My camera changes exposure when recording - How can I undo this in shotcut?

#1

Hy, I bet my question is too simple, but I didn’t find in tutorials or in the forum.

I try to do YouTube Videos in my room in front of a greenscreen. I know how to use the chroma key filters and everything is allright - but only if I sit still in front of my camara!

If I move a litte bit too much, or I get closer or more far away from my camera, or I put on a white shirt for example, my camera changes the exposure automatically. Unfortunately this changes the green color temperature of my greenscreen on my recording. So in my recordings my wall is light green in the beginning, but when I wear something white my wall gets dark green. Normally I wouldn’t mind, but this leads to unexpected results with my chroma key filtering, and this leads to super ugly videos.

So here comes my question: Is there a way in Shotcut to correct exposure level frame by frame? For this I’d like to select a small portion of my greenscreen, and Shortcut should change the exposure of the current frame, so that my selected picture area is always the same green.

Or has someone any idea how to handle that (in addition to buy a camera where I can fix exposure)?

Thank you for reading and any help!

David

#2

I think, that is a camera issue…, try to find the setting for auto adjustment.
(Imc, I have a Samsung A-40, I have two main settings direct on the touch screen:
with the possibility to set the light direction
and not)
And, no, I do not think, that it is to compensate with Shotcut.

HTH

#3

You need to disable your camera’s automatic exposure.

#4

That’s correct. Especially ‘white balance’!

#5

The OP is well aware that a manual camera is the real answer to this problem, but does not have one. Two workaround options using Shotcut come to mind.

The first option is to accept the varying exposure of the camera and recalibrate your chroma key filter for each new exposure shift.

The second option is to use the Color Grading filter in combination with the waveform scope to match two video clips to each other. Ideally, there would be a gray and a white piece of paper taped to an upper corner of the green screen that you could use to get a consistent white point between shots. Then, a Mask filter could effectively crop the papers out of the final shot like a garbage matte. Then the Gain portion of the Color Grading filter could get the white points the same, and the Gamma portion could get the gray papers the same. The Color Grading filter also supports keyframes if your exposure changes in the middle of a shot. But this is a very difficult and slow way of repairing a video.

In the end, everyone is correct that a camera supporting manual exposure control is the real answer to this problem. The workarounds are labor intensive.

1 Like
#6

Fun fact: an 18% gray card, the photographic standard for decades, should read 43% on a waveform monitor per BT.709.

Your scope doesn’t have a graticule line at 43%? You can check it with an eyedropper/color picker program. It should read 111 in 8-bit digital values. Did you know that, Austin?

Here is what I have and I’m quite happy with it.

#7

Thank you for your answer. Unfortunately there is no setting. I can change exposure from “0” between “-3” and “+3”, but the camera keeps adjusting on its own. That’s why I am looking for a way to compensate that in Shotcut :wink:

#8

Thank you Austin for you ideas and your energy - especially for solution 2, that shows that it’s maybe possible.

This is a good idea. And because as long as I sit still in front of the camera, everything is perfect.

I see the difficulty, because I admit I didn’t realize in detail why this can work. On the other hand it would be super easy to install those two papers, and it would be easy to add a bunch of filters to the timeline and “prepare” the video first for the croma… But for this I guess I’s need more help, because I don’t know which filters exactly I need to use. But this reads as a good solution! :wink:

At the end, I guess I have to sit still, or buy another camera. :wink:

#9

One idea…
If I understood correctly, you use a green screen. Maybe it is Ok, if you can use another color? Maybe Black?

#10

Yeah! That was set to “Automatic”, and by changing to “Daylight” or “Cloudy” my results increased a lot.

#11

It was listed in the second option. There is a filter in Shotcut that’s actually called “Color Grading”. It has vertical adjustable bars that go from black to white and independently adjust shadows, midtones, and highlights. You can simulate an exposure shift with these.

EDIT: Oops, sorry, I forgot that I referenced Mask filters as well, and there are several ways to tackle that problem. @sauron and @Hudson555x are pros at those things and could recommend the best way. I don’t use masks often enough to know which method is best.

#12

Thank you Austin for your ideas and recommendation. After fixing my white balance, my results increased already. I’d like to check if it fits for me, before I create unneccesary additional work for you guys, but I know how and who I can follow up with my topic. Thank you so much!!

#13

Earlier, when I was still working with Adobe Premiere, there was a filter specifically for this problem, which automatically corrected the color variations. You only needed to pick a reference color and the movie section was recalculated and rendered without color variations. Maybe that would be a suggestion for a new filter in SC?

#14

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