PowerShell epub EBook optimizer
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Utility script that can read a ebook epub file and try to compress the images a bit more, so the total epub file gets smaller.

! Does not work on epub files containing .gif and .svg files.   !
! Only epub files containing .jp(e)g images are supported.      !
! Png file optimizations are experimental                       !


Usage:
.\epub_ebook_optimizer.ps1 <path\myebookfile.epub>  # single argument is the same as providing arg -epub <path\myebookfile.epub>
.\epub_ebook_optimizer.ps1 -epub <path\myebookfile.epub> [-limit <size as bytes>] [-compression <0..100 as procent>]


Version History:
14/11/2021 : First versions.
             Made a few tweaks to it in the same day.
             Last version was in fact non-working, because i commented out the Optimization method for debugging reasons, and forgot te re-enable the method when pushed to repo.
15/11/2021 : Created a more optimized and efficiënt version (not in terms of speed, but in optimizing the end result epub file).
16/11/2021 : Preperations for converting .png files to .jpg.
             Lowered the default size for epub archive files from 100Mb to 98Mb.
17/11/2021 : Created version that can handle .png files (converts files to .jpg format).
20/11/2021 : Small improvements
             Cleanup temporary leftover files at startup, if script would be early aborted by the user.
21/11/2021 : Discovered a bug in the xhtml that is not replaced in the optimized .epub archive.
17/05/2024 : Found that some epub files OPF XML data, contained a corrupted or incorrect DTD.


Tips & tricks:
- Loop trough a folder and optimize epub files in bulk
PS C:\epub_tool> $files = @(Get-ChildItem -Path C:\SomePathWithFiles -Filter *.epub)
PS C:\epub_tool> $files | % { .\epub_ebook_optimizer.ps1 $_.FullName }

- The script shows "WARNING: [!] No epub action needed! Size is okay."
Always check you use absolute paths instead of relative paths.
For example, dot sourced paths in Powershell will not work.
PS C:\epub_tool> .\epub_ebook_optimizer.ps1 .\MyEBookFile.epub                # will not work
PS C:\epub_tool> .\epub_ebook_optimizer.ps1 "C:\epub_tool\MyEBookFile.epub"   # does work