It is commonly accepted that digital RAW files are equivalent to a photographic film color negative. Here’s the rationale… A color negative is a physical record of how light is recorded onto the individual red, green, and blue emulsion layers of silver-based film, such as Agfa’s Agfacolor, Fuji’s Velvia, and Kodak’s Professional Portra.
Once the film is developed, it is placed in a photographic enlarger and projected onto light-sensitive, three-emulsion layers of photographic paper, each layer sensitive to red, green, and blue light. After the print is developed, the resulting image reveals a full range of colors and tones captured by the film.
From this description, the digital RAW image to color film analogy seems accurate. The color negative contains all the spectral and luminance information from the scene and the combination of various color filters and exposure times are able to produce a variety of differing versions of that scene. The same is true of RAW files.
At first blush, that makes sense. I bought into this analogy when it was first proclaimed twenty-five years ago. But through all these years, something about this analogy never quite added up, but I didn’t know why. Until now.
Here’s where the color negative analogy breaks down. While color prints were processed from color negatives, publications and coffee table books were always reproduced from (positive, or color reversal) transparencies or slides, such as Kodachrome and Ektachrome, Fujichrome, and Agfachrome.
Color prints were second-generation copies; each print produced on paper from a projected negative source (basically a picture of a picture). The (lithographic) quality of a color print was technically inferior in depth, sharpness and saturation to a color transparency. Images scanned by color separators directly from slides and transparencies were first-generation, and contained all the purist elements of the original photo, and therefor, the very sharpest printed images were reproduced from photographic transparencies.
Herbiology One: The digital data gathered and recorded as a RAW file more accurately parallels a film color positive (transparency) or slide than a color negative. Henceforth, RAW images should be the digital equivalent of color slides.
Herbiology Two: JPEG images are like dehydrated photographs reduced to an irreducible minimum of color and tonal information. Because these images contain significantly-reduced dynamic range and spectral data, JPEG images are more like Polaroid prints than full-bodied photographs.
Herbiology Three: Technically speaking, digital images are not photographs. That word was coined by Sir John Herschel from photo “light” and graph “instrument for recording” and describes a tangible photo record of an event. Digital images are not actually tangible until they are printed. This is why we call the digital recording an “image.”
That’s the way I sees it. If you have an argument with this position, take it to a higher court! In the mean time, sign up (above right) to get personal notices of future posts.
If you’d like to understand even more of what makes color work, how light behaves, and how easy it is to shape the light in your photographic images, go to http://gottaknowvideos.com and get Bright About Light!