HDV keying shooting tips
 

This weekend I began to do some green/blue screen tests with my FX1, and I thought I'd report some of the results here.

My tips so far are the following:

- Set shaprness to 0. Sharpness enhances edges. This is bad news for getting accurate keys and leaves bizarre little halos. It also makes the image have higher bandwidth and is harder on the compressor.

- Despite the "clean" gain of the FX1, you are best to shoot at 0 dB. This means buying more lights in my case, or shooting in the daytime using the ambient light in my apartment (horse).

- If you are shooting a scene with minimal fast motion, go ahead and shoot 1080i. It will maximize the resolution of the camera, and give the sharpest image.

- If you are shooting a scene with a lot of motion (i.e., martial arts) you are better off just shooting in a CF mode. When there is a lot of motion a lot of the image will get deinterlaced anyway for any real FX work, and the decreased luma resolution will ease up on the compressor, giving you higher fidelity in the blurred regions with less macro-blocking.

Here are the test images I've got:
http://s38.yousendit.com/d.aspx?id=3...Q0C16D7SBN0I7E (~20 MB)
- all shots with exception to the horse were shot at +9 dB gain, sharpness 8
- the horse was shot at 1080i, 0 dB, sharpness 0

-Steve

I've gotten rather good results with more or less all sharpness settings between 0 and 8, depending on the scene - but it's required a bit of post production trickery ;-)

That seems like it's worth experimenting for sure!

Here's more tips:

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Technically green should be much better than blue, see this test i made:

http://www.kolumbus.fi/erkki.halkka/...nd_keying.html

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Cineform codec is great - for everything except blue/greenscreen. On my tests, i got much better results using uncompressed. It might very well be that half of the compression problems here are not mpg2, but rather cineform problems.

Edit: the cineform problems are especially visible in fast motion, field based footage. It seems to mush the color in some frame-based way.

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One thing that makes fast motion show MUCH less compression problems is using i.e. reel smart motion blur at moderate settings. This blends the blocks, giving a lot better key.

Hi Eric,

At the request of a friend, I shot some more test images this morning, both at 1080i and CF30 with 0dB gain. I did frame-by-frame comparisons with Cineform (Large, interlaced/progressive compressed, AspectHD 3.3) and the M2T files, and these are the ONLY things I noticed:

- The Cineform algorithms for 4:2:0 chroma-deartifacting increased the quality of the key around sharp edges.
- There is a slight colour-shift in the Cineform images, as I suspect After Effects and HDLink handle the YUV.7xx colourspace differenetly.

In interlaced frames with heavy macro-blocking I noticed no difference except these with the Cineform intermediate. On what version of Cineform did you perform your tests?

I would also re-affirm my opinion that the CF modes key better in heavy motion situations than the interlaced frames, and exhibit considerably less macroblocking.

Here are the new tests, all shot 0 dB, 0 sharpness. Note: the bottom left corner of the screen looks darker. This is a shadow of the toy, so consider that something to keep as a real shadow on the background if the background is close, and something to remove if the background is far away.

http://s37.yousendit.com/d.aspx?id=3...Z2YICTYH29MC1L

-Steve

Hello Steven

Please can you re post the link above i just went there but it has gone.

This contradicts my own experience when both M2T>Uncompressed>AE Key and M2T>Cineform AHD Large>AE Key produced same results.

In my humble opinion, Cineform AHD at Large setting is just as good for bluescreen keying as uncompressed AVI (derived from m2t mpeg).