Running A Temperature?

Q I recently worked on a project where I had to deal with monitors that were in the shot. We originally wanted to create some content to play on the monitors. The alternative of tracking footage in later seemed beyond the time frame allotted for the edit and well beyond the budget. Everything was created and then we got to the location and immediately ran into problems. First, everything was flickering or had some sort of bars running through it. We couldn’t see it looking at the display directly, but once it was on camera you could definitely see it. We later learned how to fix that, but once we got it fixed, the issue of color came up. Nothing looked right. We tried making adjustments to the monitors, but that didn’t help. We ended up having to go with the whole tracking scenario. Is there a fix for this problem?
Fran H.
Via the Internet

A Your first issue has to deal with the scanning of the monitors and the scanning of the image sensor in your camera. You said you were able to fix that, but I thought I should let readers know what you probably did to fix it. While this isn’t much of an issue with newer displays, if you’re using CRTs (remember them?), then dark bars moving through the screen is a problem.

The solution is to change the shutter speed. While many video cameras don’t really give you manual access to shutter speeds, manufacturers created an adjustment to correct for scanning issues. Sony calls its adjustment Clear Scan and Extended Clear Scan. It’s simple to use: You turn it on, point the camera at the screen you want to shoot and adjust the Clear Scan control until the bars go away.

Your second problem is a little more difficult. The issue you’re dealing with is a color temperature problem. An easy way to think of the issue is to recognize that the monitor is just another light source in your scene.

All light sources have a color temperature associated with them. Color temperature essentially is a measurement of how cool (blue) or warm (red) the light source in the scene is. The measurement is in degrees Kelvin (K). Unlike air temperature, the higher the number, the “cooler” the light source; conversely, the lower the number, the warmer the light source.

To understand what’s going on with your monitor color issue, let’s take the example of shooting on location in a house. If daylight is streaming in from the windows and there’s a table lamp in the shot, you would have a similar problem. If you white-balanced the camera for the daylight coming in from the windows, the table lamp would be too warm. If you balanced for the table lamp, the light from the windows would be too cool. Although you might want some of those effects from a creative standpoint, they might be too drastic.

So what’s the solution for this example? All of your light sources must be the same (or closer to the same) temperature. Right now there are two color temperatures, the daylight, which might be around 5500K, and the table lamp (tungsten), which is about 3200K.

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