Tuesday, August 15, 2017

Seven incredible duct tape life hacks

I have assembled seven of my favorite life hacks for the guy who always has a roll of duct tape handy.

Hack #1 - Ugly mug

Let's face it. There are many of us who are just too ugly to stomach looking at ourselves in the mirror every morning. Imagine how much better you would feel if you saw Brad Pitt looking back at you? A pic of your favorite actor, a little duct tape, and you can wake up feeling sexy!


Hack #2 - Broken mirror?

Are you in the middle of seven years' bad luck? And can't scrape up the money to replace that mirror? Just duct tape your cell phone to the mirror and put it in selfie mode!


Hack #3 - Read both sides of a newspaper

A drop of oil and you can cut your newspaper reading time in half! Ok, maybe it's not duct tape, but what real man doesn't always have a can of WD40 handy?


Hack #4 - Cell phone mute

You feel a sneeze coming on. You know that your cell phone has a mute button somewhere, but don't have the time to find the manual and look it up. Grab a strip of duct tape, and viola! You got a mute button. (BTW, did you tell your wife that you are at a "convention"? You can also use this on the camera lens when you Facetime with her.)


Hack #5 - Screen dimmer

Those darn cell phones never seem to get that whole auto-brightness figgered out. Duct tape + old man sunglasses = easy reading!


Hack #6 - Can't figger out Word?

Let's face it. Microsoft Word is just too complicated! Two strips of duct tape and a piece of paper and you are word processing with the pros!


Hack #7 - Pill storage

Doncha just hate those cumbersome, ugly, hard-to-open pill boxes? A piece of duct tape and a wall is all you need to organize your pills!



Impressed? Look for my new book in quality hardware stores everywhere.



Tuesday, August 8, 2017

The brightest crayon in the shed

People are always telling me that I am not just the brightest crayon in the shed. But which crayon is?

The yellow crayon screams out "Pick Me! Pick Me!"

Well, white is the logical answer, but yellow is pretty darn close to white in terms of brightness. And a very bright yellow can also be very saturated. In this sense, yellow is kind of an anomaly in the color kingdom. All other colors, when they get saturated (color scientist use the term high chroma), get darker.

Why is yellow such a gosh darn bright color?

Munsell agrees

I am not just making up this "yellow is a bright color" thing. Munsell agrees with me, as we can see from the Munsell color pages below, where I have circled (or ellipsed in some cases) the most saturated colors on each page of constant hue.

A selection of Munsell plates with constant hue

Some preliminary stuff

I will explain why yellow is such a gosh darn bright color, but first, I need to get some fundamentals in place.

The Cohans

Those of you who are fans of my blog (I think there are currently seven of you, worldwide) will no doubt remember a stirring blog post I wrote about the cones in the eye. The image below is a recap of the exciting opening premise of that blog, suggesting that the eye has three types of color sensors, and that they are red, green, and blue.

I looked deep into her eyes,
and suddenly and inexplicably found myself hungry for H
aagen Dazs

The excitement generated at the start of the blog post was short-lived. The whole point of the post was that the colors of the cones in the eye were not quite as black-and-white as the first guess of red, green, and blue. But, if you are taking the final exam for Color Theory 101, then red, green, and blue is the correct answer. Red/green/blue is also suitable for our purposes.

Definition of eight basic colors

The RGB Cohans in the eye (not to be confused with G. M. Cohan, who was red, white, and blue) lead to a simple explanation of the eight basic colors in Color Theory 101. This is all based on a lie, but it is a useful lie. If the red cone is the only cone that sees the light, then the color we will perceive is red. Similarly, if the incoming light stimulates only the green cones, then we see green. And guess what? If it is only the blue cones, then we see blue. I bet you had already guessed that one.



How about combinations? If red and blue cones are activated (but not the green cones) then we see magenta. If the activated cones are the blue and green ones (but not the red), then we see cyan. Finally, if blue is left out and the red and green cones get all the attention, then we see yellow.

