Welcome to our community

Be a part of something great, join today!

Log in
  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Purple Outline?

P

Phan Tran

Well-known member
Joined
Apr 17, 2007
Messages
54
Reaction score
0
Points
0
I know of the purple/black sun issue, but this is the first time I've seen this with my camera. Actor is sitting in front of a window. Spot meter on his face is f2.8 @iso 320. The widow was reading f45.

We powered down and I suggested the DP put some ND on the window, bring up some of the lights on the subject, and stop down to reduce the range. It helped, but there was still a touch of purple outlining since he didn't want to change too much of his setup.

Has anyone experienced this?

Build 15 v2.2.5

Phan
 
Yup,

They put ND on the window. The purple/black sun I can kind of understand. But DP was not happy seeing what looks like a less than elegant way of handling a high contrast situation.

Phan
 
What lenses were you using?

This looks like strong chromatic aberration - very noticeable with blown out or really high contrast edges on longer lenses. I've seen this happen on DSLRs with their chromatic aberration compensation algorithms turned off.
 
Hi Kenn,

We're using Arri Ultra Primes T/1.9 from Clairmont. It was an 85mm on that shot. Has anyone else experienced this with some of the other long Arri Ultra lenses?

Phan
 
Hmmm... I see you're on Build 15 so you wouldn't be processing in Redspace, which with it's stronger S-Curve and color saturation accentuates the color fringing...

That's a tough one ptran. Maybe we can get Graeme in on this conversation as there's possibly some processing stuff that can happen on the codec end to help eliminate the fringes on extreme high-contrast edges.
 
It's your lens. Most lenses do that wide open, or close to wide open.

Graeme
 
Yeah that was fast.

It was an 85mm T1.9 lense. They had it on T2.0 for the shot I attached. They lowered the lighting contrast and then stopped down to T2.0/2.8 for the shot which did improve it.

Graeme, what is the science/physics of what is going on in layman's term?

Thanks again for such a quick answer.

Phan
 
this is a little disturbing that its the "lenses" and it happens all the time if one is shooting near wide open? 2/2.8 is 3.2 and the lense is a 1.9 thats where most DP's like to live.
 
I guess it is chromatic aberration, which is present to some degree in all lenses (although some are so good that you can't see it without extreme magnification). Notice how this happens near the edge of the frame. Chromatic abberation is worst at the corners and outer edges of the frame, and should be zero at the exact center of the frame (if the lens is properly concentric). You can tell for sure in this particular situation if you just pan the camera right so the subject's profile against the backlight is dead center. If the purple color was due to chromatic abberation, the fringe should disappear entirely. If it does not disappear when centered, it must be something else, at that point you can begin blaming other parts of the system.

Another telltale sign of chromatic aberration is that the color will change (for example, to green) if the high-contrast feature moves past center to the other side of the frame, or the bright-dark edge is reversed right-to-left on the same side.
 
It's a form of chromatic aberation. If you do a Google on "purple fringing" you'll learn about it. I've seen it in pretty much every lens I've used.

Graeme
 
Graeme,

Is this Chromatic aberration only a digital thing? I used my canon lenses with my 35mm film camera and never noticed this pink aberration until I bought my 20D and then I've got a lot of pink and green on high contrast scenarios. I thought it was only a digital thing but I guess I was wrong.

Thanks for the info anyway.
 
Chromatic aberration is definitely a property of the lens. Specifically, the lens has a slightly different focal length for red, green, and blue colors. This causes color fringing on high-contrast edges towards the outside of the frame, where the separate colors from a white scene feature do not perfectly align to form white in the image plane.

That said- film has its own set of distortions; for example it may desaturate colors near overexposed regions, which tends to hide some amount of chromatic aberration.

Note: if you have a strong white-black-white pattern like a dark tree branch silhouetted against a bright sky, chromatic aberration will cause different colors to appear on either side of the feature. For example, a purple fringe on one side of the branch and green on the opposite side. If you've got purple showing on both sides, you've got some other problem, which might be related to the sensor.
 
jbeale said:
That said- film has its own set of distortions; for example it may desaturate colors near overexposed regions, which tends to hide some amount of chromatic aberration.
.
Click to expand...

Not to be picky, but would be safe to say that in Film, chromatic aberration is less noticeable because of some desaturation of colors near overexposed regions, the way film handles highlights and maybe also film grain?.

I wonder if there is a filter in AE or another program to fix or at least attenuate the color aberration like in photoshop CS3. I have to say that I haven't seen that bad aberration as that pink line in the actors face. And my lenses are not that good, so I am getting ready for some nice pink and green color bands.. :blush:
 
Was watching some old TV from the 70s, shot on film. Shot was similar to this one, with a very bright window behind the character. All along the edge of the window was a purple fringe.... So it's not just digital that gets this effect, but film too.

Graeme
 
Sorry Graeme, I don't agree. I have seen this purple fringing a lot during shooting with my Red, and it is either a combination of the purple OLPF flare or the "purple sun" next to an object which is not as heavy overexposed as the spot where the flare occurs. I saw it happening while on a dolly slowly exposing a strong highlight and before the "purple sun" appeared; a small purple highlight came up. So yes, I do think it is specific Red and the only solution is bringing back those highlight. Overall I love the camera, I just finished my 50th shooting day on my Red today......


Mick van Rossum NSC
 
It's certainly not RED specific - every DSLR I've owned, every one I've played with does this purple fringe. I've seen it on stuff shot on film. It's primarily a lens artifacts, which can be proven as the one thing that effects the appearance of the purple fringe is the aperture of the lens.

Graeme
 
Hi Mick,

It's not related to purple/pink sun as that's a function of something completely different. Purple fringing is related more to specific lens designs and their effect is similar but varied on film, single sensor, and digital.

BTW, any relation to Guido van Rossum?
 
You must log in or register to reply here.
Back
Top