Chief Technology Officer
Kodak Entertainment Imaging Division
QUESTION: What are the basic differences between the way analog images are recorded on film and digital images are recorded on electronic media?
EINHAUS: Film is a randomly sampled system. The way it works is similar to the way we see the world with our eyes. Silver halide crystals are randomly dispersed in three individual red-, green-, and blue-sensitive layers, coated on a transparent film base. When reflected light comes through the camera lens, the intensity and color of the light determine how much dye each crystal creates.
Digital cameras have sensors with uniform rows of individual sites called pixels. When reflected light comes through the lens each pixel collects photons and converts them into electrons that are stored and read out numerically. It is called a sampled system. The various digital cameras have different sensor designs. Most digital cameras use a red, green and blue pixel arrangement called a Bayer pattern. A Bayer pattern has an array of red, green and blue photosites. There are more green than red and blue sites, because the eye is most sensitive to variations in green. A Kodak scientist named Bryce Bayer invented that technology in the 1970’s and it is still widely used today. In motion picture applications it is also common to use three individual red, green and blue sensors, which receive light after it has been split into its component colors by a prism. There have been some attempts to layer the red, green and blue sensors the way that film does, but this turns out to be a difficult to do well.
QUESTION: Do the differences in the ways images are recorded on film and digital image capture make a difference in how we perceive those images?
EINHAUS: The answer is a definite maybe. Certainly there is a difference in the image itself that can be clearly seen at very high magnifications. Anyone can do this experiment themselves. If you look at a blown-up image that was captured with a digital camera, you can see a pattern of individual square pixels. Each square is an identical size and shape. Depending on the sensor design and the image processing you might also see noise and/or sampling artifacts. If you look at a frame of film projected on a screen, you will see a more continuous image. At high enough magnification, you will see noise related to the dye clouds themselves, but they will appear random. Of course, most of these differences are much less visible at more normal magnifications.
QUESTION: You made the statement that film records images the way the human eye sees the world. Can you tell us more about that?
EINHAUS: Both film and our eyes and brains are analog systems. Some people also refer to film as ‘organic.’ That is probably part of the reason that cinematographers tell us that film images tend to look and feel more natural.
QUESTION: Is there a simple way to describe how advances in film technology are enabling Kodak to transition from VISION2 to the new family of VISION3 films?
EINHAUS: If you measure the progress in motion picture technology over the years, you will find an almost linear improvement in silver halide crystal efficiency and the resulting signal-to-noise ratio. The signal-to-noise ratio is a measure of how well light is converted to information. Those continuous improvements have enabled us to make faster films without increasing noise, finer grain films without reducing speed, and extended dynamic range without reducing film speed or increasing noise. We have improved the dynamic range of the new family of VISION3 films by approximately three stops. That is a significant advance, which gives cinematographers more creative latitude to record details in shadow and highlight areas.
QUESTION: Can you quantify the dynamic range of the VISION3 films?
EINHAUS: This isn’t a uniform standard for measuring this, but if you measure the range of exposure with a relatively constant signal-to-noise ratio, the dynamic range is about 14 stops.
QUESTION: How does that compare to the best digital cameras today?
EINHAUS: Although digital motion cameras continue to improve, we haven’t yet seen a digital camera that comes close to matching the dynamic range of our VISION3 films. We have heard reports of digital cameras with up to 10 stops of dynamic range. And, we have measured some recently-developed cameras that were closer to 8 stops.
QUESTION: Why is dynamic range important?
EINHAUS: Cinematographers have mastered the art of using the dynamic range of film to record details in shadows and highlights the way the human eye sees them. In addition, the increased use of digital intermediate tools allows the creatives much greater ability to probe highlight and shadow information. That information cannot be probed if it is not present on the original image.
QUESTION: Some digital camera manufacturers are claiming that 4K matches the resolution of 35 mm film. What is the actual resolution of 35 mm film?
EINHAUS: I am often asked how many pixels there are on a frame of 35 mm color negative film. The answer is none because film isn’t a sampled system. Although it is an imperfect measure, one way to compare the two systems is to convert film to digital data through scanning and to determine at what scanning resolutions film continues to provide additional image information. For instance, we can clearly see differences when 35 mm film is scanned at a full 4K versus 3K or 2K resolution. Although there are diminishing returns, even more information can actually be extracted at 6K. If you scan a frame of 35 mm color negative film at 4K resolution, you are going to generate about 50 megabytes of data. In comparison, today’s 4K digital cameras, which share the 4K pixels between red, green and blue, generate about 10 megabytes of data per image. That doesn’t necessarily mean that 35 mm film systems create images that are five times better to the observer, but it does give you a sense of the differences in information content. In addition, film has the advantage that even higher fidelity can be obtained by simply using a larger film format, e.g. 65 mm. This is more difficult and expensive to do with electronic image sensors.
QUESTION: The second member of the KODAK VISION3 family of color negative films (5207/7207) is optimized for a recommended exposure index (EI) of 250 in daylight. How is film optimized for exposure at speeds in either daylight or tungsten light?
EINHAUS: The less complicated part of that question is how we optimize films for exposure at different speeds. The answer is that we use smaller silver halide crystals to manufacture slower films. That makes them less sensitive to light or slower with a finer grain structure. The difference between films that are optimized for exposure in tungsten light versus daylight is the relative sensitivity to red and blue. We change the balance to accommodate the different amounts of red and blue energy in the light sources, which helps to make the images look and feel natural.
QUESTION: How are those adjustments made with digital cameras?
EINHAUS: The cinematographer adjusts the red, green and blue channels to mimic what is done by selecting different film speeds that are balanced for exposure in tungsten or daylight. In some cameras this can also be done automatically. It is referred to as ‘auto white balancing.’ This can be problematic in some cameras because there is a limit to how much you can push the gain in the red, blue and green channels without creating image quality problems.
QUESTION: A study that was published last year reported that approximately 35 percent of the income earned by the seven major Hollywood studios comes from repurposing old TV programs and motion pictures on television to DVDs. How does film fit into this equation?
EINHAUS: Film is a proven archival medium that has stood the test of time. Television programs that were produced on 35 mm film decades ago look great on HDTV today. I am confident that today’s film programs will look great on future home theater screens, regardless of how they evolve.
QUESTION: What role has Kodak played in the digital technology arena?
EINHAUS: We are an imaging technology company. Kodak designs and sells digital still cameras, and we pioneered the use of digital technology in motion picture postproduction. We designed the CCD sensors used in some of the most widely used telecines. In 1991, Kodak scientists developed the Cineon digital film system, including a film scanner and recorder which could be used at up to 4K resolution. That system was initially used for film restoration projects beginning with Snow White and the Seven Dwarfs. It was subsequently used for compositing film and CGI elements of shots and other visual effects applications, and ultimately for complete digital intermediates.
QUESTION: Is Kodak continuing to invest in film technology?
EINHAUS: We continue to make significant investments in film technology because the improvements are valued by our customers. The best testament to that is the response to our VISION3 film. We listen to our customers and convert our technology into attributes that help them better tell their stories.