I said finally, but really I didn't mean finally, since there are two more combinations. We see black when all the cones are inactive, and white when all three are activated.

The table below summarizes the cone responses to each of the eight basic colors in the RGB color system.

Color
Red cones?
Green cones?
Blue cones?
Black
No
No
No
Red
Yes
No
No
Green
No
Yes
No
Blue
No
No
Yes
Yellow
Yes
Yes
No
Magenta
Yes
No
Yes
Cyan
No
Yes
Yes
White
Yes
Yes
Yes

Oh... I forgot to mention... these eight colors are all the strongest colors. The cells in the table above that have "No" in them mean "zero light", and the ones with "Yes" in them mean full intensity. There are a zillion combinations where the amount of light captured by the three cones is somewhere between full on and full off. These are not the strongest colors.

The importance of the lightness channel

There is a famous experiment -- very famous, everyone has heard of it -- where an ace was flashed on a screen for an instant. If that instant is really small, then the subjects had no trouble identifying the object as the ace of spades. But if they slowed it down so that the ace stayed on the screen for just a little longer, people got all kinda cornfoozled. When the researcher extended the time just a bit more, then the subjects could readily understand that they were being shown a red ace of spades. (For those who did not grow up in a casino, the ace of spades is supposed to be black, not red.)

Here is a YouTube version of the red spade experiment

This dorky (but famous) little experiment sheds a little light on how our eye/brain works, more particularly on how the color signals are encoded in the neurons that connect the eye to the brain. There is one signal (carried on a neuron) which transmits our perception of brightness. 

This is a special signal. It arrives to the brain quicker than the other signals. When the red ace is flashed quickly enough, the signals that further narrow the color down to red don't make it to the brain in time for analysis. A little longer flash, and the red signal makes it, but the signal isn't stable enough for full pattern recognition. A little longer still, and the brain has time to parse the image out and understand the weirdness.

Not only does the brightness signal show up first, but it is far more important than the other signals in terms of our understanding the scene. I am old enough to remember complaining bitterly about being the absolute last family in the whole town to get a color TV. Well, maybe not the last, but my buddy, Gary, had a color TV well before we did. His father worked for Motorola. My father gave me the lame excuse that black and white were colors, so our TV was actually a color TV. It's a wonder that I can function as an adult at all, what with the extreme deprivation and subsequent emotional trauma that I was subjected to!

People leading colorful lives, despite living in a black and white world

The funny thing about B&W television is that it actually worked. I don't recall my father ever setting me down and explaining that light gray could mean the taupe uniforms of Andy and Barney, or it could mean a Caucasian skin tone, or it could mean Ethel's blond hair. Somehow, I just subconsciously understood the color transform, and never questioned it. At least until I enviously watched Gary's TV.

So, why is saturated yellow so bright?

We now have enough background to explain the enigma of bright yellow. One sentence brings it all together: the brightness signal which is fed to the brain from the eye is a combination of the signals from the red and green cones. There are two separate signals that encode 1) the difference between green cones and red cones, and 2) the difference between blue cones and green cones.

All colors that have red and green at the same intensity have the same brightness. A quick look at the table shows that white and yellow are the only colors where red and green are at full intensity.

And that is why yellow is such a bright color.

Tuesday, August 1, 2017

How do you define a color?

I got an interesting question from a good buddy of mine, Mitchell Vaughn, Well, I kinda exaggerate when I say good buddy, cuz I just met him. And it was online, so maybe it doesn't count? But, he said he liked my blog, so I think that's the foundation for a lifelong friendship. Yes. I am that vain.

Here is the question:

I hope you don't mind me asking you a question, which I imagine is a loaded question...but here it is: Are L* a* b* coordinates a color's undeniable "definition"? In other words, is there anything else that needs to be in place to define a color...mathematically speaking? I realize there are several measuring guidelines that need to be met like light source and angle, etc. but wanted to get your thoughts on this. 

