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How to undo/straighten/flaten a perspective view

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tim
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How to undo/straighten/flaten a perspective view

Post#1 by tim » 19 May 2018, 06:07


There was a question on gimpchat. That got me experimenting with perspective tool.
Applying a perspective on a perfect rectangle is easy. But how to do the reverse when you have an image that has perspective applied and you want to straighten/flatten it out into a rectangle again?
In GIMP 2.10 there's a transform with handles tool so that's easy to work with but how to do it in GIMP 2.8 with existing perspective tool.
The answer is by doing multiple perspectives, 2 of them at least if you match align/match 2 corners.


1. Create guides of rectangle you want to match making 2 corners match intersection of guides (bottom 2 corners for example).
Screenshot from 2018-05-18 22-30-14.png
Screenshot from 2018-05-18 22-30-14.png # (140.01 KiB) Viewed 3936 times (Thumbnail | Recognize | Sq Tile | LNFI)
2. Use the free select tool to select your not yet rectangle shape (intersections of longitude and latitude)
3. Use the perspective tool to drag an unmatched corner to match the guides (top left corner for example).
Screenshot from 2018-05-18 22-31-49.png
Screenshot from 2018-05-18 22-31-49.png # (220.38 KiB) Viewed 3936 times (Thumbnail | Recognize | Sq Tile | LNFI)
4. Apply the transform/perspective. Anchor layer.
Screenshot from 2018-05-18 22-33-20.png
Screenshot from 2018-05-18 22-33-20.png # (187.73 KiB) Viewed 3936 times (Thumbnail | Recognize | Sq Tile | LNFI)
5. Free select to select your not yet rectangle shape again (now having 3 corners matching guide).
6. Use the perspective tool to drag the remaining unmatched corner to match the guides (top right corner for example)
Screenshot from 2018-05-18 22-34-32.png
Screenshot from 2018-05-18 22-34-32.png # (188.98 KiB) Viewed 3936 times (Thumbnail | Recognize | Sq Tile | LNFI)
7. Apply the transform/perspective. Anchor layer.
8. Now you have a close to perfect rectangle that you can scale to whatever dimension you want.
Screenshot from 2018-05-18 22-35-21.png
Screenshot from 2018-05-18 22-35-21.png # (197.72 KiB) Viewed 3936 times (Thumbnail | Recognize | Sq Tile | LNFI)
aka Tin
World Food Program | Good Deeds Forum

         

Issabella
Script Tester
3rd Place
3595 Post(s)

Post#2 by Issabella » 19 May 2018, 06:24


Thank you so much Tin, nice explanation about perspective tool.
Issabella

Don’t be afraid to start over. It’s a new chance to rebuild what you want.

Pat625
Tutorial Creator
2nd Place
4512 Post(s)

Post#3 by Pat625 » 19 May 2018, 07:27


Thank you, Tin. I have had problems trying to straighten a perspective and now I have a method to try instead of just fussing with it! Your explanations and screenshots were precise which made it easy to understand.

tim
GL Blogger
1st Place
5635 Post(s)

Post#4 by tim » 19 May 2018, 18:52


Some graffity can only be seen from a certain angle.
I thought I would have some fun with this method and see what some of the art would look like if it was possible to view straight on.
Found a good example here: http://www.dailymail.co.uk/news/article ... ngles.html
What it looks like when straightened (I used a black background so that i could easily tell when my corners are generally lined up while perspective tooling.
german_railing_graffity_edited.jpg
german_railing_graffity_edited.jpg # (217.04 KiB) Viewed 3903 times (Thumbnail | Recognize | Sq Tile | LNFI)
aka Tin
World Food Program | Good Deeds Forum

         

Pat625
Tutorial Creator
2nd Place
4512 Post(s)

Post#5 by Pat625 » 20 May 2018, 07:03


I would think that it took a lot of time and calculation to paint on railings and things so that you could only see the painting at a specific angle. I don't like math that well!!

tim
GL Blogger
1st Place
5635 Post(s)

Post#6 by tim » 20 May 2018, 14:43


Pat, I think you just gave me an idea for a script .
Hang in there, I'll share it when I am done writing it and testing it.
aka Tin
World Food Program | Good Deeds Forum

         

rich2005
GIMP Guru
22nd Place
178 Post(s)

Post#7 by rich2005 » 20 May 2018, 15:01


I wonder if the wheel is being reinvented again ;)

Image

tim
GL Blogger
1st Place
5635 Post(s)

Post#8 by tim » 20 May 2018, 15:35


Oh so close.... Rich. I haven't written script yet but I will soon.
I thought like custom font instead of file font definition, you give a file with image of railing and paths defining each railing then you can choose image of your choice and it then uses perspective to chop up the image and paste them on the railing.
So users can create railing image and path definitions for those railings which can then be reused by other users.
That hasn't been done yet has it?
aka Tin
World Food Program | Good Deeds Forum

         

rich2005
GIMP Guru
22nd Place
178 Post(s)

Post#9 by rich2005 » 20 May 2018, 15:40


..That hasn't been done yet has it?..
No..keep on going..

tim
GL Blogger
1st Place
5635 Post(s)

Post#10 by tim » 20 May 2018, 15:44


Sweet, this should be fun.
aka Tin
World Food Program | Good Deeds Forum

         


GIMP/GL:  🡆 Tutorials | Tips | Questions | Interests | Script Requests
Recommendations:  Index | Top 10
Resources:  Python-Fu Plug-ins | Scheme-Fu Scripts | GIMP
Python:  Lessons | Questions | Exercises
The Arts:  GIMPed | GIMPed Photos | Other | Contests | Public Domain Images | Isolated Images | Blender
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