OK - the results
for anyone interested. I am never going to use my manual photoshop method again!!! Nor will I try the somewhat convoluted internal acrobat method I posted (although it might work - I also found someone post another method https://www.mobileread.com/forums/sho...d.php?t=135660
But that is because I found the PERFECT solutions.
First - ABBY FineReader is far more interesting than I thought - and I am going to likely switch from my Omnipage days to it from now on for OCR and Scanning software (unless I find a way to get a BookDrive scanning system - just discovered that - wish I had seen someone selling their mini unit a few months back - I would have scooped it up ... then I'd try their software. They have a scanning and an editing program - but they also publish Snapter. It looks very promising for cleaning up book scans - particularly those with bent pages (the bend when it is open flat on two pages) - but I don't see how it crops ... at least not quickly and easily. From what I gathered in trying it ... not getting far though ... it does a single page at a time.).
The nice thing about it (ABBY) - is that it will take a double-paged PDF scan and recognize it - and automatically crop/split the pages. I am working on a 600 page book right now - so I haven't seen the final product - but it is taking so long because of the OCR not necessarily the crop.
But for simply cropping - two of the tools that I posted I have tried and they both work like a charm.
I'd give them both two thumbs up. I used both using the graphical interface - although I believe they can both be operated via the command line.
Of the two - one is completely free (Briss), the other is effectively so - but the $35 license is certainly reasonable if you are going to use it often. It works well enough to justify purchasing it.
I'll try and compare these two then: The output of these are identical. The speed of processing is nearly so - but I believe the A-PDF produced the final PDF a bit quicker (but we are talking seconds here - so either way it was quick ... for a 600 page book (300 double sided pages originally).
Both were very easy to use. Briss (which is downloadable through Softforge) is not as pretty or intuitive a user interface. Very basic. But it has an interesting feature. It analyzes the whole document in terms of the two facing pages - and then asks you to set the crop margins - by overlaying multiple pages that are similar on top of each other. You then adjust a grey selection box to set the margins you want to keep in the crop.
That is an amazing feature - not in A-PDF. If you have one of those books that has extreme variations in the original scan (especially if you have large books and old books and you were careful with the spine in scanning them - then in the middle you often have different dimensions ... i.e. the bend in the book causes, for example, the outer margins to be closer to the center) ... this is the perfect tool. Also for when you have scans where there is a good deal and variety of skewing of the page.
So in my 300 converted to 600 page book, as an example, it reduced all 300 double sided images to three categories for setting the crop for the two new pages to be produced. And it tells you exactly what pages (when you mouse over) are included in each set. I set each of the three sets of margins accordingly - and pushed crop - and in less than a minute I had a new, perfect, single paged document.
The controls are limited. Two menu items (File and Action). Pretty much you load the PDF file, it scans it in (it took longer than generating the final PDF to do this - which makes sense given its analysis of each page into the area with text in sets) and gives you an initial crop box, you then adjust those, and push crop and in a few seconds you have a perfect PDF.
It has one other useful feature - you can exclude pages. You just set the numbers or ranges. Here is the link for downloading: https://sourceforge.net/projects/briss/
I give it a 9/10. The one difficulty I had at first was figuring out how to set the crop margins. It puts them there first - and it numbers them - but in my first attempt it had one square across both pages. I couldn't initially figure out how to draw a new crop square - although the instructions say to use left click and scroll. I couldn't get that to work. But I was able to simply select and copy and paste - after reducing the originating square to the first page - and use it for the second. Did the same for the three sets - and it worked perfect. Otherwise it would be closer to a 9.8!! Especially because it is totally free.
Now for A-PDF Page Crop. Again you can operate it via a command line - but I used the graphical interface. It is much more advanced/complicated than Briss. It has a traditional menu bar as well as a viewing area and thumbnail area very similar to Acrobat.
You can also tweak it a bit more in several different ways - that could come in handy for other than a routine cropping.
Again you simply select your PDF and it opens it up. Here you scroll down the pages - just like in Acrobat. Find a good average double page. Then you click a tool to draw a crop square. Do it for both sides of the double page.
Then it has a nice feature. You can tell it to use that crop setting for all pages (or a range). Thus you only have to do it once - and it will uniformly apply to all pages.
Of course - if you have document that varies internally - you can set the pages individually. You get to see the exact image of each page. You can also draw rectangles to divide the page up into quarters for example.
It also has options for automatically drawing a bleed area - and for trimming blank areas. I haven't played with that yet - but a nice feature.
There is also a way to write rules for importing and exporting - but I haven't explored that.
I'd give this a 9.5. If it were entirely free I'd bump it up to 9.9.
Here is the link for it: http://www.a-pdf.com/buy.htm
All in all - these two last options work perfectly - I wish I had known about them all these years I have been doing this manually with photoshop. Would have saved me probably two years on my life!!