Blackmagic Forum

I have some footage in which a 0.9 neutral density filter was used during shooting. Now the skies look great but the rest of the image is way too dark.
What's the best way to correct for that?
Is it possible that details got lost into the shadows?

Thank you for your help !

It's possible the detail on the rest of the image was lost. Check the scopes and see.

A good neutral density filter is supposed to be, well eh, neutral. So a good filter by itself would not need color correcting. However variable neutral density filters are often a problem when it comes to color fidelity.

But it seems the footage was underexposed. Try to increase the gain.

Maybe the classic 'screen blend' method for underexposure correction ? Layer Node with Composite Mode > Screen and opacity (Key Output Gain) adjusted as required.

Or else, using the 'Shad' control (#2 panel under the Primary Wheels), see how far you can lift the shadows to recover detail before noise becomes conspicuous, and then (positively) adjust Gamma as needed. If you start losing highlight detail, try applying a little highlight pulldown (using the 'HL' control) balanced with Gain - don't want to end up too flat. And maybe a touch of Mid-Tone Detail (local contrast) to help it along.

Or a power window. Hardly a wide exterior goes by on which I'm not inclined to throw a tracking power window on just the sky, then I grade the ground differently. Sometimes I'll throw a little more blue into the sky if the scene warrants it. In the real world, there's often several stops of difference between the two, so it's a tough exposure to balance without a window.

Marc Wielage wrote:Or a power window.

Yes, might be the best/only recourse if the above methods end up losing sky (cloud) definition.

Obviously, if conspicuous noise is an unavoidable by-product of the 'exposure correction', you are going to have to deal with that as best. Excluding the sky with a power window and/or using a luminance qualifier (key) would at least enable you apply the NR selectively. Maybe also (partially) desaturate the shadows as a final step.

In really tough situations, I took a cue from Warren Eagles and actually put two copies of the camera files on adjacent video tracks in the timeline and used radically-different Raw settings -- one optimized for the dark scenes, one for the overexposed sky. Once that was done, I figured out a way to cut a hole with power window used as an alpha, and basically got "poor man's HDRx" out of it. This can work extremely well as long as you don't have any actors cross the boundary between layers (or at least the dividing line of the window).

Marc Wielage wrote:In really tough situations, I took a cue from Warren Eagles and actually put two copies of the camera files on adjacent video tracks in the timeline and used radically-different Raw settings -- one optimized for the dark scenes, one for the overexposed sky. Once that was done, I figured out a way to cut a hole with power window used as an alpha, and basically got "poor man's HDRx" out of it. This can work extremely well as long as you don't have any actors cross the boundary between layers (or at least the dividing line of the window).

There is little reasons in doing that: either you have information or you don't. "Different raw settings" is just a multiplication in linear light of the raw data.

You will get the same result in debayer and just power window.

Thank you very much for all your helpful replies !

Right now, I'm in the middle of prepping for a video shoot, so I don't have much time in front of my laptop.
But once the shoot is over, I'll delve more into it.

Best from Victor.

Victor van Dijk wrote:What's the best way to correct for that?

Shoot in a Log profile, which generally increases the recorded Dynamic Range.

Marc Wielage wrote:In really tough situations, I took a cue from Warren Eagles and actually put two copies of the camera files on adjacent video tracks in the timeline and used radically-different Raw settings -- one optimized for the dark scenes, one for the overexposed sky. Once that was done, I figured out a way to cut a hole with power window used as an alpha, and basically got "poor man's HDRx" out of it.

I don't work with Raw but I take (what amounts to) a similar tack for salvaging (as best) over-exposed or heavily backlit footage. First apply a 'multiply blend' (at adjusted opacity) to pull-down what near-blown detail is possible from the highlights. Pretty aggressive, but pulldown using the 'HL' is usually not enough in such cases. Sometimes I'll split the luma and chroma and apply the 'multiply blend' to the luma only - can make it easier to control saturation levels subsequently. Then a massive shadows lift using the 'Shad' tool (sometimes two passes if 100% is not enough) and readjustment of the black-point as needed. Of course there's usually noise to deal with, but the results are generally pretty good.

Toned back and with boosted 'mid-tone detail' it can also produce a rather nice 'pseudo HDR' look. I've used it coupled with a KodakTRI-X400 emulation LUT, grain and antique silver overlay to create an intense, gritty B&W 'Silvertonish' effect.

Could be done with RGB curves of course - just variations on a negative S-curve, but more finicky to get right.

waltervolpatto wrote:There is little reasons in doing that: either you have information or you don't. "Different raw settings" is just a multiplication in linear light of the raw data.

You would think, but the main feature had an ISO at 1200 and the portion I was trying to salvage had to be cranked down to 300. If I did it with the traditional Resolve controls, we were bending and stretching the picture to the point where the seams showed too much. With the Raw, the horizon seemed to be a little cleaner and we got something approaching clouds.

I agree, 99% of the time, I can get there the conventional way with the controls we always use. I'm always willing to experiment if it gives me one more option I haven't considered yet. If it's just one shot out of thousands, it's not a big deal to me; I just say, "hey, that looks great!" and move on.