4k HD vs 4k 2.1

anthony derose · November 27, 2009

Shooting a student thesis with the Red Camera coming up. We want to have a anamorphic feel but since we are outputting to HDCam and will probably only finish on HD 4K HD seems the best way of going about. Would being the best way to achieve that widescreen look be setting frame guides for 2.40 and then cropping it in FCP?

Gus Sacks · November 27, 2009

Shooting 4k HD gives you less of a pixel count than 4k 2:1 or 4k 16:9.

4K 16:9 (4096x2304), 4K 2:1 (4096x2048), 4K HD (3840x2160), 4K ANA (2816x2304)

At the end of the day, to crop a 2.40:1 image, you'll have to lose resolution... If you're shooting spherical, I'd just shoot 4k 16:9, and just keep as much horizontal resolution as you can.

John Sprung · November 27, 2009

4K HD is exactly double the pixel counts of 1920 x 1080 HDTV, which simplifies the math for the downconversion, which should give you better results. But if your intended product is anything other than 1920 x 1080, it's the wrong tool for the job.

-- J.S.

Satsuki Murashige · November 28, 2009

Build 21 (still in Beta, I believe) has the new 4.5K format that you can use for 2.40. It uses more of the sensor horizontally, so you'll get a wider field of view with more resolution. If you're cropping 16:9 to 2.40, I don't think it's worth shooting 4KHD because you probably won't be scaling exactly 50% in post anyway, negating the only benefit of the format.

Haven't shot with Build 21 yet myself since most rental houses only run release builds on their cameras. But for a student film (not a commercial job), the risk may be worth it.

David Mullen ASC · November 28, 2009

Build 21 (still in Beta, I believe) has the new 4.5K format that you can use for 2.40. It uses more of the sensor horizontally, so you'll get a wider field of view with more resolution. If you're cropping 16:9 to 2.40, I don't think it's worth shooting 4KHD because you probably won't be scaling exactly 50% in post anyway, negating the only benefit of the format.

Sure you would be. You guys have to stop thinking of this as cropping to 2.40 or losing resolution, etc. HD broadcast is 1920 x 1080. If that's what he's shooting for, then he should shoot 4K HD.

It makes absolutely no difference whether that HD version is letterboxed to 2.40 or whatever, it's still a 1920 x 1080 signal, just with black borders in the picture. So there is no resolution loss involved, not until that 2.40 area inside 1920 x 1080 is used for some other purpose than HD or SD, like a blow-up to 35mm anamorphic.

In 4K HD mode, you're converting a 3840 x 2160 RAW recording to 1920 x 1080. The letterboxing to 2.40 is incidental to that conversion and has no affect on the amount of scaling.

The only real question is if this is just for HDTV viewing, why is it being framed for 2.40, which is really best used for theatrical projection. On the other hand, it's a student project so why not make it 2.40 letterboxed...

Satsuki Murashige · December 1, 2009

It makes absolutely no difference whether that HD version is letterboxed to 2.40 or whatever, it's still a 1920 x 1080 signal, just with black borders in the picture. So there is no resolution loss involved, not until that 2.40 area inside 1920 x 1080 is used for some other purpose than HD or SD, like a blow-up to 35mm anamorphic.

Ah right, that's a good point...

The only real question is if this is just for HDTV viewing, why is it being framed for 2.40, which is really best used for theatrical projection.

I could see that being an issue if they're asked for a 1920x1080 16:9 broadcast version without a letterbox (unlikely for a student film I guess, but still). If they wanted to create a 16:9 version later and didn't protect for it, then they would have to crop into the 2.40 area to create the 16:9 version. That still would be fine resolution-wise, but it would be a lot less than a 50% scale down and thus a pain.

So if they're going to shoot 4K HD with 2.40 frame guides, then it would be smart to at least protect the whole frame and use custom frame guides with a near common top instead of the standard center cut 2.40.

John Sprung · December 2, 2009

So if they're going to shoot 4K HD with 2.40 frame guides, then it would be smart to at least protect the whole frame and use custom frame guides with a near common top instead of the standard center cut 2.40.

Indeed, they could even do a tilt-n-tweak in post, making the best possible 2.39 extraction shot by shot. We used to do that for TV back when 1.33 was the dominant frame, and we needed a secondary 1.78 extraction. You can even key frame and ramp it, making the operator look like an absolute genius on stand-ups. ;-)

(BTW, there's no such thing as 2.40. It's really 2.39 if you do the math on the aperture dimensions. It's one of those weird mistakes that's gained currency, who knows why.... )

-- J.S.

Satsuki Murashige · December 5, 2009

(BTW, there's no such thing as 2.40. It's really 2.39 if you do the math on the aperture dimensions. It's one of those weird mistakes that's gained currency, who knows why.... )

For film originated and theatrical projected projects, sure. But for digitally originated and posted (student/amateur) projects, nobody really cares. ;)

Sam Martin · January 2, 2010

For film originated and theatrical projected projects, sure. But for digitally originated and posted (student/amateur) projects, nobody really cares. ;)

I have to totally agree with you on this....