9 Mar
2016
9 Mar
'16
2:53 p.m.
Hi,
A problem that I have run into a few times:
I can't find a convenient way to remove the black bars from letterboxed
content with non-square pixels and non standard aspect ratio.
An example:
Content with letterbox (62 pixels top and bottom) is 720x576 and has a
pixel aspect ratio of 1.42:1
Display aspect ratio is 1.78:1 (16:9), so the displayed image is
1024*576 including the letterbox and 1024*452 with the letterbox
removed. This gives a aspect ratio of 2.27:1 which to my knowledge does
not fit any of the predefined containers.
- With "Scale to" set to 16:9 the picture is not distorted but shown
with letterbox and not filling the container.
- Cropping top and bottom bar distorts the image because the display
aspect ratio is fixed and not the pixel aspect ratio.
- Changing "Scale to" to "no stretch" distorts the image because the
pixels are displayed square (which they really are not).
So what I need is a "Scale to" option that keep the pixel aspect ratio
fixed to whatever is reported with ffprobe (specified in the video
header?) - That way I can crop the image without distorting it.
Have I overlooked an obvious way to make the useful part of the image
fit the height of the container without distortion?
The example content is available here:
https://www.dropbox.com/s/2qeex6oautq8vlj/06_Oscar_1.mpg?dl=0
Cheers,
Christian
9 Mar
9 Mar
3:40 p.m.
New subject: [DCP-o-matic] How to un-letterbox content with non-square pixels without distortion?
Hmm, I just tried it and at first sight, it looks as if DCP-o-matic is doing everything
right.
You are right in that there is no dedicated container format for this type of source
footage, but that is how DCI meant this to be.
DCP-o-matic applies the right scaling to 16:9, and tries to fill the chosen flat container
as much as possible. The best container for this type of footage is flat/1.85.
That leaves black bars on the sides (1920->1998) and of course the letter boxing in
place. To get rid of the side bars, you choose 'Scale to Flat/1.85', then crop
top/bottom to adjust for the slight stretch from 1920 to 1998.
It's impossible to have dedicated preset for every imaginable aspect ratio and target
size. I have opted for a universal x/y crop/scale GUI option before, but I know what
inexperienced users would make of it, so, I would rather avoid it.
It's not a bad thing to have letterboxing in your DCP - The Hateful Eight was
delivered in a 2.76 AR (4096*1484), letterboxed in a scope container (4096*1716).
- Carsten
Am 09.03.2016 um 15:53 schrieb Christian Hove via DCPomatic:
Hi,
A problem that I have run into a few times:
I can't find a convenient way to remove the black bars from letterboxed content with
non-square pixels and non standard aspect ratio.
An example:
Content with letterbox (62 pixels top and bottom) is 720x576 and has a pixel aspect ratio
of 1.42:1
Display aspect ratio is 1.78:1 (16:9), so the displayed image is 1024*576 including the
letterbox and 1024*452 with the letterbox removed. This gives a aspect ratio of 2.27:1
which to my knowledge does not fit any of the predefined containers.
- With "Scale to" set to 16:9 the picture is not distorted but shown with
letterbox and not filling the container.
- Cropping top and bottom bar distorts the image because the display aspect ratio is
fixed and not the pixel aspect ratio.
- Changing "Scale to" to "no stretch" distorts the image because the
pixels are displayed square (which they really are not).
So what I need is a "Scale to" option that keep the pixel aspect ratio fixed to
whatever is reported with ffprobe (specified in the video header?) - That way I can crop
the image without distorting it.
Have I overlooked an obvious way to make the useful part of the image fit the height of
the container without distortion?
The example content is available here:
https://www.dropbox.com/s/2qeex6oautq8vlj/06_Oscar_1.mpg?dl=0
Cheers,
Christian
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11:19 p.m.
New subject: [DCP-o-matic] How to un-letterbox content with non-square pixels without distortion?
Hmm, I just grabbed some images and checked the pixel dimensions - one thing is a bit
weird, QT Player and an exported single image tell me the source pixel dimension is
720*404 (including letterboxing) - yet DCP-o-matic says it's 720*576?
If I strip the letterboxing in Photoshop, the content is 720*319. That's a 1:2.25 AR.
Quite common to put side cropped CS images on DVD like this in order to reduce the
letter-boxing somewhat.
A bit weird, also that DOM is giving the vertical dimension as 576 when it seems to be
only 404, but it is still possible to create a proper DCP from it. You just need to
acknowledge the necessary letter-boxing.
VLC gives dimensions in statistics as 720/576, and extracts/snapshots a 1024/576 still
(incl. letterboxing), content stripped from letterboxing is 1024/454. But that is just a
different way to apply the anamorphic stretch (horizontal stretch vs. vertical
compression). It's both 1:2.25.
- Carsten
14 Mar
14 Mar
4:50 p.m.
On Thu, 10 Mar 2016 00:19:45 +0100
Carsten Kurz via DCPomatic <dcpomatic(a)carlh.net> wrote:
Hmm, I just grabbed some images and checked the pixel
dimensions - one thing is a bit weird, QT Player and an exported single image tell me the
source pixel dimension is 720*404 (including letterboxing) - yet DCP-o-matic says it's
720*576?
The pixel aspect ratio is marked in the header as 1.42:1 so maybe that
has something to do with it...? VLC and ffmpeg pick it up as 720x576.
If I strip the letterboxing in Photoshop, the content
is 720*319. That's a 1:2.25 AR. Quite common to put side cropped CS images on DVD like
this in order to reduce the letter-boxing somewhat.
A bit weird, also that DOM is giving the vertical dimension as 576 when it seems to be
only 404, but it is still possible to create a proper DCP from it. You just need to
acknowledge the necessary letter-boxing.
VLC gives dimensions in statistics as 720/576, and extracts/snapshots a 1024/576 still
(incl. letterboxing), content stripped from letterboxing is 1024/454. But that is just a
different way to apply the anamorphic stretch (horizontal stretch vs. vertical
compression). It's both 1:2.25.
Do you think DoM is getting something wrong here?
Cheers,
Carl
15 Mar
15 Mar
12:12 p.m.
New subject: [DCP-o-matic] How to un-letterbox content with non-square pixels without distortion?
Am 14.03.2016 um 17:50 schrieb Carl Hetherington via DCPomatic:
Do you think DoM is getting something wrong here?
I am not sure, I have to think over it again. At least it IS possible to scale the content
properly with DCP-o-matic, although not in a click'n-go fashion, but that is normal
with arbitrary aspect ratio content.
- Carsten
3331
days inactive
3337
days old
4 comments
3 participants
participants (3)
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Carl Hetherington -
Carsten Kurz -
Christian Hove