Purple Sun Woes-

[Ryan E. Walters]

I am hoping that maybe someone here can shed some light on this issue- and maybe I'm just stuck and this is what it is ...

Is there a way to get around the purple sun issue?

I find it frustrating that a camera such as the Red One cannot just let clipped highlights go completely clipped. Or that it can't figure out the extreme clipping and then set that value to white instead of assigning it to purple. With all of the other digital formats I've used this has never been an issue- but it is a frustrating one to say the least.

I was out shooting some stock footage the other day and I wanted the sky to be mostly blown out and I wanted to keep my subject well exposed. Additionally, there were times when I wanted my subject to cross over the sun and get some fun flare action happening. I was very happy with the results that I go, and the footage looked great. It wasn't until I got back to edit and grade the footage that I realized what a pain it would be to remove the purple dot!

Each clip had it's own set of difficulties depending on how much crossing of the sun went on. For this particular clip I had to create 10 separate secondary rooms to track the sun and then use a selective mask / vignette to pull the gain (highlights) up to overexposure range. Since I am only allowed 8 secondaries I had to create an additional grade. Further more, I had to create the base grade that had not sun correction on it and then use only the parts of the clips that had the actual matte on it. Otherwise little bright circles would be left in areas when the matte was not traveling.

This should not be THIS complicated...
The Color Grade for one of the clips:

The FCP Timeline for the same clip:

Now I realize that part of the problem is how Color can (or cannot in this case) track moving objects as they go behind other objects. But the bigger issue is that I should not have to be dealing with this in the first place...

So, am I stuck, and it is what it is- or did I do something incorrectly in camera?

 

[brandon thomas]

can't you pull a selective key of just the purple dot sun, and hand track that inside a vignette?

if i'm not mistaken, you should be able to blow it out in one secondary..

 

[Ryan E. Walters]

Thanks for the suggestion / input.

Unfortunately I was not able to do that in Color to get the best results. By selecting the dot I would either end up selecting some of the purple in the sky, or if I could just get the dot, I was never able to get the value up high enough to make it completely blow out.

The only way I could get it to completely blow out was to track it with a vignette ...

 

[Joshua Brown]

Thanks for the suggestion / input.

Unfortunately I was not able to do that in Color to get the best results. By selecting the dot I would either end up selecting some of the purple in the sky, or if I could just get the dot, I was never able to get the value up high enough to make it completely blow out.

The only way I could get it to completely blow out was to track it with a vignette ...

I don't know about the camera issues, or the limitations of Color in how it reads the data. HOWEVER, I believe if you just do a HSL key and mask it with a vignette, you should be good. I can't see your clip so I don't know how hard it would be to track your sun as it passes your subject. But a combination of auto/manual/auto tracking for when the sun is visible/hidden/visible should work.

-J.A. Brown

 

[Ryan E. Walters]

Hmmm- combining the two methods might be able to cut down on the number of rooms in use- I'll give it a try.

(I still think this should be a non-issue...)

 

[Joshua Brown]

Hmmm- combining the two methods might be able to cut down on the number of rooms in use- I'll give it a try.

(I still think this should be a non-issue...)

Agreed on both counts.

- J.A. Brown

 

[Ryan E. Walters]

The purple sun solution!

The purple sun solution!

So I stumbled upon the solution to the purple sun:

http://www.ryanewalters.com/page2/files/Purple_Sun_Solution.html

The Purple Sun Quick Fix:
1. Do not use the direct R3D’s in Color.
2. Render out in your preferred codec. (I chose ProRes HQ in this example)
3. Make sure to set the color space to Camera RGB and Gamma Space to REDlog.
4. Adjust the highlights until the purple sun blows out to white. (It should not take a lot of adjustment.)

 

[Brandon Kraemer]

So I am curious to know the root cause of this purple sun phenomena, we recently did post on a shoot shot with the SI-2K and this was a real issue. Our solution was similar to the workflow just discussed, making a LOG space transcode.

Is this caused by an echo on the sensor or just some kind of clipping issue?

 

[Jeff Kilgroe]

Black / Purple sun is an artifact of the photosites on the sensor becoming over-charged. Essentially, they are overloaded due to extreme exposure. It's really a CMOS thing and not a RED One thing. Many other CMOS cameras exhibit the same issue...

Here's a sunset shot with the iQeye 1K IP surveillance camera.

Sensor charge data is analog in nature and it's difficult to determine at the RAW data level whether or not there is black sun clipping going on. However, it's simple enough to process out in post. I'd like to think that upcoming RED tools like REDCINE-X would have the ability to mask out the effect. As Ryan suggests above, it can often be adjusted out of the image. I can typically adjust it right out of the image within Red Alert or elsewhere, direct from the R3Ds or not. It's actually easier direct from the RAW files. I've also got a lot better about knowing when a highlight is going to go black and dealing with it preemptively when I shoot.