True Pseudogrey in GIMP

Pseudogrey target ref:  http://justpaste.it/files/justpaste/pgrey1.png (this target has precisely 1786 tones)
Main motivation came many years ago.   Here's a cool experiment and you will see why.   Create a new image 512 by 512 and run grandient tool (foreground/background colors black and white) across a horizontal (end to end) and if you do it right, count how many colors you have and you will have 1786 colors tones.   Pretty cool since a regular desaturation only gives you 256 colors tones.   Anyway, I only managed to get 1786 colors once (usualy get less) but I didn't save that gradient as I should have.   lol
Below's the tutorial.   Note the settings for the Sample Colorize plugin (Hold Intensity and Original Intensity unchecked; very important).  Also note Subcolor box is checked:
1.  Open both Pseudogrey reference image and your target image.
2.  Do whatever necessary edits that you want on your Image Target (in this case, I just did an autolevel).
3.   Run Sample Colorize Plugin (built in GIMP plugin) with the following settings and the Pseudogrey Target as the Sample:
4.   Click Get Sample Colors Box then click Apply and Close.   You are done.   Example below ( (click image to see big result;  saved as PNG {lossless} format since saving as jpeg will loose tones).
Note the Colorcube analysis below; 1786 tones:
I started a parallel thread at GIMPChat and there is some very cool additional info that might benifit some.
patdavid converted this flow into an automated script-fu which he shared here and it works great; happy I am.  Below's the official host site for the Script-fu.
David first announced that he will implement Pseudogrey with G'MIC at this thread.   Very cool news indeed.  
patdavid decided to create Pseudogrey output using javascript w/ HTML 5 elements (requires a modern browser) too.   Cool stuff.   Details:  http://gimpchat.com/viewtopic.php?f=10&t=4245&p=57407#p57406
Smarter guys then I ever will be has had some extensive discussions and those comments are worth sharing this link:  http://www.flickr.com/groups/gimpusers/discuss/72157630198258246/
Delaboratory (version now supports Pseudogray; pretty cool indeed.  http://code.google.com/p/delaboratory/