Archive for the ‘Blog’ Category

Of Pats and Palettes, and Peaks

Tuesday, November 27th, 2012
Ninth in a series of blog entries about color theory with live help from the ColorTheory (Step 9) .  First_post,  Prev_post, Next_post

This post will be a bit more dull, because we’re going to spend it introducing a new panel in the Color Theory application. Or, if you actually enjoy playuing with the application, it may make the application a little more interesting.

We’re adding the “Palette” panel, to allow us to stash and manipulate little pats of color.


The Appearance Layer of Color Perception

Friday, November 23rd, 2012
Eighth in a series of blog entries about color theory with live help from the ColorTheory (Step 8) .  First_post,  Prev_post, Next_post

In the last two posts, we discussed how the eye perceives color, first through its red, green, and blue cone response, then through its black-white, red-greeen, and yellow-blue opponent responses. But that isn’t the end of the story.

In this post, we’ll discuss three dimensions of color appearance- hue, luminance or value, and colorfulness or saturation. These dimensions were first carefully worked out by Munsell, but we will look at the latest model, the CIE Color Appearance Model 2002 (CIECAM02, or simply CAM02).

For the RGB model, the appearance variables are the well-known HSV- Hue, Saturation, and Value. But these are only rough approximations to the real variables, chosen to be easy to compute.

For better models, we go to the CIECAM02 model. It defines variables JCH: J for Lightness which corresponds to Value, C for Chroma which the amount of color (where the Saturation is the fraction of color), and H for hue (but measured differently from the HSV hue)

Red and Unique Green

Equal Lightness

Equal Chroma


The Neurological Layers of Color Perception

Tuesday, November 20th, 2012
Seventh in a series of blog entries about color theory with live help from the ColorTheory (Step 7) .  First_post,  Prev_post,  Next_post

To summarize where we ended the last time, we showed the RGB wheel which represents the first layer of color processing by the eye, using the three cone cell responses. But there are several pieces of evidence that the optical system doesn’t stop there.

The opponent theory of color is based on the observation that there is considerable evidence that our eyes don’t think in terms of three quantities of red, green, and blue. Rather it thinks of three pairs of opposing colors: black vs. white, red vs. green, and blue vs. yellow.

Four Unique Colors

In analyzing the opposite colors, researchers were able to identify four unique colors of red, green, yellow, and blue. The four colors you see are the ones identified by Hurvich and Jameson where unique green is that green with the least amount of yellow or blue in it, (not the color with the most intense green).


The Biological Layers of Color Perception

Wednesday, November 14th, 2012
Sixth in a series of blog entries about color theory with live help from the ColorTheory (Step 6) .  First_post,  Prev_post,  Next_post

Colors are fun to investigate, because there are so many ways to look at them, all different. all seemingly contradicting each other, and yet all correct. There are a wide variety of different color wheels, each of which illustrates something different. And here we start to look at them.

As discussed in a previous post , this arrangement originated with Newton and his investigation of the spectrum. But it’s not quite what the spectrum really shows.

Color Wheel according to spectrum

The spectrum color wheel distributes the colors equally across the spectrusm. Note that blue and green make up much more of the spectrum than the traditional wheel allows.

We now see the wavelengths (in nanometers) of light equally across the wheel. But we also see two additional labels for the ends of the spectrum, ‘>660′ for the Infrared, and ‘<420′ for the Ultraviolet. This represents the ends of the rainbow. The magenta colors between them are “nonspectral”- they will not appear in a rainbow or a prism, and they can’t be represented by a single frequency of light. Yet we see them.

Because our eyes can see all the wavelengths, all at once.


Reflected Heart Yin-Yang Symbol

Sunday, November 11th, 2012

Traditional Yin-Yang

I have long been fascinated by some of the more mathematical Chinese philosophical writings such as the binary complications of the I Ching and Tao duality. Specifically in this case, the Yin-Yang symbol of the cyclic dependence of dual principals- night to day to night; winter changing into summer, summer back to winter (my home in Minnesota is particularly prone to this cycle), and the basic notion of the Yin-Yang- when the dark is darkest and most triumphant, that only means that the ascension of the light has begun.

But the mathematical side of me has always been bothered, deep inside, by the symbol itself. Because it doesn’t really show what they say it shows. As we see in the next figure, while it may be 100% white at the top, it doesn’t start to change to black until almost one-quarter of the turn is complete. So even though there is a nice dot at the top center to show that there is always black even in brightest white, that promise is then broken for half of the turn to darkest black.


