Pointing out the right colours


TV-Bay Magazine
Read ezine online
In the old days of PAL and NTSC analogue television, a vectorscope was an essential tool for examining chroma at every part for the programme production and transmission chain. This was because the colour information was carried as a phase and amplitude modulation which could be sensitive to a variety of transmission or recording non-linearities and problems. These could cause colour degradation or be completely wrong. In the digital age, colour information is carried in digits which do not usually get corrupted at each regeneration or link. So why would you want to look the chroma (colour information), portrayed on the same analogue style instrument?

In analogue television systems, there is always the potential for hue and saturation problems as well as timing and 8 field-sequence issues in PAL. In an ‘all digital’ world, the colour values are carried as a stream of numbers rather than as complex analogue waveforms. Images from cameras are essentially analogue so there is always every chance for the colour to be wrong, particularly when matching cameras to look the same. There could also be differences in lenses, optics and sensors. The human factor also comes into play, like having left the tungsten setting on when the camera should be set for daylight.

Transmission problems also exist in the digital world. Most digital transmission and recording formats use component YCbCr (or YUV), having started with RGB in the camera. Whenever format or standards conversion takes place, de-matrixing and re-matrixing are going on because there are different ‘mixes’ for the colour components between HD and SD, PAL and NTSC (actually matrix coefficients but let us not get bogged down with the maths). If these processes are not performed accurately, colour purity is going to suffer. An even more important role for the modern vectorscope is in the colour grading suite. Getting the right artistic look from shot to shot and avoiding gamut error.

Hence vectorscope displays are still very much in use but decreasingly in separate analogue instruments. Rasteriser boxes have been around for about 25 years. These can digitise both waveform and vectorscope data in such a way that a normal video display can be used in combination. Nowadays, these features can be integrated into the monitor itself. These displays are in most cases only an indication of the chroma vectors with a crude graticule.

Fully featured vectorscopes with calibrated displays can provide much more detail and the ability to switch graticules and scaling as well as homing in on a region of interest in the image. These can be still found in a stand-alone box with or without and built-in screen. More often the vectorscope can be brought up on the computer monitor as a tool or plug-in to an editing or grading package. These too can have limitations. Sometimes their speed is well below real-time or the size quite small due to the limitations of running within the editing software. Often, the graticules looks crude or have a non-standard aspect ratio.

For real-time conventional 2D images, the Cel-Soft Reel-Check Solo uses PC software image processing that is fast enough even for 4K as well as 2K/HD vectorscope windows in combination with waveforms, audio or other displays. And there is no special hardware. This type of software product can replace the rasteriser or stand-alone box.

In the 3D world, the Cel-Scope3D software creates vectorscopes which may be combined so that left and right eye image chroma can be superimposed for comparison and matching at any scale in the same sort of way.

A vectorscope is very similar in concept to semaphore signalling with flags. It points at where the right colours should be. Other chroma display methods are also around but the familiar vectorscope styles are easy to understand and can provide a comforting consistency in the suite or on-set.


Robin Palmer is Managing Director of Cel-Soft and is currently involved with solutions for 3D & TV technology.

Tags: iss069 | cel-soft | cel-scope 3d | celsoft | celscope | vectorscope | N/A
Contributing Author N/A

Read this article in the tv-bay digital magazine
Article Copyright tv-bay limited. All trademarks recognised.
Reproduction of the content strictly prohibited without written consent.

Articles
Cloud integration: The only way is up
Francois Vaillant

In 2017 we saw the introduction of SMPTE 2110 and since then, the transition to IP has emerged as a priority for broadcasters looking to streamline their operations, decrease their footprint and effectively integrate with an industry in a rapid state of flux. A 2020 survey by Devoncroft found that almost 20% of broadcasters had already deployed SMPTE 2110, and over 25% were planning to do so. Then came the pandemic, precipitating the need for on-the-fly collaboration and accelerating the transition to remote, virtual and cloud production.

Tags: dejero | smpte 2110 | dazzl | streaming | Francois Vaillant
Contributing Author Francois Vaillant Click to read
The Cloud - a measured approach
Ciaran Doran

With the buzz of ‘cloud’ everywhere in our industry it would be natural to think that cloud is the only game in town. Isn’t it time to step back and consider very carefully how, or whether, you make that journey to the cloud?

Tags: cloud | rohde and schwarz | rohde | schwarz | Ciaran Doran
Contributing Author Ciaran Doran Click to read
Meeting the specification
Chris Smeeton

A good technical specification will detail precisely what is required, from the equipment to the cables connecting it. Many specifications will give  particular manufacturers and model numbers. On many occasions, this makes tendering simple and gives vendors a secure and fair way to bid.

Tags: CPR specification | argosy cable | fire safe cable | eu standard cable | chris smeeton | Chris Smeeton
Contributing Author Chris Smeeton Click to read
Avid and Rohde & Schwarz
Ciaran Doran

Rohde & Schwarz is the perfect ingest partner to build flexible workflows with Avid.

Tags: Rohde and Schwarz | avid | spycernode | editing | asset management | venice | Ciaran Doran
Contributing Author Ciaran Doran Click to read
Sennheiser MKE 400 hands on review and test
KitPlus

Sennheiser have just released two products aimed at simplifying audio on the move, the MKE400 shotgun microphone and the XS Lav Mic, in this review we’re looking at the MKE400.

Tags: sennheiser mke400 | sennheiser mke 400 | sennheiser mke 400 quality | best microphones for youtube | mic for youtube videos | sennheiser mke 400 hands on | microphone review | iphone videography | microphones | sound for video | camera microphone | microphone for iphone | microphone for youtube | video microphone | shotgun mics | smartphone microphone | vlogging mic | best microphone for video | shotgun microphone review | mke 400 | sennheiser mke 400 hands on review | sennheiser mke 400 test | KitPlus
Contributing Author KitPlus Click to read