GIMP Version: 2.8.14
Operating System: Windows
GIMP Experience: Basic Level

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I am many years rusty with GIMP.

What I am trying do essentially is a color separation task, but my two colors are both shades of gray apparently.

That seems to throw off the tools I tried.

I could not separate the two shades into two layers.

What I have is say a faded and yellowed letter on what used to be white bond paper produced by a laser printer.

What I want to do is to separate the "paper" from the printed text. Then make the paper to be pure white (HEX00000 if I recall correctly). Then do the same to the text but make it the opposite value for black, and then sharpen the edges of characters Then put them the two images back together into one.

The attached image provides an extreme example

I will be very grateful for any direction that you can provide.

Thanks.

Rich2005 has just the method for this! I will look for his explanations for you as I have not done it for awhile.

I found the video, I must have copied it from the net but it is too large to upload, it is 37 megabytes. There is no URL listed so I do not know where it was posted. Rich2005 may still have it. You could PM him as he is a member.

From what I remember, load image, make duplicate to work on. Adjust contrast so that your text differs from the background, select your text (May need to adjust threshold, use color select tool to select text.
Invert your selection so background is now selected, not the text and press delete. You should have only your black text. Now place new layer under it with the color white. You should see your text clearly now.

I really would like for you to see his video as he has some other nice tips.

If you have an email or dropbox, pm me the information and I could email it to you there.

Edit: Nevermind, was tired and didn't realize you want to separate it to pure black & white.
"Faded letter back to like new."
I'd use levels, contrast, OCR and grammar check.
Takes more effort, but can you imagine having to buy pair of glasses just because of messy document?

The Gmic filter suggested below seems good though.

There is a G'MIC filter for this.
G'MIC > Repair > Repair Scanned Document

I used the fiter blighty mentioned then threshold. Keep moving the threshhold only enough so your small writing is still visible

Mike, I found my .pdf of Rich2005 and near the top is the link to his video.

OK; needed a bit of a challenge (since I'm rusty for not playing). Started out using low frequency even script-fu and g'mic (lylejk stencil; thanks again to David for keeping this preset for me; I didn't create the preset by the way; David did) for the result.