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Color Problem

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Mike Johnston
Color Problem
on Aug 22, 2014 at 2:23:37 am

We have 3 NX5Us and love the images we get from these cameras. However, we recently started shooting in a venue that uses light washes on a white wall for a background with a combination of RGB LED and incandescent flood fixtures. The problem is that the cameras do not seem to be "seeing" the reds in the wash thus not providing an accurate image of the colors on the wall. All other colors in the image (including red items) are true. What could be causing this and is there some setting on the camera that might correct for it?

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john lenihan
Re: Color Problem
on Aug 22, 2014 at 3:50:08 pm

I have experienced the same problem and believe there is two things you can do based on what I believe are the two contributing factors.

Factor 1.
The camera subsamples the color. It records with a color sample of 4:2:0 which means is really saying that it only looks at the light intensity for every pixel and the color for every 4th pixel. The eye doesn't notice it when there are many colors, but for pure colors such as those caused by LEDs and lasers, it makes a huge difference.

To minimize this effect you could connect an hdsdi cable to the camera and add an external recorder. In this situation, the camera will produce 4:2:2 which means twice as many color samples.

Factor 2.
LEDs have narrow frequency range. If this is more detail than you want, ignore it. But the world of natural light and incandescent light produce many different colors of varying intensities. Remember that light is electromagnetic radiation the same as radio waves.

If you graph the intensity vs. frequency of sunlight or incandescent light, it will look like a bell shaped curve. The middle of the bell shaped curve is what our eye perceives as the color.

The three sensors on the camera are designed to pick one single frequency out of this bell shaped curve. One we call Red, One we call Yellow, and one we call Green. Then it only records those three numbers.

When the three colors are combined, we perceive the combined color the same as the bell shaped curve. But it is really not, it is only three colors.

In comes LEDS LEDs put out a single frequency or color. If you have a red and yellow and green LED, your eye perceives it as white. But it is only three distinct colors.

The problem arises because the exact color red that the LED is putting out many be a slightly different color red than the camera sensor is looking for. In this case, it will not record that LED color red at all. Black, not there.

The options which are not reasonable, but would work:
1. Tell everyone to stop using LEDs and Lasers for lighting
2. Use an analog camera instead of digital.
3. Never shoot in that venue.

The only way to minimize this effect is the following:
1. Be aware of this effect. And know that even though your eye in the venue sees the red, the camera doesn't see single colors very well. This goes for Blue also. For important things, bring your own light or get the subject into a multicolored light, like white.

2. Don't use the automatic white balance. The camera tries to compensate based on the faulty recognition of colors, and ends up creating weird effects. I set mine to incandescent and just leave it there.


John Lenihan

LeniCam Video Productions

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