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Multi-Camera Matching and Creating a Streaming Picture Profile Using the Sony PMW-300K1

By using a vectorscope and a waveform and the process described in this article, you can limit or eliminate distracting color-matching issues between cameras and ensure your audience has an immersive experience--at least as it pertains to the quality of the video.

Camera-Matching Setup and Black Balance

Figure 5 (below) shows our camera-matching setup.

Figure 5. Our camera-matching setup. Click the image to see it at full size.

In order to properly match cameras, you will need the following:

\1. Cameras setup on tripods with all settings zeroed out. In the case of PMW300K1s, make sure that the picture profile is turned off before moving forward with matching (this will effectively zero out all settings).
2. White card and up-to-date chip chart (color chart) with stand.
3. Light source that will produce an even throw at the planned shooting color temperature.
4. Light meter.
5. Waveform/vectorscope monitor with stand.

Note that it is impossible to make an even white object using a video light from the top. Even in our use case, below the top is slightly brighter than the bottom. We are using this to demonstrate the more cost-effective option that still produces amazing results. Usually, a specially calibrated light box is used to adjust the shading correction. If you can afford one, it will give you better results.

Start by setting up the white card on its stand and lighting it as evenly as possible (Figure 6, below). Any variance in intensity on the card will prevent accurate matching, so do everything you can to get it as perfect as possible. In an ideal scenario, the card will be lit evenly to f/5.6 at ~320 ISO.

Figure 6. Make sure lighting is as even as possible.

Set up your cameras to shoot the white card from the same angle (ideally, all cameras would see the card from exactly the same position, but of course, this is not possible, so get them as close together as you can). The distance between cameras and white card should be such that zoom lenses are at half zoom when shooting the white card. Make sure the white card fills the frame entirely.

Set up the waveform monitor on its stand close to the cameras and run SDI lines to the monitor inputs (if you have more than 2 cameras, you may want to include an SDI router to avoid having to re-patch cables every time you want to look at a different camera).

Before beginning the matching process, run an auto black balance on all cameras. Much like white balance, this process tells the camera what absolute black should look like. In order to set Auto Black Balance, first close the lens all the way down. Then close the lens hood. No light should get to the sensor. On the PMW-300K1, the Auto Black Balance function is one option from the bottom in the Camera SET menu (Figure 7, below). Choose Execute. Once you’ve completed Black Balance for all cameras, you’re ready to begin matching.

Figure 7. Executing Auto Black Balance on the PMW-300K1.

Lens/White Shading

Next, re-open the lens hood and iris. The first step in matching cameras will always be lens shading (sometimes referred to as white shading). Every lens and every sensor has unique characteristics, and the combination will often produce uneven color across the image. Lens shading corrects for these inconsistencies by making adjustments to individual color channels (RGB) within the camera’s sensor.

Once lens shading has been completed for a given camera body/lens combo, the settings should rarely require further adjustment. In order to get ready for shading, display the waveform monitor.

Make sure that the monitor is set for a horizontal sweep. Select the desired camera input to display. Once the monitor is set up to accept the desired input, adjust the camera’s aperture so that the displayed waveforms fall around the 70 IRE mark (this should be around f/5.6 on the lens) and run an auto white balance on the camera. On the monitor, the result should look something like the pic on the right in Figure 8 (below).

Figure 8. The pic on the left shows default shading; the pic on the right shows shading after correct adjustments.

(Note: Because the PMW-300K1 was designed with the stock lens in mind, it should generally need little shading as the provided example suggests).

The waveforms are not perfectly straight from left to right, indicating that the sensor has a slight variation in how it is seeing the luminance levels within the image (the waveform in Figure 8 is displayed with a horizontal sweep). The goal of lens shading is to adjust the waveforms to be perfectly straight, thus displaying an accurate representation of the image. To achieve this, you must make individual adjustments to each of the 3 color channels. Most higher-end camera systems will have lens-shading adjustments available via internal menu or a Camera Control Unit. The PMW-300K1’s adjustments can be accessed only via the lens sub menu.

Lens shading adjustments come in two forms:

1. Parabola adjustment (Figure 9, below): A parabola adjustment affects the curve of the selected color channel’s waveform. In this example, the parabola adjustment would be used to bring the edges of the waveform up, and the center of the waveform down to produce a straight line.

Figure 9. Parabola adjustment.

2. Saw adjustment (Figure 10, below): A saw adjustment affects the angle of an already straight waveform. In this example, the saw adjustment would be used to bring the right side of the waveform up, and the left side of the waveform down.

Figure 10. A Saw adjustment.

Saw and parabola adjustments can be made both horizontally and vertically (horizontal adjustments made when viewing a horizontal sweep, vertical adjustments made when viewing a vertical sweep).

Start by making horizontal adjustments to the Green channel by selecting G from the PMW-300K1’s Shading CH option, and adjusting the H SAW and H PARA parameters as needed (Figure 11, below). You should be watching adjustments live on the monitor to determine how much of each you should apply. Once you’re happy with the green channel, move on to red, and finally blue. You should end up with the waveforms looking as straight as possible. From there, adjust the monitor to display a vertical sweep, and make adjustments to the V SAW and V PARA fields as needed, again in the order of green, red, blue.

Figure 11. Choosing adjustment options in the PMW-300K1’s Shading menu.

When the waveforms for all color channels are as straight as possible both vertically and horizontally, lens shading is complete.