Thank you, Mitchell

I have three answers, the first one simple and theoretical, the second one complicated and theoretical, and the third one practical.

Quick answer

Color is properly defined as a sensation inside our head. So, once we have defined the relative amounts of light that the three cones in the eye will see, the color has been defined. Well, almost. The eye, brain, and the glop in between need a reference point to establish what white is. All color understanding in the brain is compared against this white reference. But since you're talking about L*a*b* values, this has already been mixed into the soup.

Sealab stew is a hearty meal all by itself!

So, the first answer is that, yes, an L*a*b* value defines a color, provided you know what white is.

Necessary qualifications

But when we are talking about L*a*b*, we are almost always talking about the color of objects -- be it the ink on a package, the paint on a wall, or the color of a plastic part. And (OK, this is gonna sound weird) objects don't have colors.

Consider the red ace of hearts. What color is the heart? Red, of course.

I took three pictures of two aces below. The camera and cards were not moved, all I did was change the lighting. Honest to god... there was no Photoshopping in the images below. No special tricks, other than playing with the lighting.

What color is the ace of hearts?

In the image at the left, taken with "normal" lighting, we see "normal" colors. The heart on the ace of hearts is red. For the middle image, I turned off all the lights in the room and illuminated the cards only with a 456 nm blue LED. The color of the red ace of hearts is now pretty much the same as the ace of clubs; it's black.

The right-most image shows what happened when I swapped in a 626 nm red LED instead of the blue LED. Now the color of the red ace of hearts is white. Or maybe it's red?  I dunno how you would explain it. True statement: The color of the red heart is nearly the same as the color of the card stock. Subjective statements: If you call the card stock white, then the heart is white. If you call the card stock red, then the heart is also red.

I will pause while you consider the implications of this. The color of the heart depends on whether your brain has decided that the card stock is white or red.

This is an extreme example, but all objects, to a greater or lesser extent, will change color as the spectral characteristics of the light changes. I might add, two colors may match under one illumination, but not under another. The ace of hearts matches the ace of clubs at the blue light club, but matches the card stock in the red light district. My wife loves to say the word for that: metamerism. She is not all that fond of saying red light district, or any of the other words for that.

To define the color of an object, we need to specify the spectral characteristics of the light that hits the sample. 

To make matters worse, the amount and spectral composition of light that reflects from an object depends to a greater or lesser extent on the angle that the light hits, and the angle from which it is viewed.

The images below are of the same blackberry, with the same camera and camera position, but with different lighting. The image on the left has a point source of light, and the image on then left shows the blackberry illuminated by diffuse lighting. The colors of corresponding parts of the two images are not the same.

Which blackberry looks the most succulent?

To define the color of an object, we need to specify the angles of illumination and of viewing. There are an infinite number of combinations, but a small collection of combinations have been standardized so that we can actually communicate about color values. The most common choices are 45/0 geometry (which is equivalent to 0/45) and diffuse geometry.

Am I done yet? No. Our perception of color depends (slightly) on whether it is a small object (projected onto just the inner circle of the retina, called the fovea) or a larger object (which extends to more of the retina). The relative concentrations of cones are different in the fovea than the rest of the retina, so our perception of color changes.

To define the color of an object, we need to specify whether the object is small (the 2 degree observer) or larger (the 10 degree observer). In case you are not confused enough yet, I discuss standard illuminants and observers in a blog post called How many D65s are there in a 2 degree observer?

In summary, the color of an object is a property of the object itsewlf, but also of the spectral composition of the incident light, the angles of incidence and viewing, and the size of the object. Based on that, once you have specified the L*a*b* value and all of these conditions (by saying, for example, 45/0 geometry, D50 illumination, 2 degree observer), you have defined the color sensation, and the color of the object has been defined.

So the second answer is that, for an L*a*b* value to have a precise meaning, you have to specify the instrument geometry, the illuminant, and the observer (2 or 10 degree).

