One of the most important properties of an external monitor is its ability to analyze the technical merit of the signal.
A signal can be interpreted and analyzed in many ways, but here are a few ‘established’ methods:
Waveform Monitor – Displays voltage over time, and the ‘shape’ of the signal – commonly used to study luminance.
Vectorscope – Displays the relationship between two separate signals in X-Y form – commonly used to study chrominance.
Histogram – A graph showing the distribution of discrete data (for digital systems) over a defined range – commonly used to study luminance of each channel (RGB) separately, or the overall luminance of the signal.
Zebra/Exposure – When turned on, the zebra stripes are seen over areas that are overexposed beyond an established threshold. On professional systems, this threshold can be selected by the user.
Test/Control Signal – This is a standard signal with known characteristics that can be used to check for problems. Even if a monitor has this, I recommend getting a good signal generator with different kinds of signals for a more ‘impartial’ test.
The key difference between these technical methods and the controls one finds to manipulate the aesthetic image (brightness, contrast, etc) is that these don’t allow for variation. They show the signal as is, or at least are supposed to.
Having a professional grade monitor with these capabilities, for both analog and digital signals, is like having your very own truth serum. If you know what you’re doing, it will tell you how ‘good’ your signal really is, regardless of what the brochure or manual says.
Properties to judge monitors:
- Resolution – Must be able to take the native resolution and aspect ratio of the signal
- Pixel density – Must meet your viewing distance criteria
- Refresh rate – Should be 120 Hz if possible, or at least 60 Hz
- Luminance – Should be a minimum of 200 cd/m2 and the higher the better
- Color – All the standard color spaces selectable as presets, with LUT capability if possible
- Contrast ratio – Should be as high as possible, the really good monitors can show more than 10 stops or 1000:1
- Viewing angle – As close to 180o as possible
- Color depth – 10 bits if possible, but there’s nothing wrong with 8-bits only for viewing purposes.
- Precision – 10-bit processing minimum
- Weight, Power Consumption and Heat – As low as possible
- Ports – At least two 1.5Gbps BNC ports (for dual HD-SDI), an HDMI port (1.4) and Displayport
Not all monitors will have all of these features. If you want everything, expect to pay more than what you paid for your camera body.
In fact, you don’t need the best monitor on earth on a production set. Using technical tools will keep your image within the acceptable ball park. That’s what they are for!
When one puts so much thought and anxiety into getting as precise a monitor as possible, this question soon follows: Who will monitor the monitor?
Keeping tools in top shape is the job of a calibration tool. Good external monitors have in-built calibration tools, but if you can’t rely on the design of the monitor, why would you rely on the design of the calibration tool? For this reason, no matter what, I always recommend a third party calibration tool.
A calibration tool checks whether the image displayed by the monitor is what it claims to display. E.g., is red red?
Next we’ll take a look at suggested monitors for each size and camera, and the calibration tools to keep them in good shape.