I’m old enough to remember the arrival of television in Australia for the 1956 Olympic Games. In those days Australian TV ended at about 10.30pm each evening with a rendition of the British National Anthem, a picture of Queen Elizabeth and then a fade to a complex set of lines and squares known as a ‘test pattern’. The test pattern was also used when the stations encountered all-too-frequent technical glitches to avoid the ultimate no-no, broadcasting black (or even worse, ‘snow’).

Broadly speaking, test patterns are designed to enable technicians to accurately align the optics and electronics in both film and video cameras. Test patterns are crucially important in studio settings where multiple cameras must be set up with as close to identical properties as possible and a great deal of time and effort is put into achieving correct alignment and especially colour setup in the period prior to a studio recording session or live transmission.

But not all colour charts are equal – indeed there is a huge variety of designs available and most alignment charts suffer from serious inconsistencies that ultimately make it extremely difficult to achieve high quality, reliable images. To help understand these issues we must take a leap into the highly technical and complex world of colorimetry – not a leap for the faint hearted!  

Enter DSC Labs 

DSC Labs was commissioned to design a high-end TV alignment system right back in 1965. Research at the time showed clearly that front-lit charts were extremely unreliable under different lighting conditions, so DSC opted instead to develop a back-lit system which ultimately evolved into their Ambi/Combi designs, used extensively in the film and broadcast TV worlds. However, research continued in an effort to produce a totally reliable front-lit alignment solution, with the impetus coming from the need for a compact chart for use in – of all things – space stations!

The result of this R&D is what DSC Labs call CamAlign Technology and the unit I was entrusted with is the CDM 28R ChromaDuMonde.  Depending on the physical size, these charts range in price from about US$1,100 (43x25cm) to US$3,300. At that price the CamAlign system is clearly for high-end professionals but it’s worth exploring the system to gain insights into the rarefied world of colorimetry.

What’s in the box?

The CamAlign CDM 28R has several components and it’s worth noting that, as soon as you open the box, it’s clear that this is a high quality professional product. The chart itself, measuring 54 x 33cm, is of solid aluminium with a highly resistant protective surface coating and a neoprene edge protector. Also included is a sturdy set of steel rods to support the chart and to easily enable the top of the chart to be tipped towards the camera. A black velvet ant-reflection panel is designed to be suspended below the lens. By ‘aiming’ the chart at the anti-reflect panel reflections are minimized.

The advantages of CamAlign compared to other commonly used systems are summarised in the following table, supplied in the user manual by DSC Labs.

Specifications	CamAlign Charts	Typical Industry Charts
Type	Front lit	Front lit
Dynamic Range	High – can be maintained in difficult lighting conditions with “AntiReflect”	Lower and inconsistent due to flare
Flare Level	Low - even under difficult lighting conditions	High - can result in gamma errors and crushed blacks
Physical attributes	Printing surface, inks and dyes are spectrophotometrically selected for maximum UV and IR neutrality	Unknown - most inks and dyes DSC tested had high IR reflection
Surface	Tough - easily cleaned with mild detergent	Delicate - easily scratched - must be protected
Construction	Rugged - Aircraft aluminum back-plate with protective neoprene border	Typically paper on cardboard
Ecology	Everything recycled except the pattern	Normally thrown out with the garbage
Economy	Trade in and receive up to 30% off new pattern	Old patterns have no value

The procedure is to first use the chart’s grayscale to align the camera’s gamma and tracking. DSC charts excel at this because they feature a full 11-step grayscale with virtually no deviation from spectrophotometric neutrality. By contrast, photocopy paper, often used to get a white balance, is notoriously unreliable, often having either a yellowish or bluish tint. Yellow-tinted paper will lead to a cool, bluish look, whereas bluish paper will tend to lead to a ‘warm’, reddish hue in the final video.

The first impression of the ChromaDuMonde chart is that the colours rare significantly desaturated. This is quite deliberate, the colours having been precisely calculated to represent real-life, mid-saturated vectorscope colours. Vectorscope and waveform patterns are more complex owing to the increased number of colours available on the ChromaDuMonde charts. The 28 colours on the CDM 28R chart tested here produce a hexagonal display for the primary colours, with the additional colours positioning themselves equally spaced between the primaries. This system allows very accurate calibration of even quite subtle colour shifts and the data can always be used to achieve precisely the same look on future shoots. The data is also invaluable when matching shots in post-production.

Correct colour balance is achieved by positioning the six basic colours in their respective boxes in the vectorscope. Many video cameras do not have individual controls for each hue, so the best advice is to adjust the overall gain until the crucial skin colours – red and yellow – are correctly positioned, even at the expense of the other colours.  This approach was used in my tests with a Sony Z1P HDV camera.