Note that this does not mean the object won't have a different color under different conditions. Sorry for the double negative. Lemme try again. Objects in the mirror may appear closer than they are. Product is measured by weight and not volume some settling may have occurred during shipping. No warranties are express or implied. And, the color of your tie and sport coat may not match under the funky mood lighting when you get back to your apartment.

Practical answer

There is another important definition for anyone in the business of making stuff that has a specified color. Color is defined as that thing that the customer is willing to pay you for, provided you get it correct. It is whatever is defined in the contract. Without a contract detailed enough to have teeth, the correct color is whatever the customer likes.


The astute print buyer will recognize that his Wheaties package might be sitting on a shelf right next to another Wheaties package that was printed in a different press run or even at a different plant. The astute print buyer will recognize that an off-color package (just like an off-color joke) runs the risk of sitting on the shelf until expiration date, at which time it will get thrown out, much to the dismay of everyone who hates to see good Wheaties go bad.

This astute print buyer will also recognize that metamerism could be an issue if different sets of pigments are used to create the ink on the package. In that case, the astute print buyer might see fit to define the color in terms of spectral values, or in terms of color specifications under multiple illuminants.

So, all those previous answers are just academic if you live in the real world and want to get paid for your print job!

The standards folks, I might add, are pushing for a spectral definition of colors. Various tools are being put into place to allow the standardized communication of desired spectra.

Tuesday, July 25, 2017

Is 1.0 delta E a "just noticeable difference"?

My favorite scene from Fiddler on the Roof has a group of men talking politics in the town square. One of the men says that the czar is a really great guy who is bringing prosperity to the little town of Anatevka. To this, Tevya (the main character in the play) replies "Yes... You're right." I wish I could do accents in this typed blog. Imagine a rich, deep, heavily accented Russian-Jewish voice.

Another man disagrees, saying that the czar is destroying tradition in the village. Tevye again nods his head and says "Ahhh... You're right."

Yet another man looks at Tevye and says, "Tevye, how can they both be right??!?" Tevye slowly shakes his head in agreement, "You know, you are also right."


This is the third blog post in this series about the measurement of color difference. To recap, here are the two previous, contradictory explanations about the unit of measure of color difference.

   1. The size of a DE color difference is based on the Munsell Color System, which is all about uniform spacing of colors. 1.0 DE00 is one of 76 perceptually equal steps between pure black and pure white. Color differences throughout color space are scaled to this.

    2. The size of a DE color difference is all about tolerances in the industry. For print work, 2.0 DE00 is considered pretty darn good, and 6.0 DE00 is merely "pleasing".

Naturally, I will tie this up by providing a third contradictory explanation.

What is a JND?

The year 1931 was a banner year for color science. This year saw the publication of a set of tables that directly related to the color response of the human eye. Color could now be measured. Because of this work, you can measure the spectrum of a sample with a spectrophotometer, and then use the tables to convert to a real color.

The four little bumps that all color scientists know and love

I need to explain what I meant by real color. The measurement and subsequent computation would give you a set of three numbers, X, Y, and Z, which are called the tristimulus values. The numbers came with a guarantee: If two color samples measured exactly the same tristimulus values, then they would be perceived as the same color.

But, tristimulus values have two drawbacks. First, the values are non-intuitive. It was not a simple mental task to convert back and forth between tristimulus values and our common concept of color. More importantly, there was not an answer to a very basic and important question in the color industry: How close do two XYZ values need to be in order for them to be a good match?

David MacAdam sought to answer this question in his 1942 paper, entitled "Visual Sensitivities to Color Differences in Daylight". He performed a series of experiments where the test subject adjusted knobs to make one color match another color. Naturally, even if the same test subject repeatedly performs this task, the numbers won't always come out the same. He coined the phrase just noticeable difference to describe this variability.

