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I was shooting in a gallery that used what appears to be a multi-colored projector and had difficulty shooting in that type of scene as the color was not even across the scene. The image shown below is what I mean, you see traces of green, blue, and yellow colors in the picture when it's supposed to be all white/gray as seen by the naked eye.

Why does this occur to the camera's output (DSLR or mirrorless) when shooting a scene that's lit by a projector? Is it the type of projector used? Is there a way to fix this or camera settings wise?

enter image description here

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It's the difference between how your camera and your eye/brain see the scene.

Many projectors scan each color channel in sequence very rapidly. It's too fast for our eyes to pick it up, as our brains average the sequence of each color channel. But if our camera is using a shutter time that is shorter than the refresh rate of the projector, it only sees part of the color sequence.

This is particularly true of most consumer cameras that use either a mechanical shutter that starts exposure on one side of the sensor and ends on the other or an electronic shutter that scans each line on the sensor in sequence from one side to the other (or from top to bottom). With the mechanical shutter, faster shutter times are exposed with the second curtain chasing the first curtain across the sensor. Only a narrow slit is being exposed at any one time. As the slit between the two shutter transitions the face of the sensor, the projector is flickering between each of the color channels it uses. Even with a shutter time of 1/8000 second, it still takes about 1/250-1/400 second for the slit between the two shutter curtains to transit the entire sensor. Electronic shutter is similar as each line of the sensor is read in sequence. When the last line is read then the camera starts reading at the beginning again.

The solution is to increase exposure time long enough to cover a full cycle of the projector's sequence as it goes through the color channels. In order to prevent overexposure, you may need to reduce ISO, close down the camera's aperture, or even use a neutral density filter.

  • If this was the cause, you would expect colour banding in the direction of the shutter movement. On the example image, the yellow colour cast can however only be seen in the upper right corner, which is surrounded by an L-shaped blue area. I am not sure what causes the colour cast here, but colour flickering and shutter movement is obviously not the cause. – jarnbjo Oct 22 '18 at 12:49
  • @jarnbjo The yellow cast is also in the shadows in the lower right corner as well. Having shot tens of thousands of frames under stadium lights flickering at 120Hz, I can tell you that the rolling shutter effect due to changing color as the slit between the curtains transits the sensor is not always uniform all the way across the frame. For whatever reason, the area without yellow in the center on the right could have been dark in the projector's image when yellow was being scanned. – Michael C Oct 22 '18 at 15:27
  • In which case you must have been subject to some other effect and believed that it has to do with light flickering and shutter movement. Interference between flickering lights and a moving shutter (or the readout of the sensor) will cause banding or stripes at some angle. It is simply not possible for such an effect to apply to rectangular areas of the image as here. – jarnbjo Oct 22 '18 at 15:37
  • @jarnbjo Please look at the image again. There is a yellow cast in the lower right portion of the frame as well, it's just darker in the shadows. the three major bands (blue on left, white in center, and yellow on right) are in the same orientation as the shutter curtain edges as they transit the camera being held in portrait orientation. If the projector does not project much yellow in the middle of the band on the right (because there's less yellow to be projected at that spot in the image it is projecting), then it won't show up. – Michael C Oct 22 '18 at 15:48
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    @jarnbjo Projectors and intelligent stage lights can produce infinite variations of time-multiplexed patterns that mess with any kind of fast or rolling shutter... – rackandboneman Aug 4 at 1:12
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If multiple projectors were used, the white balance may not have been consistent among all of them. They may have initially been set to match, but the color temperature can change as the lamps age. We don't normally perceive the differences because our brains compensate. The differences among light sources can also be exaggerated by increased saturation settings.

You can try decreasing saturation. Use layer masks to limit the adjustment to the affected areas.

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My guess is the projectors are not projecting the image in one hit like a film projector, but are scanning or interlacing red/green/blue much the same as TV's do, and your camera is faster than your eye.

If you slow the shutter speed to more than 1/10s it might "fix" the problem as your shutter is open for long enough to capture at least one full frame.

You can google how projectors & TV's work if you need a bit more explanation.

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