Purple fringes in tele/zooming in! What is this??

Thanks.

I´m not sure if this applies to my purple issue, because it is not all over the picture, but just in the lower left corner and a little bit on the right.

I have to do more testing, but I guess it is chromatic aberration.


Still, the above mentioned magenta issue should be dealt with anyway.
What is being supposed though: A magenta coloured filter is needed when shooting highlighted pictures with a lot of contrast?

What exact filter should be used?
Where do I get it?
 
Phew, that felt like having a tooth pulled.

yes this does apply to high contrast images. see the movie clip link at the bottom, and how much more detail is bought in aswell as channels are balanced.

This is basically a video limitation that you just don't see with digital film such as Cineon files, where the RGB all track together up to pure white, rather than being clipped - dynamic range.
 
Well as a quick fix, for most shots you could just dial down saturation in magenta, since it's otherwise such an unnatural color.

If I had a magenta filter, I'd experiment just to see what happens, but I think I know enough about the cam now to avoid this or fix it in post if necessary.
 
Looks to me like it might be slightly over exposed which is going to accent purple fringing.

I'm not seeing that much to be honest with you. I think if you dialed down your exposure a touch on that shot it would be much less noticeable.

late,r
Jason
 
Hey guys,

I found this thread by chance...

My little "spiel" about my magenta filtering technique (exotic - yes) really doesn't apply too much to "purple" fringing. It's about magenta highlights, meaning, a whole cloud in some wide shot of a landscape looking very purple for example, or a blown out table lamp, etc...

It's an issue with WB, channel gain, and uncompressed recording. You'll never see it in a consumer camera (or any non RAW camera for that matter), they make sure you never do. Even Red One can have this issue from time to time.

There are two types of CA, and you never hear this, so I'll go ahead and explain...

Lateral CA:

This is when channels are not lined up properly across the frame. Basically, the channels are a little warped, thus you get the funky colored edges from time to time, mostly apparent on high contrast edges. This is what everyone talks about.

And for the one no one ever cares to mention...

Longitudinal CA:

This happens when a channel is OUT OF FOCUS. Yep, you read it right, an out of focus channel, or rather, a channel with focus set either in front of or behind the sensors plane. One channels could be tac sharp, usually its the green channel, but the blue could be very soft, and the red somewhere in between. When this happens, edges bloom, or appear to expand. This can also cause the fringing you see.

You CAN correct this to some degree though.

Take the problem shot into After Effects. duplicate the shot three times. On each layer, put a curves effect. Eliminate two channels for each layer, leaving only one channel left. Apply "Screen" blending mode to each channel. Make each layer one channel, one for just Red, one for just blue, and one for just green.

Now you can shift the the channels around and correct the edges. I recommend using Green as your base channel for lining things up. I also recommend using the corner pin tool to help warp channels around a bit.

Problem solved, or at least drastically minimized. I do this with lots of my Andromeda footage, especially nature shots outside.
 
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