheelhouse. 

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I think that pencil sketch effect does exactly what I was hoping for. I'm not looking for perfection. It's just a worksheet. Some of you guys have obviously taken it to the next level and then some. I'll play around with it and see how it works going forward. 

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