Hi,
On some movies, for instance an original 16:9, it will scale just fine if the content is 16:9 and the container is full. The image is scaled so that the left/right edges match the left/right full container edges (with letter boxing top/bottom).
However, some movies that are marked as 16:9, when displayed in a full container, have letter-boxing on all sides. If I match the container to 16:9 the left/right letter-boxing is eliminated. When I watch the source movie in a separate player everything looks fine.
Am I thinking about containers and scaling wrong?
Regards,
Jim
Containers and scaling
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fredjonze
- Posts: 23
- Joined: Thu Mar 02, 2017 6:28 pm
Re: Containers and scaling
More info...
It appears that some of the film makers have taken an aspect ratio different than 16:9 and rendered the film out as 16:9. In DOM if I set the scaling to 16:9 and the container to 16:9 then the left/right borders of the source match the left right borders of the container. However, there is letter-boxing on the top/bottom. That seems to tell me that the source film doesn't have a vertical size of 1080. Since the film was not rendered out with it's real aspect ratio...for instance 1920x800 (as an example), then DOM seems to have problems putting that into a full container. The result is letter boxing on all sides. If I try other scaling (for instance full frame) then the image gets stretched left/right slightly.
Any thoughts on potential solutions?
About half of the films submitted have this problem. The other half were rendered out in true 16:9, so have no problems being put into a full container.
Regards,
Jim
It appears that some of the film makers have taken an aspect ratio different than 16:9 and rendered the film out as 16:9. In DOM if I set the scaling to 16:9 and the container to 16:9 then the left/right borders of the source match the left right borders of the container. However, there is letter-boxing on the top/bottom. That seems to tell me that the source film doesn't have a vertical size of 1080. Since the film was not rendered out with it's real aspect ratio...for instance 1920x800 (as an example), then DOM seems to have problems putting that into a full container. The result is letter boxing on all sides. If I try other scaling (for instance full frame) then the image gets stretched left/right slightly.
Any thoughts on potential solutions?
About half of the films submitted have this problem. The other half were rendered out in true 16:9, so have no problems being put into a full container.
Regards,
Jim
-
Carsten
- Posts: 2804
- Joined: Tue Apr 15, 2014 9:11 pm
- Location: Germany
Re: Containers and scaling
Did you check the 'outline content' option in the preview window? This will show any source related letter- or pillarboxing and is important to use for unknown content such as festival entries.
If source footage contains letter- or pillarboxing, then DOM can not see the internal aspect ratio of the footage. You may need to select 'full container' for DCP container type, and 'no scale' or 'no stretch' for scaling, and, if necessary, manual cropping.
DOM typically tries to fill the chosen container horizontally. This doesnt't work if there is too much black bars above and below in the footage to fit the container aspect ratio. If you want to correct this, you need to crop away the letterboxing, and apply a scaling that fits the internal aspect ratio. The trouble is, you need to find out the actual aspect ratio by calculating/inspecting the active pixel area. Currently, there is no way to automate this. Carl has thought about letterbox/pillarbox detection, but it has not been implemented yet, and there are chances that automatic detection could go wrong.
This happens very often when filmmakers want to create a scope-type image with a cinematic look by applying a scope-type cropping in a 16:9 file (which, technically is masking, not cropping). Very often they do not use standard aspect ratios, thus every file needs to be examined for its active pixel/image aspect ratio to apply proper cropping and scaling without image distortion. I usually create a snapshot in vlc, open up the resulting image in an image editor (or e.g. Preview on my mac), and count active pixels there by e.g. making a selection of the boxes or active image.
Scaling and container choices have changed significantly between latest release (2.10.5) and current test version (2.11.27).
- Carsten
If source footage contains letter- or pillarboxing, then DOM can not see the internal aspect ratio of the footage. You may need to select 'full container' for DCP container type, and 'no scale' or 'no stretch' for scaling, and, if necessary, manual cropping.
DOM typically tries to fill the chosen container horizontally. This doesnt't work if there is too much black bars above and below in the footage to fit the container aspect ratio. If you want to correct this, you need to crop away the letterboxing, and apply a scaling that fits the internal aspect ratio. The trouble is, you need to find out the actual aspect ratio by calculating/inspecting the active pixel area. Currently, there is no way to automate this. Carl has thought about letterbox/pillarbox detection, but it has not been implemented yet, and there are chances that automatic detection could go wrong.
This happens very often when filmmakers want to create a scope-type image with a cinematic look by applying a scope-type cropping in a 16:9 file (which, technically is masking, not cropping). Very often they do not use standard aspect ratios, thus every file needs to be examined for its active pixel/image aspect ratio to apply proper cropping and scaling without image distortion. I usually create a snapshot in vlc, open up the resulting image in an image editor (or e.g. Preview on my mac), and count active pixels there by e.g. making a selection of the boxes or active image.
Scaling and container choices have changed significantly between latest release (2.10.5) and current test version (2.11.27).
- Carsten
-
fredjonze
- Posts: 23
- Joined: Thu Mar 02, 2017 6:28 pm
Re: Containers and scaling
Carsten,
Thanks for the reply. And I've found a fix for now. It appears that the 21:9 aspect ratio is popular with Premiere users. They are rendering to a 16:9 container as projectors can't yet cope with 21:9. If I open the movie in Compressor I can crop the top/bottom by 128 pixels each and then re-render the film to the proper (21:9) aspect ratio. Then, when I add the file to DOM all is well and DOM properly scales the image to the full container.
It won't take long to batch all of the problem films in Compressor.
I'll also review your suggestions.
Regards,
JIm
Thanks for the reply. And I've found a fix for now. It appears that the 21:9 aspect ratio is popular with Premiere users. They are rendering to a 16:9 container as projectors can't yet cope with 21:9. If I open the movie in Compressor I can crop the top/bottom by 128 pixels each and then re-render the film to the proper (21:9) aspect ratio. Then, when I add the file to DOM all is well and DOM properly scales the image to the full container.
It won't take long to batch all of the problem films in Compressor.
I'll also review your suggestions.
Regards,
JIm
-
Carsten
- Posts: 2804
- Joined: Tue Apr 15, 2014 9:11 pm
- Location: Germany
Re: Containers and scaling
If you know the crop factor, you can apply it in DCP-o-matic just as well and avoid another re-encoding.
- Carsten
- Carsten