Question about color resolution

[Rodrigo]

Just wondering: let's say I need a keying done for a SD tv show.

Is there any chance to shoot with the pana HVX200 in 1080p and afterwards scale down the pic to 16:9 SD doubling the color resolution? I mean, by downscaling the image I would lose luma samples but I would like to know is if there is a way of keeping all the chroma resolution so that at the end I would get an anamorphic SD 4:4:4 picture, perfect for keying in combustion, for example.

Would it be as simple as using a codec for that SD render that would accept 4:4:4?

I apologize in advance for my poor english.

[David G. Smith]

From the posted specs, the HVX shoots in DVC-Pro50, which is a standard definition format with 50mbs/sec biterate and 4:2:2 color sampling and lower compression. This may prove to be the best way to use the HVX for SD chroma key compositing.

[araujofh]

Hey David,

What if you shoot 1080p, then crop it rather than downsample. Wouldn't that give better results? Obviously, you would have to frame for SD when shooting, but wouldn't that give nice wide shots? I guess Barry suggested this a while ago, not quite sure. Please Barry, correct me if I am wrong.

[Jim Arthurs]

I think a number of people have suggested doing this, including me. I've done exactly this, but using HDCAM.

See vol. 6, issue 4 of HighDef magazine for an article I wrote about a greenscreen shoot and virtual sets. Another advantage to your original footage being in HD is that you can pan/scan and zoom into the footage to some degree with less quality loss.

1080p would have more compression than the SD equiv., but this is diminished by the larger starting image (in proportion to the fixed sized artifacts) and the effect of quality downsampling.

"Effective" color space would be improved as well by the downsampling, giving you nearly 4:4:4 color.

Downside would be working with bandwidth demanding HD if you're only set up for SD, but worth it IMO.

Regards,

Jim Arthurs

[Jim Arthurs]

Hey David,

What if you shoot 1080p, then crop it rather than downsample. Wouldn't that give better results? Obviously, you would have to frame for SD when shooting, but wouldn't that give nice wide shots? I guess Barry suggested this a while ago, not quite sure. Please Barry, correct me if I am wrong.

I didn't read this carefully, no, cropping HD to SD won't give you better results than downsampling HD to SD. In fact, cropping to exactly SD size will probably look a lot worse than just shooting SD. The image won't be as sharp because you're using a smaller area of the lens FOV for one thing, also the crop will show the increased compression at 1:1 which will suffer when compared to the lighter compression of DVCpro50...

Regards,

Jim A.

[Spiff_2]

In fact, cropping to exactly SD size will probably look a lot worse than just shooting SD

On DVCPRO-HD, you can expect the perceived quality of an image cropped this way to be equal to miniDV. Chroma sampling will be slightly improved, but mosquito noise and intra-frame compression artefacts will be more visible.

To DVD, it DVCPRO-HD will probably look better though - given you'll be taking 4:2:2 to 4:2:0 as opposed to 4:1:1 to 4:2:0 (where you get closer to 4:1:0). Note however that the pixel aspects are different, so this mapping won't be quite as good as you could hope for.

-Spiff

[araujofh]

I didn't read this carefully, no, cropping HD to SD won't give you better results than downsampling HD to SD. In fact, cropping to exactly SD size will probably look a lot worse than just shooting SD. The image won't be as sharp because you're using a smaller area of the lens FOV for one thing, also the crop will show the increased compression at 1:1 which will suffer when compared to the lighter compression of DVCpro50...

Regards,

Jim A.

Hi Jim,

Thanks for clarifying this.