What is Pre-Flashing in Motion Film Production?
Controlled Light Exposure
Cinematographers who use strictly standard definition and HD digital video forget exactly how many alterations have to be made to film stock to get the look you like. You do not simply have the luxury of going into a simple digital menu and changing a few settings. Instead you have to select specific film stocks, communicate with the lab, and then apply certain other techniques to manipulate the film in the way that you want. Film stock is light sensitive and a controlled level of light immersion on the film stock will change the appearance of the overall image, whether or not it is a fast film stock. A method for this kind of controlled exposure is called pre-flashing.
Let the Light In
Pre-flashing exposing a limited amount of light onto the film stock to increase what is often referred to as the ‘base fog’ level. This process is used to bring down the overall level of contrast the image ends up having. You will also end up with more information in the shadowy areas. Pre-flashing ends up giving the film image a very distinctive look, almost a dreamlike soft appearance that is a nice texture. This has often been utilized in films that use images for emotion rather than realistic communication, which is why you would rarely see this kind of technique in strait forward documentary or educational purposes.
Color Film Stock
There are a couple options for the color of light you will use in the pre-flashing. A base white light is most commonly used to get the fog level up. If you are using a color film stock the white light will just add the desaturation and lower contrast. If you input a colored light onto the colored film stock then you will get a general color addition from that light. This will show up in the darker areas of the frame even more than in the light areas. This is great for adding a light color to an area, such as peach for summer in the past or a blue to a rainy urban environment. More often than not the white flashing is used on both color and black and white film stocks, but it is almost exclusively used on black and white film. If color pre-flashing is used on black and white film you may get unintended color traces that will look out of place for black and white images.
Pre-flashing is a complicated process that requires appropriate camera equipment and operators that know how to effectively work with color film stocks. The pre-flashing process can be definitely done by less experienced people, but you run risks since any more exposure than that in the controlled setting can ruin the film stock entirely. If you are going to do this you will have to go through several film stock tests to make sure that you like the way that the desaturation and ‘fog’ level produce.