I have a particularly nasty "original" of a very old blueprint. There is a fair amount of chance that the original is actually a color copy of the "lost real original", but nevertheless, this is the best we have and we need to dig out a readable image out of it.

I am looking for advice/guidance how to make the most out of this scan.
Seems like any of the 'stand-alone' approaches (levels, treshold, multiple layers of hard-light) is sub-optimal. So far the wavelet sharpen gives me the most detail, but I can't get rid of the background. Any, even the smallest help is appreciated.Please see the attached file and post your results.

I've done 2 tries but it's too difficult me to improve the sheet. I hope someone to be able to do it notabenem.

I tried it with several filters and just couldn't get rid of all that noise, desaturate did make it a little more clear, but not much. I think this one is going to take a magician.

Do you have the original blueprint? If so, can you rescan at a higher resolution and a better format (TIF, PNG)? With an image like this how you scan is very important, have a look at A few scanning tips.

As that is just a segment, cleaning it up won't help.

I'd suggest redrawing it by hand based on why the eye can perceive and then ring out the wires of the actual cct to confirm the correct relay/contact and switch connections.

-Rob A>

Here's the best I could do with this scanned blueprint...

Looks better Wallace, it is almost tempting to use that for a guide and redraw the whole thing. At least now you can see the lines.

I do have the 'original' as well as the raw scanned TIFF (200dpi, 24bit). The reason I gave you the JPG because the png (8MB) did not fit the size restrictions of this board. Nevertheless I do not think the lossyness of JPG makes a difference in this case. Higher DPI won't help either, just the spots will be bigger in terms of pixel size.

What did you do Wallace, to achieve your result?

I desaturated the image, applied curves to make it as white as I could without losing the lines. Duplicated the image and did a color to alpha with white. duplicated that and set the layer mode to multiply. Duplicated that a few times and merged everything.

Archive (zip) the PNG with the highest compression ratio and attach it here.

PNG already employs the LZW compression algorithm - the same as used in ZIP.
Anyway, did as told. The final file size was actually 2kb bigger than without compression.

I think Roba's idea would be the best, redraw then put the numbers back in.

While redrawing would be an option for this specific sample, we have thousands of such drawings.