Wednesday, September 19, 2012

How many colors are in your rainbow?

[1] SEM images are still back in the days of black and white. If you see an SEM image with any other colors in it, it has been colorized. Someday, someone will figger out how to make electrons with different colors, and then the images will be really, really cool. I think I’ll go file for a patent on that idea.
[2] The chromaticity diagram was an early attempt at trying to turn the spectral response of the eye into something that explained our perception of color. It was replaced by other mathematical models (in particular, CIELAB), but is still the easiest way to understand the gamut of a set of light sources.
[3] Sharp introduced the Aquos Quattron display in September of 2010 which added a fourth color of pixel, yellow. For this monitor, the gamut is expanded into a quadrilateral that gives you more yellow and orange colors.
[4] Speaking of orange… I think that carrots are a richer orange than oranges are. I think we should swap the names of these too foods.
[5] Ok, I was just kidding about that one. Reddish green isn’t a color; it’s the name of the band I am going to form after I retire from all this color stuff and learn to play the sax.
[6] CIELAB was the next big step forward in coming up with a measurable number that corresponds intuitively to our perception of color. For dinner, a movie, and plane tickets, I will come to your living room and give the CIELAB lecture to you and ten of your most intimate friends.

1. we need look no further than Joseph and the amazing technicolor dreamcoat.
the answer is clearly 29 (or maybe 27, or 26 if you're an art teacher).
red and yellow and green and brown and
Scarlet and black and ochre and peach
And ruby and olive and violet and fawn
And lilac and gold and chocolate and mauve
And cream and crimson and silver and rose
And azure and lemon and russet and grey
And purple and white and pink and orange
And blue
Newton, phah...Tim Rice and Andrew Lloyd Webber have the answers (except for silver and gold.....oh yeah, and black)

2. Great musical, Steve! That totally slipped my mind. :)

3. John, what I forgot to say was thank you for a fantastic article

4. Great article John. I thought the CIELAB point was especially interesting. If there are roughly 2 million "just noticeable" steps in CIELAB would that mean that the current standard bit depth of 8-bits/channel is sufficient for even the largest color gamuts? I've heard a lot of concern about banding with 8-bits and wide gamut but it strikes me that 16+ million colors might be enough headroom except in the most extreme, not found in nature, cases.

5. Thanks, Jeff, for seeing a very practical consideration of this somewhat fanciful discussion.

Are 8 bits enough? It would seem that maybe they are, except that they might not be distributed appropriately. The eye is nonlinear. At the high end (near 255) we might not notice a change of even a few gray levels. At the dark end, our eye is more sensitive, and one gray level might be huge.

But, on the other hand, cameras are historically not linear beasts. They have a gamma associated with them, which boosts the midrange. Industrial cameras used to have an analog circuit to do this gamma. Today they generally have 10 bits or so feeding into a look up table to make this gamma. There is usually a switch to turn this off.

As a result, there is compression in camera images at the high end, and stretching at the low end. This means that the camera sees something more similar to what our eye sees, so 8 bits isn't so bad.

But on the third hand, images don't all come from cameras, and are often displayed on a monitor. The whole gamma thing came up back when we were using CRT displays, which are very nonlinear. We needed to boost the midrange to make images look correct. Rather than fix the monitor (maybe by adding a profile) camera manufacturers jumped on a solution.

Today, monitors are closer to linear, so... I dunno what this means! I'm confused. Is there a lookup/profile between the monitor I am looking at right now, and the image that is displayed via Windows?

I guess... if an image has a gamma associated with it and it is understood that the gamma has been applied, and what the gamma is, then 8 bits might be just enough.

6. You may recall prior to softproofing, drum scanner operators could only trust the screen tint Atlas books. These were printed with the printers own press, paper and inks. The step increment bewteen blocks or patches was 5%. So, from 0-100% there wer 20 steps for each color. 20C x 20M x 20Y = 8,000 colors. Adding K for another x20 (160,000) was redundant and not needed.

Steve Suffoletto SSuffoletto@BuffNews.com