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Magenta Tint

PostPosted: Mon Mar 05, 2018 11:49 am
by James McDonagh
Hey guys,

Check out this clip and go to 18 seconds in and look at the rim of the brown horses's nose. This is some footage I got with my URSA Mini Pro. There is a magenta tinge there which is a lot more noticeable in the uncompressed file as opposed to YouTube's compressed version. I have specifically noticed this when using the built in ND filters and when I aim the camera at a bright sky, but now with this clip it seems to show that the magenta can pop up at any time. What gives? And what can I do about it other than spam green through the image in post?

I'm guessing this is why a "10 tint" setting is the default option that is set on the URSA Mini Pro and was used during the commercial Blackmagic produced for the camera.

Many thanks,
James


Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 4:15 pm
by roger.magnusson
I haven't checked with scopes, but it looks like one or more RGB channels clipped since the highlights are overexposed.

Regarding +10 tint, more info here. But the values may need to be changed to calibrate your particular camera.

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 5:17 pm
by James McDonagh
roger.magnusson wrote:I haven't checked with scopes, but it looks like one or more RGB channels clipped since the highlights are overexposed.

Regarding +10 tint, more info here. But the values may need to be changed to calibrate your particular camera.


Hi Roger thanks for your reply. I do not think this has anything to do with overexposure as Im reviewing my footage that I took while at a park which was covered in a blanket of snow and none of the shots are overexposed yet there is the appearance of a magenta tint in the sky and all around the silhouttes of the people in the park.

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 5:25 pm
by Kyle Gordon
That magenta edging is called chromatic aberration, and it's an artifact of the lens, not the camera.

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 5:43 pm
by James McDonagh
Kyle Gordon wrote:That magenta edging is called chromatic aberration, and it's an artifact of the lens, not the camera.


I see. Thank you very much for the clarification. Do you have any advice on how to counter it on set or in post or are all lens artifacts pretty much final?

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 6:11 pm
by Keith Babineaux
James McDonagh wrote:
Kyle Gordon wrote:That magenta edging is called chromatic aberration, and it's an artifact of the lens, not the camera.


I see. Thank you very much for the clarification. Do you have any advice on how to counter it on set or in post or are all lens artifacts pretty much final?


CA on lens is final. You can't fix it in post. You'll have to use different lens. Which lens is that? I'll make sure to avoid it in the future.

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 6:13 pm
by James McDonagh
Keith Babineaux wrote:
James McDonagh wrote:
Kyle Gordon wrote:That magenta edging is called chromatic aberration, and it's an artifact of the lens, not the camera.


I see. Thank you very much for the clarification. Do you have any advice on how to counter it on set or in post or are all lens artifacts pretty much final?


CA on lens is final. You can't fix it in post. You'll have to use different lens. Which lens is that? I'll make sure to avoid it in the future.


rokinon cine lenses

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 6:37 pm
by roger.magnusson
Oh, I'm talking about another artefact, sorry. I couldn't watch anything else after seeing it. :)

Horse R239, G255, B255.jpg
Horse R239, G255, B255.jpg (99.4 KiB) Viewed 720 times

The white horse is cyan because the green and blue channels are clipped. RGB values 239,255,255

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 7:27 pm
by James McDonagh
roger.magnusson wrote:Oh, I'm talking about another artefact, sorry. I couldn't watch anything else after seeing it. :)

Horse R239, G255, B255.jpg

The white horse is cyan because the green and blue channels are clipped. RGB values 239,255,255


Oh wow, thank you! That makes sense... so basically it's because of too much light flooding the sensor? That makes a lot of sense, thank you.

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 7:35 pm
by Earl R. Thurston
James McDonagh wrote:... so basically it's because of too much light flooding the sensor?

Or possibly the colour correction, grading or LUT mapped this area into overexposure. If this was shot RAW it's possible there is more sensor data available for highlight recovery than was used in this output.

Re: Magenta Tint

PostPosted: Mon Mar 05, 2018 9:56 pm
by Uli Plank
Since we are using Bayer patterns in our sensors, it's quite possible to saturate one group of photo cells and not the others if any color has much more energy than the rest. Remember the infamous pink highlights?

Re: Magenta Tint

PostPosted: Thu Mar 08, 2018 9:28 pm
by Ric Murray
James,

Not trying to haunt you here, but this goes back to the other thread "Cinematography Case Study". Once the sensor gets flooded or clipping occurs all kinds of things go off the rails. Simple solution is to use the histogram and expose for the highlights, light (or fill) for the shadows, and adjust the Gamma in software, either Premiere or Resolve or anything else you like. The LCD is there for composition & framing, It's not a calibrated monitor.

Re: Magenta Tint

PostPosted: Thu Mar 08, 2018 10:46 pm
by James McDonagh
Ric Murray wrote:James,

Not trying to haunt you here, but this goes back to the other thread "Cinematography Case Study". Once the sensor gets flooded or clipping occurs all kinds of things go off the rails. Simple solution is to use the histogram and expose for the highlights, light (or fill) for the shadows, and adjust the Gamma in software, either Premiere or Resolve or anything else you like. The LCD is there for composition & framing, It's not a calibrated monitor.


Hi Ric,

Don't worry about haunting me I sincerely appreciate all the feedback and help! Thank you for your input. As you could see on this thread some people thought that the magenta was an artifact from the lens and not a product of overexposure. I'm glad to hear everyone's opinons and thoughts thank you :)

Re: Magenta Tint

PostPosted: Fri Mar 09, 2018 5:22 pm
by Kyle Gordon
It depends what you're talking about.

The purple fringe on the brown horses nose where it meets with the white behind it is chromatic aberration from the lens. The cyan tint of the white horse behind is color channels clipping.