[ imagination-Bugs-3196281 ] Anamorphic pixel aspect ratio correction
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Category: Backend
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: lxp (lxp13)
Assigned to: Robert Chéramy (tibob42)
Summary: Anamorphic pixel aspect ratio correction
Initial Comment:
If you select an anamorphic output format like VOB DVD PAL 720x576, Imagination doesn't resize the images according to the anamorphic pixel aspect ratio. This results in vertically or horizontally stretched images for 4:3 PAL (720x576) or 4:3 NTSC (720x480). For 16:9 PAL (720x576) the problem is even more visible.
I tested this with SVN revision 591 and did a quick hack to allow producing slideshows with correct aspect ratio. I have attached the patch, but it is not directly ready for inclusion because it forces 4:3 aspect ratio. Nevertheless it should work fine when the video_ratio variable is initialized with the correct aspect ratio.
I think there is a main issue in the aspect ratio/resolution handling of Imagination and I am not completely sure how you would like to fix or not fix it.
My opinion is that you should be able to produce a slideshow in a 4:3 or 16:9 aspect ratio (so you have to select 4:3 or 16:9 when creating a new project), whereas Imagination currently only allows to set the resolution for the project.
The reason for this is that the aspect ratio itself changes the appearance of the slideshow, while the resolution itself can scale up/down with no impact on the appearance.
Moreover I think that setting the resolution in the project settings is more or less useless (don't know if it is eventually necessary for animations or so), so the resolution setting could be moved to the export dialog, where you should only be able to select the resolutions appropriate for the aspect ratio.
I would like to further discuss this issue with you. You can also contact me on IRC (Freenode; Nick: lxp).
PS: For testing I used these two aspect ratio test images:
http://www.mediacollege.com/video/test-patterns/aspect-ratio-circles.html
http://hometheater.about.com/od/hometheatervideobasics/ig/Spears-and-Munsil-Test-Disc/Spears-Munsil---Geometry.htm
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Comment By: Nobody/Anonymous (nobody)
Date: 2011-11-12 23:34
Message:
I'm surprised noone else has complained about this... i noticed it very
quickly (also that part of my 4:3 images are being chopped off even though
my vob output is 4:3 !) but since it is open source i figured i could fix
it... i used this patch and it worked for my purposes. As noted, this
hack won't work if i wanted 16:9 output aspect ratio... a real fix is
needed.
The basic problem is that VOB files don't have square pixels...
The desired output aspect ratio needs to be moved into the project file
since it deeply effects the visual effect.
The output resolution could be moved into the export dialog (although i'm
ok with having it in the project file) because it is only at export that we
need to deal with the fact that VOB files don't have square pixels (a
resampling is required at that point).
Thanks for the otherwise excellent software,
-Ted Merrill
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Comment By: Giuseppe Torelli (gt67)
Date: 2011-03-02 08:31
Message:
Hi,
I appreciate your kind work. Unfortunately the code is frozen since we are
waiting for the translators to complete the translations of the new strings
introduced in the 3.0. Do you have a gmail account? We can chat there.
Thanks
Giuseppe
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Comment By: lxp (lxp13)
Date: 2011-03-01 09:04
Message:
By the way, I should note that I always disabled "Rescale images to fit
desired aspect ratio" because that option caused even more confusion. It
resulted in inconsistent aspect ratio between cropped images and images
with border.
I haven't looked into that issue after doing the anamorphic pixel aspect
ratio hack because I don't really need this option for my current project.
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