Modifying RGB Color Matrix in-camera, imitating classic photographic emulsions

Ajai Nava
Apr 4, 2017
8 min read

Updated: Jan 8, 2022

Extracted from the technical paper : Colour Matrix Modifications in ‘Ajna Chakra’. The paper explores the digital image manipulation for the project, and describes the aesthetic motivations of 'Ajna Chakra'.

Synopsis

An alternative narrative, scripted by Fendi Sidi, the story is stemmed in social class issues in Malaysia from the Indian ethnic minority point of view. A story about a weary Indian lady who has conceded a life poverty, struggling to raise a disabled child, amidst a staggering figure- a violent and abusive husband. The leading lady's yogic practices, may offer her some solace raising a troubled family. As the cinematographer for the project, I suggested a camera with a CCD sensor instead of a CMOS, the CCD sensor structure is far more superior than the CMOS in terms of color capture, regardless of the added Bayer filter. We agreed on renting the Sony Cinelata range of cameras from Cinerent, Kuala Lumpur. The pre-visualization tests were executed on the Sony F35 Cinealta Camera as the primary camera, the camera's ability to deliver a 4:4:4 color pass was impeccable especially when the footage was timed and colored in post production. The camera also allowed leeway in capturing deeper blacks with texture, due to the camera's wider dynamic range and improved retention of detail at the ankle point of the camera's native gamma curve. The colorist, Ben Surong noted on the camera's ability to handle a wider gamut of color. Production design actively played an important role in retouching properties that required a new coating of paint, in order to fit the desired color palate that were corelated to the narrative arcs. Production designer Farid, fulfilled all the demands of the production, that were substantial in the processes of building visual blocks lift the narrative from its written form to a proper graphic form. Frequent trips to the locations were made, in particular a secluded beach in the town of Sepang, about an hours drive southwest of Kuala Lumpur. The beach would be where the dream sequence would be shot mostly, see figure 1. The recce trips were important but it was also informal, because of the laid-back atmosphere it provided an opportunity for me to gain insights on the director’s intimacy towards the story, as well as gauging how he would like play out his vision. Forging this bond was crucial to us as it weaved us together to form a type of speciation free from any formal forms of film structure. I had brought up the idea for a voyeuristic approach for the camera-work, to be non-intrusive & distancing the camera from the performers in the dream sequence. The lighting concept for the interiors were decided upon at an earlier stage, to mimic painterly brushstrokes, chiefly looking at Caravaggio's works for lighting inspiration and cluing color ideas from the Impressionist movement. As for the pace of the camera movement, complementing it with Erik Satie's Gymnopédie No. 1 was best suited for the somberness of the weary leading lady who conceded a life poverty, struggling to raise a disabled child, amidst a staggering figure- a violent and abusive husband.

it must The gist of cinematography is to serve the narrative first and let not be the camera the leading act.

Visual References

Wendy Whitson’s, Blue Heron Pond was a key reference material to create the look that suited the narrative. Her painting incorporated a muted, earthy, and often noted to have an impressionist's palette. Her approach to the subject matter could be summed up in her own words:

"The random grid I use in my underpaintings, is symbolic to me of the backdrop of nature, of how things are interrelated, organized and structured."

The pictorial motivation for the project was whirling around in the cinematic work of Florian Henckel von Donnersmarck,The Lives of Others (2006) . Hagen Bogdanski, the cinematographer shot desaturated colours with an unobtrusive camera work that worked with the style of the narrative. The narrative was prone to build slowly on the character, and the mundane looking environment complemented the Stasi ideological pillars.

Camera, Lens and Tests

The tests lasted 2 months before principal photography began, it was during the test an array of color modifications techniques were developed, and awaited for the director's approval. Most notably a set of color schemes that would act as a color arches for each of the three Acts within the narrative.

The Sony F35 Cinealta was the primary camera, while the Sony Pmw EX3k II was the B camera. The German optics Zeiss has been proven for its micro contrast capabilities in our previous tests, desiring a set of speedy prime lenses instead of the conveniences of a zoom, we decided to rent a set of Zeiss Distagon T series prime lens rehoused by P/S Teknik. The focal lengths for the primes were 21mm, 35mm,50mm and 85mm. The format of photography was 35mm full frame, AVCH.264 codec at 25p full HD resolution. We also rented a P/S Teknik 35mm adapter that was fitted to the Sony PMW EX3, so that it could operate the PL mount lenses.

The justification for the lens choice was primarily its ability in measured value in contrast & resolution. Capturing high contrast images without losing tonal gradation was important, especially in post-production image manipulation, if any correction or enhancement were required. And most importantly the Distagon series rendered a depth that is perceptually much better because of the low elements in the prime lens structure.

The Studio

Most of the tests were executed in the studios and labs of National Film Development Corporation Malaysia (FINAS) and Filem Negara (National Film Department), this privilege was largely courtesy of National Academy of Arts, Culture and Heritage (ASWARA) in vouching for our project.

