Step 1: How to scan larger-than-letter/A4 sized pages from a book?

For scanning, don't need to perfectly align to a page size using the scanner. Use the scanbed, put the page in the middle - we'll crop later. Scan all the pages using this method. Scan to JPG files.

Step 2: How to crop them efficiently?

NOTE:

  • if you need to rotate each page, I found it easier to rotate each page first before cropping all at once. See "How to rotate"
  • before doing any transformation, scale the image if they're too big in pixels (e.g., from 7000 -> 3000). And adjust the ppi to 72 ~ 200. This will bring down the exported PDF file size, and make later rotation faster.

In GIMP, drag the first page in, manually select the desired page region, then right click -> image -> crop to selection. This will crop the canvas to the desired page size.

Drap the 2nd page in. Note that it's on the 2nd layer. Notice that only a "window" (of selection size) of the 2nd image is shown. Use the drag tool to move the desired portion of this image into the "window".

Repeat the above process for the rest of the pages. Now you should have each page in their own layers.

>>> NEW WORKFLOW: Rotate and Crop Layers Using Guidelines <<<

Creating guide lines helps rotation:

  1. use select tool, from top-left to bottom-right corners.
  2. Image -> New Guidelines from selection. NOTE - cancel selection now by clicking anywhere on the canvas (1). Otherwise later rotation only applies to the selection region.
  3. Now use the guidelines to
  4. rotate each page: Shift-R (or "Tools -> Rotate") for layer rotation (not whole image). Drag to rotate. Shift-Drag to rotate at certain degrees.
  5. move each page to the guideline
  6. Finally, selection on the guide line region, then image -> crop to selection. This will crop all layers all at once.

Step 3: How to compile them into PDF?

GIMP 2.10 supports exporting layers as pages to a single PDF file. Export -> set file name to some_thing.pdf -> press export. A dialog pops up about PDF exporting, choose "layers as pages" (it lets you specify the order).