Connecting the Math to the Wheel

Wednesday, November 7th, 2012

Fifth in a series of blog entries about color theory with live help from the ColorTheory (Step 5) .  First_post,  Prev_post,  Next_post

We’ll show off the common HSV (Hue, Saturation, Value) system this time, but mostly we’re showing off more about ColorTheory application. HSV per se was developed in the 1970′s at the legendary PARC and NYIT research centers , but really they were just making the engineer’s RGB model friendlier with more painterly color models.


Yes, There’s Math in Color Theory

Sunday, November 4th, 2012

Fourth in a series of blog entries about color theory with live help from the ColorTheory (Step 4) .  First_post,  Prev_post,  Next_post

The RBG model is a simple one. There are three lights, R, G, and B. There are three numbers, each ranging from 0 to 255, each saying how bright that light should be. The lights could be the three phosphers in a cathode ray monitory, or three laser diodes in an LED display.

But that is also the difficulty with RGB from a scientific viewpoint. Each new set of lights represent a new set of colors. There was the NTSC standard for TV in 1953, with PAL for the Europeans. Adobe has one, as does Apple. Wikipeida lists a sample of thirteen different RGB standards. CYMK is even worse, as every new printer has its own CYMK color separation model.

From a scientific viewpoint, a more stable viewpoint is to base the color model by matching the cone receptors of the eye. And the most venerable of these is the CIE XYZ model (with the 1931 two degree observer), developed in 1931 on the basis of color observation experiments. So venerable that even though CIE itself has offered alternate definitions based on more recent research , the one that all current popular non-proprietary color models, including the RGB models and the CYMK models, and the CIE’s own CIELAB and CIECAM02 color appearance models, all remain based on the 1931 version.

Of particular note is the standard color model for HTML color, the sRGB model, defined in 2002. It is defined by starting with XYZ with a matrix transformation plus a nonlinear luminance function .

And now let’s show off some of the math.


The 90% Color Wheel

Wednesday, October 31st, 2012

Third in a series of blog entries about color theory with live help from the ColorTheory (Step 3).  First_post,  Prev_post,  Next_post

The Yurmby (RGB, CYM) wheel is not the original color wheel, nor is it the most common color wheel. The most common is the one first proposed by Newton as part of his prism studies and refined from there. It defines three primary colors of Red, Blue, and Yellow, and secondary colors of Orange, Green, and Purple. Only 8% of the color wheels in Google image are Yurmby, 90% are the Traditional wheel, with 2% “other”.

The Traditional wheel has been in use for almost 250 years. The first three-color printing process developed in 1710 was based on RYB, with a four-color RYBK soon to follow.

There is no doubt that the Yurmby wheel is mathematically accurate as to how it represents RGB and CYMK colors. Why does the traditional wheel insist on being so useful that it has stayed in use for the last three centuries?


The Simplest Way to Colors

Sunday, October 28th, 2012

Second in a series of blog entries about color theory with live help from the ColorTheory(Step 2) First_post,  Next_post

The first thing I want to illustrate what James Gurney calls the Yurmby wheel. It is a concise summary of the engineer’s answer to the question of color- what is the simplest way to make colors?

Additive colors

The modern engineer (for this discussion, anytime after color TV) was uses three lights to make color, one red light, one green light, and one blue light, to make up the RGB color system . This works because the eye in most people sees color through three types of cone cells, red-sensitive, green-sensitive, and blue-sensitive (there are exceptions, look here and here). It’s the basis of LED flat computer screens and it is the standard for defining color in HTML for the World Wide Web. It also goes by the name of the “additive color model” and is often illustrated by a figure like the one on the right.

But the engineers were preceded by the printers, who have been using three colors (plus black for a clean look) cyan, magenta, and yellow for full color printing since 1902 in the CYMK color system . It goes by the name of the “subtractive color model” and is often illustrated by a figure like the one to the left.

Subtractive Colors

Note that both figures cycle through the same six colors- red, yellow, green, cyan, blue, and magenta. So let’s show how they are just two views of the same color wheel.


Why I Care About Color

Wednesday, October 24th, 2012

First in a series of blog entries about color theory, with live help fromĀ  ColorTheory (Step 1) .  Next_post

This seris of posts started as an attempt to answer some very basic questions…

How can we choose harmonious colors? Colors that look good together, but also are distinct from each other?

I started with the goal of experimenting with programming web applications. But no matter what framework I started with, the first thing I always had to do was use HTML and CSS to format something that looks good. And that always devolved into issues about colors, or be happy with gray.

My initial design approach seemed straight-forward- choose a nice picture (which can be re-used in the blog banner) with good color harmony, and choose colors from the picture. You can see the results…

You can see the results in this blog and in the ColorTheory (Step 1) . The results were workable, but muddy. Picking colors that looked nice on their own and not just in the context of the picture was difficult. For example, my attempt to get a good yellow from the rear wheel in the figure only resulted in a creamy taupe without much distinction.