MacAdams's gizmo for testing color discrimination
not to be confused with gizmos for discrimination against color

MacAdam created what have become known as the MacAdam ellipses, as shown in the image below. The image below is called a chromaticity diagram, and is based on the XYZ values. The ellipses  in the plot represent regions of ambiguity, magnified by a factor of ten. According to his tests, all colors within the various regions are indistinguishable.


These ellipses are ten standard deviation units across. (He chose ten in order to make the ellipses visible.) By my calculation, roughly 39% of all observations would be within ellipses of one standard deviation unit, and about 87% should be within ellipses that are twice the size.

This was a landmark paper. There have been something over 1,100 citations to it. The basic concept in MacAdam's paper was an enormously important realization for everyone who needed to put conformance ranges around color values. If you were to use XYZ as a target value for a color, then you have to allow different acceptance windows for every color and for every direction of color change. Yuck! 

Here is an interesting factoid: the MacAdam ellipses are a counterexample to Stigler's Law of Eponomy. Unlike virtually every other scientific discovery, history has correctly named these ellipses after the person who first described them. Then again, if Stigler's law is infallible, then Science has lost the name of the person who originally proposed the MacAdam ellipses.

A moment of candor with John the Math Guy

I Googled some names, and could not find anyone by the name of Avard Håkansson. Since the name of the original inventor of the MacAdam ellipses is lost, and the name Avard Håkansson is lost, it logically follows that the ellipses should be named the Håkansson ellipses. I am circulating a petition to update the 1,100 or so papers, and the 40K+ websites that refer to the MacAdam ellipses.

MacAdam's paper spurred interest in finding some transform to apply to tristimulus values that would lead to a color space that is uniform. Many attempts have been made at this. I have previously blogged on that subject (boy, that's a surprise), and in my normal obsessive compulsive way, I identified 14 different attempts between 1989 and 2010 alone.

Here's a bigger surprise. I am aware of only a handful of color spaces that were directly based on the MacAdams ellipses. Two were developed by a trio consisting of Friele, MacAdam, and Chickering, and are eponymously called FMC-1 and FMC-2.

The set of equations for FMC-2 are described in the 2002 release of the standard ASTM D2244:02. This document describes the equations in an annex with the title "Color Spaces and Color Difference Metrics No Longer Recommended But Still in Use". The 2004 version of this standard omitted this annex. It is my understanding that the last person who was using FMC-2 retired in 2003.

Here is an interesting factoid: Evidently, just like Fleetwood Mac, Simon and Garfunkel, and the Beetles, there was a falling out between these three gents, and Friele went on to develop the FCM color space by himself in 1978. The new acronym stands for Fine Color Metric. Just imagine the outrage when MacAdam and Chickering found that the acronym did not include their own names!

So, long story short, a just noticeable difference is based on the work of MacAdam on the smallest differences in color that a person is able to discern. To the best of my knowledge, there are no color spaces developed directly on this work that are currently commercially available.

Are they the same? 

I have heard it said that 1.0 DE is 1.0 JND. Is this true?

It is worth noting that CIE 142-2001, which defines DE00, does not include the name "MacAdam" as a reference, or include the phrase "just noticeable difference". So clearly the answer to that rhetorical question is no. Further, a JND and a DE are based on different data sets, so they will differ numerically.

There is a somewhat more philosophical answer, however. One of these measures of color difference is based on perceptibility, and the other on uniformity. Are these ultimately related? I propose a gedanken experiment.

Supposed that I create the gray-to-burnt-orange ramps (described in a previous blog post) in a slightly different way. Instead of basing the ramps of finer and finer subdivision of the range from gray to burnt orange, what if we arranged the spacing of the colors by taking very tiny steps from gray to burnt orange. Each tiny step would be a just noticeable difference.

The development of a JND scale (top) versus
the development of a perceptually linear scale (bottom)

Would the spacing on the two ramps be kinda the same? Another way of asking that question: When my brain makes a judgment call about midway-ness between two colors, does it count JND steps to reach that conclusion?

