FILTER CARD TREATISE

 

by

 

John Tindall

 

12/15/01

 

 

 

FILTER CARDS FOR VIDEO CAMERAS

 

This document is a compilation of the research in creating a set of color pigments that mimic the effect of camera filters through the use of the white balance feature in video cameras.  These pigments could be applied to a card (or any surface).  When a video camera is white balanced on this pigmented filter card the camera is tricked into thinking that that color is white (real white would now appear to the video camera as the complementary color of the filter card).

 

The end result is the effect of the filter on the image without using filter the camera or the lights with resulting light loss, time loss, and cost.  Additionally, the filter card will enable the cameraman to maintain a “look” though various lighting conditions because a video camera white balances on the filter card using ambient light.  For instance the same “sepia look” could be maintained indoors, outdoors or under florescent lighting.

 

 

BACKGROUND

 

In 1983 I began to experiment with filter cards to trick the white balance feature of the video cameras.  It is commonly known that in a pinch a blue color balancing filter can be white balanced through to get a “warmer” look.  This practice is far from precise and is generally used as a last resort of cameramen need to color effect a scene.

 

I discovered that in the creation of filter cards there are many problems to overcome and two big questions to answer:  How do you determine the compliment of the filter?  How do you create that precise color on a card?

 

Clairmont Camera loaned me a set of Harrison Coral warming filters and I set to work trying to create a set of complimentary colored cards.  I tried to eyeball the color using Pantone colors but it was not precise.  The Pantone colors are not available in the proper hues to be precise.  Image control is of paramount importance to cameramen – approximate values are of no use in professional camerawork – film or video. 

 

My experience in color lab work told me that I needed to use a color analyzer and an optical bench to measure the filters – but how could I create the exact complements?  I talked to photo labs and had them print colors only – it was too unpredictable.  Professional graphic printers were of no help – they would not guarantee their colors.  I tried to calibrate ink jet printers but what is the value that you program into the computer?  How consistent is the printer?  How stable are the inks?  I was no closer then the Pantone papers I used in 1983.

 

THE SOLUTION: COLOR CHAMBER / ANALYZER. 

 

I modified a photographic slide duplicator with a 3200°k quartz light source and dichroic color head by removing the slide holder and building a soft box on the top of the unit.  This created a light chamber with ultra control over the color and intensity of the light. 

 

Next I modified the copy lens to accept the fiber optic probe of a color analyzer.

 

Finally, I moved the standard (bracket) that held the lens and bellows apparatus towards the rear of the unit so that the lens was looking down on the solid top of the machine instead of into the light source.  This will become the target area of the machine.

 

With this device I can put in a photographic white target under the lens, slide a photographic filter into the light path and measure its value.  I can dial in filtration until I arrive at the exact complement of the filter.  Then, I can remove the filter and use the chamber to mix and measure dye pigments to an exact complementary color of the camera filter.