Colour clocking is a technique used in video and film production to accurately synchronize the colours between shots in a scene. It ensures continuity in the colour appearance across different shots and angles, creating a seamless visual flow in the final edited sequence.
Why is Colour Clocking Important?
A single scene in a film or video is rarely shot in one continuous take. It usually comprises multiple shots taken from different angles and distances. Even if the shots are of the same subject under the same lighting conditions, the colour representation can vary slightly from one shot to another due to differences in the camera sensors and lenses. This can make the editing jarring, with noticeable colour shifts as the shots cut from one to another. Colour clocking aims to correct this.
By analysing the colour information in each shot and standardising it, colour clocking ensures all shots match in their colour rendition. This makes transitions between shots seamless, maintaining visual harmony in the scene. The audience perceives the sequence of shots as occurring in the same space and time, rather than noticing the artifice of editing.
How Does Colour Clocking Work?
Colour clocking relies on measuring the precise chromatic values in each shot and manipulating them until specific parameters match between shots meant to be contiguous. Here are the key steps involved:
- The colourist or editor analyses each shot separately to detect the average chromaticity, luminance, gamma and other colour parameters.
- One shot is selected as the reference shot that determines the target colour values.
- Using colour correction tools, the parameters of the other shots are adjusted until they match those of the reference.
- Sometimes, instead of a single shot, an average reference is derived from multiple shots.
- The adjustments are refined frame-by-frame because lighting and colour can change even within a shot.
- For difficult scenes, colour charts are kept in the frame to aid measurement of parameters.
Advanced software allows tracking of skin tones, sky tones and memory colours during colour clocking. This retains the most perceptually important hues while standardising the overall values.
Colour Clocking Methods
There are two main approaches used in colour clocking:
3D LUT Based Clocking
This technique relies on using multi-dimensional lookup tables (LUTs). The colour analysis provides measurements to generate shot specific LUTs. Applying these LUTs to each shot equalises them to the chosen reference. The advantage is that LUTs provide consistent results shot to shot. However, LUTs are also inflexible in dealing with footage that changes colours internally. They are best for shots with static lighting and colour.
Software Grading Based Clocking
Here, software grading tools are used to manually adjust curves, hue, saturation, luminance and other parameters. This gives greater control shot to shot to the colourist. Dynamic or difficult footage can be clocked more effectively. But it depends on the skill and judgement of the colourist. There can be shot to shot inconsistencies if not done carefully.
When is Colour Clocking Used?
Colour clocking is common in major motion picture post-production workflows. The seamless colour it provides is vital for Hollywood calibre work. It is also gaining use in commercials, music videos and corporate videos to maintain professional, consistent grading. Types of productions where colour clocking is routinely applied:
- Feature films
- Television shows
- Documentaries with re-enactments or graphics
- Commercials
- Music videos
- Live events
It helps productions that use multi-camera setups, shoot on multiple locations, use special effects, or integrate footage from different sources. It brings all these disparate visual elements together convincingly.
Challenges in Colour Clocking
While colour clocking is a powerful technique, it also comes with its own unique challenges:
| Challenge | Description |
|---|---|
| Matching dynamic lighting | When lighting conditions visibly change within a shot, it can be hard to colour correct the entire shot to match other shots. |
| Footage from different cameras | Footage from different camera makes and models responds differently to colour correction. |
| Matching low quality footage | Low resolution or heavily compressed shots may not have enough colour information for accurate clocking. |
| Artistic liberty | Sometimes cinematographers intentionally want a difference in colour mood from shot to shot for effect. |
Skillful colourists know how to get the best possible match between shots while working around these limitations. They balance technical requirements with artistic sensibilities during the process.
Colour Clocking vs Colour Grading
Colour clocking is part of the broader process of colour grading or colour correction. It specifically focuses on technical and aesthetic continuity between different shots. Colour grading is the overall adjustments made to meet creative aims for the look and feel of the video. The goals of colour clocking are more objective and narrow compared to subjective stylistic goals of colour grading.
However, the workflow overlaps a lot. The same tools like curve adjustments, LUTs, tracking, etc. are used in both. Colour clocking also benefits from the trained eye of experienced colourists. And a well clocked sequence of shots provides an excellent foundation for further creative grading.
Conclusion
Colour clocking is vital for professional level film and video production. Matching colours accurately between shots is critical for convincing edits that don’t distract the audience. Both technical and artistic considerations come into play when clocking multiple shots to look seamless. The techniques continue to improve with advances in digital colour correction tools. While challenging, good colour clocking is one of the marks of expert visual craftsmanship.