Need help for restoring old BW pictures

[ALAR]

Hello everyone, I'm new to the forum. I hope I can find (and even offer) advice and help.
I personally need to use GIMP because I want to publish a photography book (ebook and paperback) of about 40 historical black-and-white photographs of monuments and landscapes dating back to the 1950s, all taken with the same camera at the same time on the same day.
The photographs, measuring approximately 10" x 6" (20cm x 15cm), have already been physically "cleaned" and scanned into high-quality lossless TIFF LZW files at 600dpi, approximately 6000x4500 pixels each, about 40MB each.
I'm very familiar with audio-video editing programs, but I'm having some difficulty with photo editing, which is a whole other ballgame! :-)

I'm asking for your help in defining a workflow to apply to all the photographs. I'm personally capable of rotating, cropping, and using the Heal (H) command to remove scratches from photographs with satisfactory results, but I need your help figuring out how to correct contrast and brightness and improve the final quality of the photo.

Thank you, I hope someone can help me!

P.S. I'm attaching an example (JPG format, so really downscaled compared to the TIFF files). All the other photographs share the same attributes.

[denzjos]

Try something that isn't complicated : Colours / Levels / Auto Input Levels

[rich2005]

I might try a little sharpen. Try the Wavlet Decompose filter: see: https://docs.gimp.org/3.0/en/plug-in-wav...mpose.html

This a 40 second example: I would avoid using the layer group option until you know how it works. I put a original copy on top just to show before / after.

https://i.imgur.com/PsAxPcn.mp4

There is also the gimp_gmic_qt plugin http://www.gmic.eu which has several sharpen filters + others

[sallyanne]

I have a little blog that shows my workflow - with gimp to restore photos
https://howtrp.blogspot.com/search/label/02.%20First
Follow the numbers on the right side

[ALAR]

Hello everyone and thanks again for your precious replies. I'm sorry for the delay in the answer, but this is a very busy period of time for me. However, I think I managed to achieve some good results that I'm sharing with you all. I would love to receive some honest feedback and criticism to enhance even more what I have done.
Based on the great ideas you have given me, first of all I rotated correctly and cropped the scanned potographs for a neat composition effect. This was difficult sometimes, as some of the edges became badly trimmed, so, with a lot of patience and trial and error, I used the CLONE tool and the HEAL tool to "rebuild", little by little, the void edges of the pictures. Yes, if you zoom in 800% you can definitely notice some strange things happening here and there, but that's not the case for a 100% or even 200% zoom.
Then, I applied Colors -> Levels: the only adjustments I made is that I set the black and white INPUT levels based on what I could see on the Histogram (always around 30 - 240 and, depending on the type of picture, I set the greys (mid points) around 1,20 - 0,90. I left the output levels to standard 0 - 255.
Then I applied Filters -> Enhance -> Noise Reduction, noticing good results with Force around 6-8.
Then Filters -> Enhance -> Unsharp Mask, Radius 3,4, Amount 0,5, Threshold 0,0.
Is there anything you would suggest me to add, more? Is there a "safe setting" regarding black and white input/output levels, considering these edited pictures are going to be printed ona photographic book? Thank you very much.
Please note that these are 500% closeups crops from the original big images.