On Color:

A Talk with Dr. Tom Maier

Dr. Thomas O. Maier is Kodak's most senior and expert color scientist, with more than 25 years of experience in optimizing color for films, papers and digital media and systems. He is regularly called upon to provide leadership for key industry committees such as the SMPTE DC28 committee, where he was instrumental in writing the standards for digital cinema color, and the Academy of Motion Picture Arts and Sciences, where he is helping write new guidelines on the production of motion pictures.

On Film and Digital Color

Film is subtractive color and digital is additive color. Those are fundamentally different ways of creating color. What you see is wavelengths of light passing through the air and being received by the cells in the retina of they eye. Those light rays and those retnal cells have no idea how that image was created, so it's the creation of the image that is different, the subtractive versus the additive. And 'subtractive' means you start with white light - and subtract out red, green or blue to get cyan, magenta or yellow (and all the of other colors are combinations of these three basic colors). Additive means we star with blackness - and add red, green or blue (and all of the other colors are combinations of these three basic colors).

On the Problems with the Different Systems

In theory, we can generate all the same colors with either subtractive or additive systems. The problem is that any defined system - film or digital - can only generate so many colors. But, if we start with film, and we scan that film, we need to know what to do with the additive digital system to produce those exact same subtractive film colors. Because, the studios want any movie to look the same whether it is shown as a film movie or a digital movie. And that can be a challenge because there are some colors that one system can make and the other one can't. Those are called 'out of gamut' colors.

On Dealing with the Color Gamut Problem

So people sat down and said, "This is a very pleasing and generally acceptable result if we take those colors and make them these colors…if we 'map' them intelligently from one system to another." And from that, the idea of 'color spaces' was born. Today, there is 'film color,' and there are several 'color spaces' associated with different digital media and devices. Creatives can accept the color gamuts as they are - or they can tweak them to show colors that they want.

On Defining Color

In terms of color, there are really only a few things you can define. There's lightness - that's black to white - called dynamic range or luminance. There's hue, which is red or green or blue (or the name of any particular color). And then there's chroma, sometimes called 'colorfulness,' and that is how different this particular color in a given hue is from the neutral. So those three attributes define uniquely what a color is. And then within that, we say if the colors deviate from one another in certain ways, the overall image is normal, high or low contrast. So contrast is really a perception of how 'normal' the lights and darks in a scene appear to the eye.

On Bit Depth Color

Bit depth measures the chroma of each color. The number of levels of color that can be produced is equal to the number 2 multiplied by the number of bits we have. So a 3-bit system has 2x2x2 or 8 possible levels. Many computers use 8 bits or 2x2x2x2x2x2x2x2 or 256 levels. And, in an 8-bit system - in digital projection, for example - we're breaking everything down into 256 levels of red, 256 of green, 256 of blue. If you then multiply 256 times 256 times 256 - to identify all the combinations - you can generate 16 million different colors, but you can only discern somewhere between 2 million and 4 million. So, it seems that an 8-bit system would work for digital projection. But it does not because an 8-bit system has increments in color that are so large as to be disturbing.

On Why More Bit Depth

The problem is that you can only go in those increments, which means you have only 256 increments of red, green and blue in the neutral. And in fact, you can discern something on the order of 2000 increments in the neutral scale and so you need to go to more bit depth - to define the chroma in smaller increments. So, if you go to 12-bit, you have billions of colors - and you can only discern a fraction of those in terms of differences - but you have 4000 increments in the neutral scale - and that's only a little more than you can see. Therefore, the digital projection system is a 12-bit system. The system is very inefficient in the use of these bits, but the neutral scale demands the 12-bit system for artifact-free images - so it is the neutral scale that drives the number of bits in the system.

On DCI's Color Specifications

DCI has chosen the 'XYZ System,' which is based on an international standard that was developed in 1931. The standard defines all colors in terms of a set of three numbers - X, Y and Z. Imagine all colors on a three-dimensional graph. Because the graph is only three-dimensional, we can have a simple equation that tells us, given this set of three numbers - which are X, Y and Z values - the unique color it defines, and how to make that color out of any set of red, green and blue additive colors. So everybody in the world, knowing those values and using high-quality measuring instruments, will know how to produce that color and when they have produced that color. It is this simplicity that allows us to make television or digitally projected images that visually match the film images and the original scene colors.

On What the Human Eye Can See

We've encoded the numbers so that each number change corresponds to a little bit less than what you can see in terms of a visual change. So, a 'one-number change' you can't see, but a 'two-number change' you can see. That allows us the gradation in color so that you don't see visual artifacts - the visual steps - due to the encoding of the color.

On Future Color Innovations

What we've really defined - and I was a prime mover in this - is something so big that it not only includes every color that a human being can possibly see, the XYZ system also includes colors that can't be seen, because it's all mathematical. So we aren't limited in that at all. There's plenty of room to make a bigger gamut with a digital projector, and there are a number of ideas on how to do that. And, I think those will come along in the future. But there will always be a minimum that everybody has to meet. And we've set a maximum, which is the entire human color vision system. You can do anything up to that.

On the Color 'Headroom' in Digital Cinema

There are colors that the digital projector can produce that film can't produce - colors that are rarely if ever produced because people just aren't used to working with this medium. That's because so much of the content today is coming from film - with an aim to go back out to film with a digital projector mimicking that. I'm not sure a lot of creative people have gotten comfortable with the capabilities of digital projection. As artists get more comfortable and confident with digital, they will begin to paint from a different palette.

On the Real Measure of Color

All through artistic history, people worked with the colors that they had, from which they were able to generate images and communicate a message. The colors that artists had 500 or 700 years ago were substantially limited relative to what we have today. And yet, they painted masterpieces that are beautiful, because they knew how to work with what they had. And, I think it's the same thing today. So when you get down to it, it's not about exactly how many colors we can display. It's about how effectively a person can creatively tell a story or convey a message or feeling, which is the real reason why anyone uses color in creating motion imagery.