Forensic Color Analysis

I spent several minutes trying to figure out what to call this post and I’m still not sure I got it right.  You decide!

Imagine yourself at this lovely pond location. You’ve brought your camera - loaded with panchromatic, (sensitive to all colors) black and white film. Standing by, are three primary color filters – red, green and blue. Go ahead and put the red filter in front of the lens and make an exposure.

In the composite above, the dark areas on the negative represent the amount of red light the pond photo possesses. Notice that there is a lot of silver stimulation throughout this red “record”. As you might know, equal amounts of red and green make yellow so there would naturally be solid negative detail in the trees. The darkest area of the negative tells us where the brightest values of the photo are. And until you look at all three records, you’ll not know if that bright area represents pure red or something else. Now, lets make an exposure with the primary green filter in front of the lens.

Would you agree that there appears to be a bit less green than red in the above negative? I say yes, except in the darkest area right above the mountains. This is the most obvious shared trait with the red record. We see good density distribution  throughout the negative, not particularly heavy – but evident. This tells us green light is evident, but not the dominate primary color. There are many shared density similarities between the red and green records. An expert would know now that there is a lot of yellow in this photograph.

We still have one color left, so lets make an exposure with the blue filter in front of our lens.

Now we have conclusive evidence as to which primary color has the least influence on our pond photo! See how it shares the same dark density traces the red and green records possess? If each record displays density in the exact same area, then we can conclude that this area is “white” or close to being white. It’s white right above the mountains, an area that was similarly stimulated in each of our negative. Other than strong sky and reflection density, the trace exposures throughout the rest of the blue negative build with the red and green light to render white tree trunks and highlights.

I’m also showing you contact prints from each of the color records. These positive prints are also called “separations”. Multiple expose each of these separations with their attendant color filters on to one piece of color film and you’ll  produce a “duplicate color negative”.

There is no better way to archive motion picture film than to make black and white separations from the original negative. Print on non shrinkable, estar based black and white film stock and you’ll have a three “records” of your original that will last hundreds of years. I’m not sure there is that equivalent for digital images yet.

And by the way, if you want to evaluate the primary color profile of any of your color photo’s, check out the channel feature in Photoshop. I sometimes prefer the blue channel for portrait printing, rather than a de-saturated treatment.

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