BRAW : Aspect Ratio meaning and Anamorphic footages

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antoine

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BRAW : Aspect Ratio meaning and Anamorphic footages

PostTue Aug 27, 2019 10:19 am

Hi,
I don't understand the meaning of the "aspect_ratio" metadata field in the BRAW API. For example with the given SDK Samples A056_08251956_C074.braw we have :
Code: Select all
A056_08251956_C074.braw
Aspect Ratio :  2.35:1
Image Size (Width x Height): 4608 x 2592
==> Width/Height = 16:9
Stretch Factor = Aspect Ratio / ( Width/Height  ) = 1.321875

A056_08251956_C074.braw shown in square pixels looks perfectly fine. So the correct Aspect Ratio should be 16:9. Not sure about the meaning of 2.35, should we stretch horizontally the footage by the computed Stretch Factor ? That wouldn't make sense for this footage because it already looks fine in square pixels.

But then if I have a look at a BMPCC6K sample footage A001_06260425_C006.braw shot in anamorphic :
Code: Select all
A001_06260425_C006.braw
Aspect Ratio : 2.40:1
Image Size (Width x Height): 3728 x 3104
==> Width/Height = 1.201
Stretch Factor = Aspect Ratio / ( Width/Height  ) = 1.998
Corrected Stretch Factor = 2.0

So the Stretch factor would be 2.0 (almost, but let's take into account that the Blackmagic camera had to take a resolution multiple of 8) and it would make sense here (i.e. footage doesn't look fine in square pixels, but does look fine after taking into account the Corrected Stretch factor)

What am I missing ? And how does the camera know that the user is shooting anamorphic ?

Thanks!
Import BRAW into Adobe PPro ! https://Autokroma.com/BRAW_Studio/
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CaptainHook

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Re: BRAW : Aspect Ratio meaning and Anamorphic footages

PostThu Aug 29, 2019 3:17 am

Aspect ratio is actually the ratio for the frame guides, this metadata field is not really in use currently and may change names in the future to more correctly represent the value it stores. There is also a currently known bug that the ratio is stored in the metadata even when the frame guide is not in use.

Anamorphic is/will be indicated by the tag "anamorphic" - currently the P4K and P6K do not write the tags but we hope to in a future update. The UMP G1/G2 already writes the anamorphic tag.
http://www.captainhook.co.nz/blackmagic-cinema-camera-lut/

**Any post by me prior to Aug 2014 was before i started working for Blackmagic**
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antoine

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Re: BRAW : Aspect Ratio meaning and Anamorphic footages

PostFri Aug 30, 2019 6:07 am

Thanks for this info.
Would you have a footage with the "anamorphic" tag so that we can plan ahead this feature ?
Will one be able to know the exact anamorphic horizontal stretch value ? (since we only have it approximately due do the resolution rounding to a multiple of 8)
Or is there a fixed list of all anamorphic values out there ( 1.33 , 1.5 , 2.0 etc.) ?
Import BRAW into Adobe PPro ! https://Autokroma.com/BRAW_Studio/
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antoine

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Re: BRAW : Aspect Ratio meaning and Anamorphic footages

PostSat Aug 31, 2019 12:17 pm

In Resolve 16.1 Beta 2 :

Addressed an issue where the pixel aspect ratio would not be read correctly from Blackmagic RAW files
Import BRAW into Adobe PPro ! https://Autokroma.com/BRAW_Studio/
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antoine

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Re: BRAW : Aspect Ratio meaning and Anamorphic footages

PostFri Oct 25, 2019 12:06 pm

Hello,
Is there any news related to that ? There is a new Camera Update bringing more anamorphic crops so I guess now is the time to have the new metadata ?

Thanks!
Import BRAW into Adobe PPro ! https://Autokroma.com/BRAW_Studio/

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