Why would you use the CamAlign chart?

There are many possible uses for a chart of this quality but four stand out as really important.

1. On a camera with sufficient controls, it is easily possible to obtain accurate colour reproduction by simply making adjustments until the various colours are perfectly positioned in the appropriate boxes on the vectorscope. This can be done prior to a shoot or in post-production, if a few seconds of video showing the chart under the relevant lighting conditions are included on the tape. Indeed, if you have access to a CamAlign chart, it would seem sensible to make this procedure a routine part of each setup, just as you routinely do a white balance in each location.

2. This chart allows simple, precise matching of multiple cameras. This is invaluable for any studio setting, but also for calibrating all cameras in a multi-camera shoot, such as a sporting event, car race or music performance.

3. By including a few seconds of video under actual filming conditions, and noting the vectorscope, waveform and histogram values, it is easily possible to match lighting conditions from different sets or locations during post-production or at some later date.

4. While it is possible to set a camera up for ‘perfect’ colour balance, it is also a simple matter to use the chart to act as a calibration for a deliberate variation from ‘perfect’, such as when a bluish cast is desired, or indeed any other special ‘look’ preferred by the DOP. Once the particular ‘look’ is set up, the vectorscope, histogram and waveform image can be used at any time to reproduce precisely this colour and brightness balance, either on set or in post.

The unique features developed by DSC Labs allow all of these procedures to be done with a high degree of confidence.  The charts are manufactured to extremely high specifications, with up to 288 points being measured and calibrated before the chart is passed as ready for sale. They are also supplied with an individual upgrade date and a generous trade-in discount when replacing a chart. The charts are designed for long life but this replacement program helps to ensure consistency over time.

Conclusion

The CamAlignCDM 28RChromaDuMonde calibration chart from DSC Laboratories is a truly precision instrument that enables accurate colour balancing and greyscale alignment. Once purchased, the chart should be used routinely on all shoots. Camera setup is simple and accurate and recordings of the chart make post-production colour grading both simple and reliable. The chart is ruggedly constructed and coated to make it simple to clean without damaging the underlying detail and the strand is beautifully built to a high standard. The price, of course, reflects the quality but when the critical importance of accurate colour rendition is factored into the overall video production cost, the unit will more than pay for itself. It really was a shame to have to pack this unit up and send it back to Canada!

Vendor:                               DSC Laboratories / www.dsclabs.com

                                             3565 Nashua Drive, Mississauga, Ontario, Canada

Price:                                   US$1,167 – $3,223 (depending on size)

 

Trade-in discount:            35% for annual replacement

                                             50% or more for EcoAlign subscription program

 

Auscam ratings 

Ease of use:                       9

Features:                            10

Build quality:                      10

Value for money:              9

 

We liked:                            Brilliant concept using 28 precision colours and neutral grayscales. Extremely high quality with robust design. Supplied stand of high quality.

 

We didn’t like:                   Price will limit use in low budget productions and by non-professionals. Otherwise nothing to dislike.

 

 

 

Figure legends

 

Fig 1	DSC Labs CamAlign CDM 28R ChromaDuMonde colour calibration chart
Fig 2	The chart is neatly supported by a set of support rods that sit on any light stand.
Fig 3	The stand is designed to tilt the aluminium chart slightly forwards to help reduce reflections
Fig 4	Under tungsten light with a tungsten preset in the Z1, the vectorscope shows a small deviation towards red
Fig 5	Still with tungsten light, but with a daylight preset, the pattern is seriously skewed towards the red, as seen in the matching video preview.
Fig 6	Tungsten light with a manual white balance shows fairly good positioning of the pattern. The symmetrical cross in the waveform monitor is also reasonably well displayed.
Fig 7	This time using daylight and the daylight preset the result is fairly poor with a noticeable red shift and downward displacement of the cross in the waveform monitor.

 

 

By David Smith

Dr David Smith is a physiologist-turned-film maker. David was Associate Producer of the IMAX feature Australia Land Beyond Time and was Senior Researcher on the ABC TV series Nature of Australia. He wrote and hosted David Smith's Earthwatch on ABCTV and was 'resident zoologist' on the Don Lane and Bert Newton Shows.

In 1987 David set up his company, imaginACTION pty ltd (www.imaginaction.net.au) and has sinced written, directed and/or filmed numerous documentaries and educational multimedia projects. He has also written six books, including two Penguin eco-thrillers. Over the past five years David has moved towards medical and health-related projects, including trauma surgery, schizophrenia and emergency medicine.

David is a Fellow of the Royal Society for the Arts and a professional member of the AFI and has always been keen to share his knowledge, especially with young budding film makers. David can be contacted at david@imaginaction.net.au.

 

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