Figure No.2 is a photograph of the set-up for the series of tests, it is basic arrangement done in order to gauge the sensors dynamic range and identify any color fallacies in the sensor. Such tests are also deemed useful in estimating the camera's native sensors ability in retaining as much information as possible, typically in post-production we could push and pull the footage for several stops until it surpasses the image quality threshold.

Rating the Camera

The first thing every cinematographer should do is always rate the camera's native ASA, regardless if the manufacturer markets it as an all round ISO achiever (ASA & ISO terms used interchangeably). The main reason for this is to get a valid ISO setting, a yardstick when pre-lighting, exposing a safe skin tone while maintaining texture as rendered as sharp resolution. The test require apparatuses such as the waveform monitor, 18% grey card and a single soft frontal light. In conclusion the camera was rated at ISO 800 with the earlier mentioned set of prime lenses. Do note that, there could be variables in the result if other lenses or when gamma curve settings are manipulated.

Color Modifications

The camera allowed manipulations on the visual quality, in terms of wider yield of exposure latitude. The in-camera option, tabs such as the Color Matrix settings allowed room to manipulate color, this is an added advantage especially coupled with the CCD sensor. While the Gamma options allowed room to compress highlights while allocating a large part of the recording signal for the midtones and shadow details.

I began experimenting with color matrix modifications in-camera, prior to the experiments it was substantial to acquire knowledge about color. As a precursor I began exploring technical knowledge of digital color mixing as well as, most importantly as a major source of reference material from Johannes Itten’s The Element of Color; Paul Zelanski & Mary Pat Fisher’s Design Principles & Problems: Chapter Color are invaluable in the endeavors of a contemporary image maker.

About Gamma settings, it allows better exposure latitude and control over details in shadows, midtones & highlights. Tests in the lab using the sensitometric curve as a guide, gave an overview on the best possible latitude of the camera. Specifically for highlights, the level of desired roll off in compression is definable and made it possible to lift highlights in post.

The Cinegamma 2 curve was the primary go to for the outdoor scenes, standard options were overridden in place for shoulder compression. To note, the color temperature deviated from proper color balancing in the dream sequence, the camera provided an option to adjust color temperature in 100-+Kelvin increments. Most of the scenes were shot during the Monsoon season with overcast weather, hard lighting was required to offset the overwhelming soft light. When it was not necessary to use extreme gamma curves in controlled environments the camera was shot at Cinegamma 4 curve for a much neutral curve.

Phase I

Color Modifications for Act I, Scene 3

RG +65 level rendered two different looks that the director was fond of, especially in the opening and ending sequence, it was further enhanced in post, thanks to the skillful editor cum colorist Ben.

The look for scene 3 in the film were influenced by the painting Blue Heron Pond, Nightfall by Wendy Whitson. Further manipulations rendered a green-blue phase of the matrix at a desaturated (-45) level to achieve a similar look with the painting, below is figure No.3. And Figure No. 4 is the still of the color modifications on set (with chip chart),the figure illustrates the manipulated matrix on the color chip chart.

Insight on Color Matrix Modifications

The color matrix settings are set with negative & positive variables, either to saturate or desaturate hues. Each color combination options are predetermined by manufacturers, for instance RG (Red-Green), the first letter indicates the color Red being modified meanwhile the second is its complimentary Green. The setting offer manipulation of color properties that affect saturation and tonal value. In order to build a proper framework certain equipment are required together with proper standard operating practices. Most notably the the Vectorscope, a high resolution HD field monitor, standard color chip chart, a SMPTE color bar generated in-camera, a light meter with reflective reading capacity, a color meter and light source that evenly illuminates the area.

Above left is a standard SMPTE colour bar generated in camera for standard color reference. While on the right is a vectorscope on a black background; the purpose of the vectorscope is mainly as a guide to keep hue & saturation levels in check. Primarily used to ensure colors are broadcast safe, by avoiding the bleeding limits.

Varied Outputs in Saturation

Modified RG -99 Modified RG+99

Modified RG -99 : Affects green, cyan & red somewhat. The green is less saturated & moves towards the yellow. The cyan moves toward a less saturated and somewhat warmer hue. The blue & magenta are slightly less saturated

Modified RG+99 : The red is slightly more saturated, like the green & magenta, which is slightly redder. The rest of the tones remain standard.

Tonal Values and Sensitometry Curve

The task is completed by identifying highlight-shadow detail fall-off, which are based on the gamma curve options. The sensitometric curve aids as a visual aid in pinpointing highlight, midtones and shadow detail, in simplified illustrations as slopes, knee and shoulder segment of the curve. The sensitometric curve is used in combination with a professional video test chart card, preferably a 10 scale dynamic range density chart. To note, it is a required practice in exposure tests to bracket from a range of one f stop to third of a stop. The choice of bracketing should take into account of filters used and the desired depth of field choices.

The dynamic range chart also provides as an efficient gauge in knowing the camera's amount of exposure latitude. This would enable the cinematographer to decide upon appropriate lighting ratios for the production.

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