Scanning & saving old photos

My bit of advice, vital - in my mind, is to never use Jpeg at this stage in image processing.

Jpeg is fine as a "transfer" format for files to be sent to others, after retouching/resizing.

As long as the recipient will not resize or crop.

Why?

Jpeg is a lossy format and your image is re-compressed every time you resize or crop.

Just use Tif in this case (scan as Tiff) 

Next

Retouch a fell size master Tiff file.

Make a copy, resize it, then sharpen it and ONLY THEN save it as Jpeg -

note that as you do down the Jpeg value scale the compression increases / quality decreases. 

This compression value is something for you to test yourself. But only AT THE END of the process, preserve your master Tiff file for later use / archiving.

I hope this helps
neil barstow, colourmanagement net :: adobe forum volunteer:: co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

The jpg format is designed to produce small files at the cost of reduced image quality, by the use of lossy/destructive compression. The quality loss may not be visible at first, but repeated saving will cause image quality to deteriorate. If you keep saving a jpg again and again, the image will at some point start to disintegrate, and look really bad.

Jpg is a final format to be used for viewing, or possibly printing, but not for editing.

If you are happy with the quality of your edited scans, fine, But if you're going to do more scanning, I strongly recommend setting the scanner to save as Tiff, preferably 16-bit, if that's an option. A 16-bit Tiff can withstand heavy editing without any  quality loss.

As for the files you are going to share on Dropbox, I suggest that you use Export, or Save for Web. The latter lets you include all metadata, which is important if you have added metadata (like the names of people or places) to your files.

Set the quality slider to 85, and make sure that both Convert to sRGB and Embed profile are checked.

I dont't know whta the pixel dimensions are on your scans, but I'd set them somewhere between 1600 and 2500 on the long side.

A common way to do this is to separate how each version is saved. For example:

• For original scans, save at full resolution in a format supporting high quality. 
• For copies intended for distribution, export the copies at a more reasonable file size by maybe lowering the quality level or resolution, but maintaining enough for them to enjoy and maybe print. 

You said the scans at 1200 ppi are typically 1.8–2.5MB each. That number is set by whatever the JPEG compression quality setting was in the software that saved them (the scanning software?); the average size would be higher or lower depending on that compression quality setting.

For the copies you send to family, think about how they might use them.

If you expect them to view the photos on an HD screen, like on a laptop or TV, then you could maybe set them to the size of a 4K display, 2160 pixels on the short side. That would be good enough for viewing on a phone or tablet too.

For printing, suppose you are scanning 4 x 6 inch prints at 1200 ppi. That is 4800 x 7200 pixels, so the math says that’s enough pixels to print at 16 x 24 inches at 300 ppi. Now, if any family members still print, they probably won’t go that big, so you could send them fewer pixels. Let’s assume they might want to include some pictures in a digital book they make, and the biggest book page size they might use is 8 x 10 inches. At 300 ppi, they would need only 2400 x 3000 pixels for an 8 x 10 print.

So then you could set up a workflow in Photoshop (or Bridge or Lightroom) that automates exporting images to 2400 pixels on the short side. That would produce images with fewer pixels than your archived originals, but quite enough for high-quality printing or for viewing on a 4K TV.

The next question is which JPEG compression setting to set up in your workflow. In Save a Copy, the JPEG scale goes from 0–12. The temptation is to set it to 12 because it’s the highest quality…but actually, many recommend that 10 is a much better balance between quality and file size. The reason is that above 10, your eye doesn’t really see the improvement, but file size jumps a lot. Keeping the quality setting between 8 and 10 provides enough quality, while preventing unnecessary file bloat on family devices.

So that would be one suggestion: 2400 pixels on the short side, at JPEG 10 compression. Adjust for your needs and original scan sizes, of course.