Magenta highlights, balancing the green channel

[Hrvoje Simic]

So my question is, might it make sense to leave an optical magenta filter on camera at all times?

No.

If a magenta filter is available that equates to -27.5 tint, it should bring the green channel back down to where it should be relative to blue and red, possibly increasing dynamic range by preventing the green channel from clipping early.

The issue is related to highlights and this would affect a whole range.

It would also allow us to correct those magenta highlights in camera and see the corrected images while monitoring and even record corrected images requiring less work in post.

I don't think you'd see correct images or that it would require less work in post.
It could very easily require more.

Would a magenta optical filter affect the image in more than just the green channel in such a way that it would not properly compensate for using the tint/gain setting to balance the white clip point of the channels? Where in my assumptions have I gone wrong?

By not making a distinction between:

- Color manipulation through balancing captured color information (apart from clipped highs)

and

- Color manipulation by limiting one channel through a filter. Which is reduction of captured color information.

You cannot compensate in post for something which is not there.
At least not without penalties.

If using tint or green gain to compensate for color casts screws up colorimetry should we not be using it to correct for green or magenta spikes in fluorescent or led lighting? Or are there complexities in a magenta optical filter that I am not taking into account? Thanks to anyone who can help shed further light on this issue.

Correcting color casts works because whole range is affected, unlike this example.

 

[Mike P.]

Unfortunately even now years later I still see strange looking magenta highlights in movies/commercials/music videos all the time and know that they were shot on RED. Perhaps it's too much to assume even bigger budgets will fix their magenta highlights with DRX or grading? I still don't really understand why the camera is designed to render white as pink such that all footage has to be fixed in post if clipping is not completely avoided.

This. Also, the fact that a thread like this gets bumped years later is kind of troubling.

It's haggard, actually. REDrocket debayer didn't have DRX enabled for the longest time, so I'm assuming higher budget stuff just didn't have an alternative (though you'd think the colourist would have taken steps to avoid that fail).

Not helping is that DRX seems to just clip the highlights sooner -- that is to say, it doesn't stretch the green channel highs to match the red and blue, it merely reduces the blue & red channels down so the RGB tops are even. Not that the detail in the blue and red channel highs is significant, but it would help soften the clip (even if it's just by a bit). In that respect, it's almost better to desaturate the highlights, rather than use DRX, but that involves even more tweaking/time/money.

That said, even though DRX certainly seems like a band-aid to an issue that shouldn't have been there to begin with, seeing pink in the highs of "professionally finished" footage is far more aggravating.

 

[Marc Wielage]

That said, even though DRX certainly seems like a band-aid to an issue that shouldn't have been there to begin with, seeing pink in the highs of "professionally finished" footage is far more aggravating.

I will again say that fixing a slight pink tint in highlights is very, very trivial to do for any decent colorist. Pull a highlight key and desaturate... problem solved. Even film did not always clip as pure white -- though this is also partly the problem of films scanners.

 

[Mike P.]

Haha, you don't need to tell me how easy it is Marc... That's why I said it's more aggravating seeing pink-highs in broadcast material, even if it's something that probably shouldn't've been an issue to begin with.

All I'm saying is putting DRX to full and applying it to "all clips" before transcoding (or importing, for that matter), is a pretty easy/fast solution (though not as good as pulling a key and desaturating). Which is what makes seeing it nowadays (certainly since DSMC) kind of haggard.

 

[Marc Wielage]

Haha, you don't need to tell me how easy it is Marc... That's why I said it's more aggravating seeing pink-highs in broadcast material, even if it's something that probably shouldn't've been an issue to begin with.

I can't recall ever seeing a broadcast show or commercial like this. I have gotten in material that had lopsided whites (including film), and we just fixed it as a matter of course. High on my list of pet peeves is contaminated clipped whites in headlights, bare lightbulbs, or other light sources... unless the DP has a specific reason not to want it pure white.

What is true is that different CCD and CMOS pickups react differently to overload. I've also seen them "bend" the image differently when you really stress them out with 4 or 5 stops of overexposure, which leads to weird, non-linear problems. In TV shows, I generally recommend to DPs that they put the practicals on dimmers so they can knock them down another 10-20% to avoid any extreme overload problems, especially in high contrast situations. But it's the DP's call on whether he agrees or not.

I had a case on a pilot awhile back where we had a non-dimmable neon sign in the background of a bar, and that was clearly about 2 stops overexposed compared to everything else. Even there, I was able to grab it in the final and bring it down to the point where some color came back and it didn't distract from the actors in the foreground, so that was an easily-solvable problem.