I don't know. I suspect that there is not a "color midway-ness determination area of the brain". I don't think it is a fundamental concept, and as such, there is a lot of variability in what people might call midway between two colors that are a modest distance apart. I have a set of special brain probes on order through Amazon. When they arrive, I will get right on that question about what's going on in my brain. My wife has been wondering about that for years.

A crinkly wrinkle

I have spent the better part of two blog posts trying to make it clear that the DE color difference and the just noticeable difference do not have the same lineage, so they must be different. Imagine how cruel you will think I am when this whole world comes crashing down. If truth be told, the two are very intimately related.


The formula for DE00 is universally regarded as being the second ugliest set of equations in the known universe. You may reckon differently, but I count a total of 26 free parameters that were available to tweak the equations, including the handful of parameters that were inherited from the formula for L*a*b*. The equations mix Fourier series, Pade formula, square roots, cube roots and seventh powers. There was a lot of knob-twiddling of the free parameters in order to get the equation just right.

Egad. John the Math Guys really don't like this: When regression goes bad. Finding the right model. Mathematical models.

What did the authors use to assess their tweaking? A bunch of large data sets that came from just noticeable difference experiments. While the lineage of DE00 is based on Munsell's perceptually linear color space, there was significant cross-breeding from the JND folks.

Final answer, what is a DE00?

DE00 is a unit of color difference, which has proven itself in practice as a way to assess conformance of manufactured color. It is loosely based on the equal gradations of color in the Munsell space. The magnitude (scaling) of DE00 is based on the size of a color step at the middle of CIELAB space, which was in turn based on 100 levels of gray. The size of a DE00 in other parts of color space was scaled so that the color difference is that same number of just noticeable difference units throughout color space.

Thursday, July 20, 2017

Inspirational memes

Who said that John the Math Guy can't be a sappy, Hallmark card kinda guy? Just in case it was you, get a load of these sickeningly sentimental memes that I created.

Inspiration





Love



Being cool




Ok, so I couldn't write a whole blog post without be silly...

Tuesday, July 18, 2017

How big is a deltaE?

Every once in a while, someone in the audience calls on me to ask a question that I know the answer to. That just happened to me, and I am soooo happy!


This is the second blog post in a series about the actual meaning of color differences. I blogged previously about the origin of the DE, in particular, the DE00. I came to the preposterous notion that "the size of a DE color difference is based on the Munsell Color System, which is all about uniform spacing of colors. 1.0 DE00 is one of 76 perceptually equal steps between pure black and pure white."

Today, I want to correct that silly idea. Contrary to what certain bloggers have said previously, the color difference DE00  is a unit of measure which is used for industrial color-difference evaluation. This color difference equation is officially defined in the document Improvement to Industrial Colour Difference Evaluation (CIE 142-2001). The summary of this document starts out with  the sentence "Recommended practice for industrial colour-difference evaluation is presented." (The italics are mine, added strictly to heighten the excitement.)

The question that sparked this series of blog posts

Here is the question that I got from my good buddy, Larry Goldberg. As you will see from his question, he is eloquent, piquant, and just a tad irreverent; three qualities I appreciate in a friend. He works for a little company called Beta Industries, where you can get microscopes and print measurement devices and a variety of other devices for the print industry.

Here is his question:

I'm looking for The Idiot's Guide to delta E, converting scientifically rigorous results to Foolproof Rule o'Thumbs.  Or the more linguistically acceptable Rules of Thumb. Or until the new, improved Fool is released.

Something in simple tabular form such as;

delta E 2000  |  Rule O'Thumb
======================
0                         Deadnuts!
1                         Just Noticeable Difference, depending on who's asking and how much they drank for lunch
2                         Winner Winner Chicken Dinner!
3                         Good commercial color match, Kwitcher belly-achin', looks good to me!
4                         It'll be perfect when you add a little more snap to the magenta.
5                         Whaddya expect on this crappy paper?
6                       TWICE as good as commercial color match, no?  No. The buyer needs another dinner and round of drinks.
7 - 10                Roses are red, violets are blue, the grass is green the sky is blue.  Run it, they'll be wrapping the fish in it tomorrow.
>10                     This is a lot better than when they printed black and white...

