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Filtration Techniques. Or How to print four different soundtracks Onto one piece of film To three different densities. Andrew Wales Technicolor London. From Negative to Print. Sound negative type - (Base Density) Print stock Soundtrack lamp age * Filters set up & condition *

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Filtration Techniques

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Filtration techniques l.jpg

Filtration Techniques


  • How to print four different soundtracks

  • Onto one piece of film

  • To three different densities

Andrew Wales

Technicolor London.

From negative to print l.jpg

From Negative to Print

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Sound negative type - (Base Density)

Print stock

Soundtrack lamp age *

Filters set up & condition *

* Trend factors - Unlikely to have sudden movement.

Factors affecting print density

Possible combinations of negative type print stock l.jpg

Possible Combinations of Negative type & Print Stock.


Agfa ST8DKodak 2383

Agfa ST9Kodak 2393

Agfa CP20

Kodak 2378Fuji 3519

Kodak 2376Fuji 3519D (Hi Con)

Kodak 2374

Total of 25 combinations

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Not Forgetting High Magenta!

  • Include High Magenta soundtracks and this doubles the number of filter packs!

  • Therefore, need to optimise so that each filter can be used with various combinations of negatives and print stocks.

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How to Optimise Printer Packs.

  • Each print stock has its own voltage setting so that the analogue track is printed to the correct density.

  • Within the aims set for the digital tracks, print a test onto each positive stock and work out an average filter pack for the print stocks tested.

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What is a Filter Pack

Collection of colour correcting filters selected so that when printed through the negative, gives a print density on aim.

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Filter Pack Examples

  • Analogue:

    Yellow filter (e.g. Wratten 12) + UV filter if required.

  • Dolby Digital:

    Red and yellow CC filters (+ neutral density if required) to give neutral print density aim.

  • Sony SDDS

    Red filter (e.g. Wratten 29 or Agfa L622) + neutral density filter to give cyan print density aim.

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Balancing Digital Print Aims

  • The print density aims of the digital soundtracks are dependent on the negative density (as for analogue tracks), we have found that with increasing negative density the print density tolerance increases.

  • Therefore the higher the negative density the more flexibility in filter pack.

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Tolerance of Dolby Digital Soundtracks to print density variation.

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High Magenta Analogue Tracks.

  • Need to control both the infra-red and cyan dye densities.

  • Done by adding cyan CC filters to the standard analogue filter (e.g. Wratten 12)

  • Requires careful balance of voltage and cyan filtration.

  • Like digital tracks, are susceptible to variations in base colour of the negative

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Filter Pack Problems

  • Problems with filter packs occur when the print density falls outside the range over which a good QC can be achieved.

  • This may be due to the following factors:

  • Filter fading

  • Lamp ageing

  • Non standard track negative

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Non Standard Track Negatives

  • A Non standard optical negative is one when the soundtrack densities fall outside the range where good QC results are possible using an optimised filter pack.

  • Could be caused by:

  • Soundtrack density being too heavy/light

  • Base density of the sound negative stock

  • Therefore need to print using a reoptimised filter pack

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Filter Packs Made Easy

  • Consistent optical negatives

  • High density negatives (digital) to ensure wide range of print densities available

  • Regular replacement of filters to reduce fading

  • Minimising the number of individual filters in each pack.

  • Convert all analogue tracks to High Magenta

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Cyan Dolby Digital Tracks

  • Instead of using CC filters to produce a neutral print density, use the red filter used for SDDS printing (& neutral density filters) to produce a cyan Dolby Digital print.

  • Allows for reduction of problems regarding negative base colour & filter fading.

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  • To maintain optimal printing densities, filters must be regularly monitored.

  • Requires consistent negatives (base & track densities)

  • By increasing digital negative densities, maximises print aim window

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