Purple Problem?

N

north45co

Member
Hey all,

I was asked to film a party a couple weekends ago. The party had a bunch of different colored lights. While I was filming I noticed that the purples ruined the image, but it only happened during the purples (or dark blues). Whats the deal? How can I prevent it for the future, and can I fix it in post?

sloan1.jpg


sloan2.jpg


I know they are moving, but that isnt the problem (it happened when they were standing too).

Thanks,

Ian
 
Ruined wasn't exactly the right word, sorry.

The majority of the edges are pixelated... the hair, the arms, etc

(like the shadow on the girl's arms in the second picture).

but it only occurs when there is purple on the screen. (it looks a lot worse in motion)
 
It was the factory settings for f6 or f5, I don't remember which I shot with.

Is it just that the chip dpes not handle flourescent purple well? Kind of like reds?
 
Exactly like reds. It doesn't handle blues well either, and purple is red+blue.

Color is sampled at 1/4 the resolution of luminance (brightness). And brightness is primarily made from the green CCD. So if you only have red in your shot, or only have blue, then the green chip can't do its job and that means you pretty much only get about 1/4 the resolution(!) Which is what you're seeing. Soft, fuzzy purple imagery.

This problem would plague any DV or HDV camcorder. You'd need something with higher color sampling (4:2:2) in order to not see the issue anymore.
 
Barry I totally understand the logic of what your saying and it makes complete sense to me, though why am I not seeing this on he A1? Is it just the higher res?
 
You should see the exact same effect on the A1 at full native res. But if you're downconverting to SD it'll average the shots together and deliver full res again.

Shoot a scene under blue or purple lighting, and the exact same scene under normal lighting, and the normal-lit scene should be much sharper.
 
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