If you have a dissertation, or a link, or a suggestion, it would be greatly appreciated.

Boy, have I got a technical paper for you!

The Committee for Graphic Arts Technologies Standards (CGATS) has been feverishly working on a standard that ties numerical color difference to lexical color difference. The title of the standard is "Graphic technology — Printing Tolerance and Conformity Assessment". Those of us in the biz affectionately know it as TR 016. The technical report is free, by the way. Just click on the link in the sentence before the sentence before this one.


This technical report is all about making that critical decision about whether a printed product has conformed to tolerances for color. Yes, this is the stuff of which contracts are made. Come to think of it, citing this document in a contract could simplify an agreement between print buyer and printer. I wonder if the folks on the CGATS committee ever thought about that? I'll hafta mention it during the next meeting I attend.

TR 016 defines four levels of acceptance, with explanations for when these levels are appropriate. Each of the levels has an associated tolerance for color difference (in DE00), and states that 95% of the production samples must have a color difference less than the number. In other words, most of the measurements must be within this tolerance.

Here are the levels:

    Level 1 - "the most color critical applications, e.g., proofing" - 2.0 DE00
    Level 2 - "color critical applications, e.g., commercial printing" - 3.0 DE00
    Level 3 - "utility process color printing" - 4.5 DE00
    Level 4 - "pleasing color" - 6.0 DE00

So, there you have it. The size of a DE color difference is all about tolerances in the industry. For print work, 2.0 DE00 is considered pretty darn good, and 6.0 DE00 is merely "pleasing". Within printing, it is expected that the ink will be kept to a higher tolerance than the print using that ink, and the printing of a proof must also be tighter than the printing of the final product. Kinda makes sense. The variation in the color of the stuff coming out of the print shop can't be any better than the variation of what goes in.

Other industries may have tighter or looser tolerances for color. Please add to the comments below if you know about color tolerances in other industries!

Pondering

Consider this: The tolerances for color are based on a scheme for equal steps of color, which is where the DE came from. Somehow it seems a bit odd to put those two together. But one big benefit of this scheme is that it is based on our perception of color. That's a good thing, since our perception is certainly not linear with reflectance. Another big benefit is that our perception of the size of a DE00 is largely independent of the color that you are looking at. That is, we don't need different tolerances for different colors or directions of color change.

On the other hand, I would argue that our acceptance of a difference in color between two samples is not necessarily the same as our perception of the gradations of color, especially when those two samples are not side-by-side. We are much more discriminating when we see two bags of potato chips sitting next to each other on the shelf.

A color that is slightly off will sit on the shelf until expiration date

And when the colors are not side-by-side? I would argue (without much data to support this) that our brain is much more forgiving of color changes that are strictly changes in lightness or chroma than they our of changes in hue. I would also argue (again without a grain of evidence) that we tolerate differences much better if the whole image has that same sort of shift. And once again without anything to support this, I claim that the brain is much more forgiving of colors in busy images with lots of fine detail.

Comparison of a health food drink ad in a glossy magazine and on newsprint
(Images courtesy of JMG Design Services)

There is a committee in the CIE (TC8-16) that is currently working on trying to quantify Consistent Colour Appearance -- what is it that makes our brain accept the two images above as being "kinda the same", versus if those two images were shifted in hue? There are some bright and knowledgeable minds working on this committee. And then there is one dim-witted slacker who just sits around and writes self-important blog posts all day.

But on the third hand, industrial tolerances with DE00 are amenable to measurement with existing technology. What good is a unit of measure if you can't find a ruler?


That's all for part 2 of this trilogy of blog posts. Stay tuned for part 3, where I revisit the phrase just noticeable difference, and admit that the first two parts of this series were nothing but lies!