Blackmagic Forum

Hello!

-iPhone footage captured in Apple Log, 4K ProRes 422 HQ using Blackmagic Camera App on iOS.
-1.55x Anamorphic mobile lens was used in front of the camera.

So, native clips are 3840x2160 (16:9). As a test, I shot 2 clips. The first clip uses BMC App's 1.55x desqueeze option which gets buried in the clip's metadata. The second clip was also shot with the Anamorphic lens but not using the desqueeze in-app, to see if manually setting the pixel aspect ratio in Resolve would help with the problem.

I want to finish in Academy Scope, so the Resolve project is set to 4096x1716 (2.39:1). Image sizing input and output are set to "Centre crop with no resizing". Resolve detects the clip shot with a 1.55x pixel aspect ratio and appropriately applies the pixel aspect ratio. Great. The manual clip I adjusted to match under clip attributes. Both clips now match, now I do my scaling calculations.

Native clip size: 3840x2160 (1.78:1)
Finishing resolution: 4096x1716 (2.39:1)

3840 * 1.55 = 5,952 (of note, the clip shot with 1.55x in-app shows up in the operating system as 5952x2160, but in Resolve as 3840x2160) this aspect ratio is 2.76, and so now I should crop to 2.39 and then scale to 4K UHD Scope.

2160 * 2.386946 = 5155.80336
So I expect the 2.39 extraction to be 5156x2160

Now to check the numbers to scale from the extraction to the final output:
4096 / 5156 = 0.794444
1716 / 2160 = 0.794444

I check using both width and height and the numbers match, so I know my extraction calculation is correctly 2.39. If I take 0.794444 and input it into Zoom in the resizing module, and save this as a preset, I should expect to be able to modify the "Input Presizing" under clip attributes of any clip and it should scale the 5156x2160 extraction down to 4096x1716. However, this is not what the footage does. The footage is scaled down as seen in the attachment. The first image is with the Input Presizing of 0.794444 applied. The image is smaller than the final output, yet the extraction should be larger than the final output and scaled down, not up. The second image is how the footage is displayed "Centre crop with no resizing" and no other modifications. The third pic is of the expected result (I cheated by up-scaling manually to mimic what the input presizing should be doing). If I were to speculate, it looks like when going from a 1.0 to 1.55 pixel aspect ratio, Resolve is transforming the image while maintaining the 3840 width in pixels. So, its compressing vertically and ending up with something like 3840x1390. This is not what happens when using this form of scaling with a 'real' cinema camera system.

Please keep in mind that I have used this scaling workflow for 15 years on set with all flavours of Anamorphic lenses, on all cinema camera systems from Alexa 65, 35 etc, Sony Venice 1+2, Red etc etc. This approach is vetted through Deluxe/Technicolor (Co3/Picture Shop). Meaning I know the math is sound and the method should achieve the results I expect. So, what I'm wondering is if there is some way Apple is automatically modifying their clips before they are transformed in Resolve? Has the BM Camera App embedded anything in the metadata that is making Resolve transform the image? Is it perhaps just a bug with this media? Has anyone else experienced this (not many people shoot Anamorphic on mobile so I know its a long shot)? Maybe there is something I am overlooking?

Any insights would be grateful!

How do you know the lens isn't distorting the image on the edges and adding the vignette?

BTW, as I always tell anybody who's shooting anamorphic, please be sure to include a framing chart so that the post department knows exactly how to frame it in post:



Note that circles, which guarantee that the desqueeze isn't distorting a circular pattern in any way. That way, we can guarantee what you saw on set will be exactly what you see in final color. Without the chart, we have to guess.

In this instance the distortion isn't really in question, though. It appears to be a scaling issue. The 2.39 extract should be about 20% larger than the final output. But, the image is about 40% smaller than the final output. Regardless of the desqueeze accuracy, there should be no letterbox top/bottom. The image should be edge-to-edge vertically and this dimension is unaffected by the scope. The vignette is a mattebox issue, which needs to be addressed physically, but is also unrelated to the scaling. I agree that a framing chart would help, I'll see If I can shoot one tomorrow.

I had the same issue. Using the Moment 1.55x anamorphic lens on my iPhone 16 pro max, I wanted to output video to a 2:39:1 aspect ratio, to go with other anamorphic footage shot on my Lumix s5iiX. I was filming using the Blackmagic Camera app, with the 1.55x anamorphic de-squeeze turned on. Knowing the 4k resolution on the iPhone was 3840x2160, the math to get this to de-squeeze out to a 2:39:1 aspect ratio (3840x1600) - I thought I just needed to scale the horizontal to 114.9% and the vertical down to 74.1% (or as it is in DaVinci Resolve - H zoom: 1.149 and V zoom: 0.741). Doing this should have resulted in the perfect vertical height with some room on the horizontal to crop out as needed for the 2:39:1 final output. However, the footage was too short vertically with black bars.

The only way I could get the expected footage was to film on my iPhone in the Blackmagic Camera app with the de-squeeze option unchecked. Of course, filming in this way using the Moment 1.55x anamorphic lens had the squashed image on screen - so it is not an ideal way to film. However, when I imported that (un-de-squeezed) footage into Resolve, then de-squeezed (H zoom: 1.149 and V zoom: 0.741) - I got the expected result - perfect vertical with some room to play with on the horizontal for a 2:39:1 final output.

Conclusion - Blackmagic Camera app does something fishy when it 'bakes in the de-squeeze' - we really need to have the option in the Blackmagic Camera App - to have an option for the de-squeeze to be 'PREVIEW ONLY'. It would be great to have this option for this reason - not to bake in the problematic de-squeeze.