Wednesday, October 23, 2013

Color Picker Pen

(An update to this blog post can be found at "Scribble Pen".)

As John the Math Guy, people are always asking me stuff. Often the questions are like "When are you gonna get off that darn computer and fix that leaky faucet?" Or "Why are you so ugly?" These, of course, aren't really question at all, but every once in a while I get a real question. Today, the question was "how does this gizmo work?"

The gizmo in question is called the Color Picker Pen, designed by Jinsu Park. Lemme tell you, it's pretty cool.

You start by holding one end of the pen up to an object and clicking the color scan button. A color sensor measures the color of that object. In the picture below, the pen has picked up the green of the leaf, and note that the color display (along the side of the pen) has changed to indicate green.

Grab a color

So far, this is a cute little gadget. But now the real fun begins. This is a pen, right? The really cool thing is that you can now use the pen to write with whatever color you just scanned. Kind of like the Photoshop eyedropper tool, only it works in the real world rather than in the cyber world within Photoshop. (You know, where all models are a size zero, and don't have pimples or cellulite?)

Draw with that color


But I was asked to explain how it works. The answer is simple. It doesn't. Don't get me wrong. It's a great concept, a cool idea, but, at least as shown in the diagrams, it seriously won't work. And, it was never advertised as a real product. Actually, you can find a lot of websites by googling "color picker pen", and many of them refer to this as a "concept", an idea that has not been turned into a real product. 

Internal organs of the Color Picker Pen

The sensor

The sensor for this pen is plausible. There is a color sensor available from MAZeT that would fit the bill. This is a true XYZ sensor, which means that it is a bit better than an RGB sensor in terms of color fidelity. (An RGB sensor will see some colors distorted.)  The sensor itself is shown above... certainly small enough for the color picker pen. Below the sensor is a prototype board. At the right side of the board, you will see a USB connector, so that gives you an idea of the size of the board. If you remove the USB related components on the board - which would not  be needed - you might be able to fit the board into the end of a fat pen.

MAZeT sensor and prototyping board

Of course, a few things might be missing. If I were designing this, I would likely try to add a white LED because I wouldn't trust ambient light, which can vary in intensity by many orders of magnitude. And especially since the user would generally want to push this thing right up against the leaf, effectively shielding the leaf from any ambient light. But this LED might make the whole thing too large, since it would be necessary to shield the sensor from the LED.

There is still one thing that is bothering me about the sensor, though. Below I show a closeup of the sensor end of the pen. Anything funny about it? Think now. What color is the end? It's a dark gray?!?!?  Why would an optical designer put sunglasses over a color sensor? It's pretty dark. Just taking a wild guess, I would say that it reduces the light to the sensor by a factor of 10. Not a good thing.

Close up of the sensor end of the Color Picker Pen

So far, it sounds like this could perhaps be built, but that it is unlikely that the pictures represent a real design.

The display

The Color Picker Pen offers a nice feedback feature: the pen will light up to tell you what color ink is measured / loaded. Is this feasible?  I borrowed a pen that belongs to my wife to show that, yes, such an animal exists. Those of you who know my wife, I would appreciate if you didn't mention that I borrowed her pen. I told her I was going to be fixing that leaky faucet.

Pen for writing love letters in the dark

This pen has a battery and a blue LED. Clicking the switch on the top will turn the light on or off. This could easily be done with a tricolor LED so that a wide range of colors can be produced along the side of the pen.

The battery in my wife's pen reminded me of something else that is needed. In my palpable excitement over this pen, I forgot all about the need for a battery! I didn't see a place for one, or a way to replace it, but let's just say that could be done. Since there is no evident way to replace a battery, it is sounding more like this is a concept design, and not a real product or prototype.

The other electronics

Of course, maybe there needs to be a microprocessor as well? Ok... I guess we can make some space for that. Maybe it would fit? I dunno.

The inks

Now we come to the fun part. The ink. Once again, I have taken a close up of the internal organs shot. Quite clearly, it shows a red, a green, and a blue ink cartridge. That's where the color scientist in me immediately says "nope, not a real product".

Close up of the ink

Why do I say that? Well.... Lemme ask you a question. What color inks are used in your home printer? Red, green, and blue? Nope. Sorry. They are cyan, magenta, and yellow. Below you see the four printing inks from my home printer. Cyan, magenta, yellow, and black. No red, no green, and no blue.

The inks for my printer

Perhaps I just have a cheap printer, you say? Well, that's true, but let's consider the other end of the spectrum. I put my latest Boston Proper sales flyer on my scanner, and collected this image. Note, especially in the white of her alluring eye, that there are no red, green, or blue dots. The dots are cyan, magenta, and yellow. The printing press that this was printed on cost a little more than my home printer - I dunno the exact figure, but I am putting it around $10 million. They don't use RGB inks. 

The choice of CMY (with the addition of black) over RGB is a fascinating story. I will get around to telling it sometime soon. For the time being, let me say this. If you mix red and green ink, you get a dark and dirty brown, almost black. If you mix red and blue ink, you get a very dark blue, almost black. If you mix green and blue, you get another really dark color. So, mixing RGB inks, you can make red, green, blue, and three lovely shades of black.

Let's change up the inks. If you mix cyan, magenta, and yellow, on the other hand, you can get a whole bunch more colors. Cyan and magenta ink mix to make a purplish blue. Cyan and yellow make green. Magenta and yellow make an orangeish red. If you mix all three inks, you get a dark brown, almost black.

So, my assessment of the Color Picker Pen is that no one ever built one. If they had, they would have realized that red, green, and blue don't make for a very wide collection of colors. They would have then called John the Math guy to help them figure it out and I would have recommended cyan, magenta, and yellow. Since I never received such a call, I have to assume that the Color Picker Pen was never built.

So, why are color cameras RGB? And why is a computer display and a TV RGB? Questions, questions! I will leave them for another blog!


  1. You mean the myth is "busted"? Gonna let Adam and Jamie take a wack at it?

  2. This comment has been removed by a blog administrator.

  3. I thought that looked too good to be true, hence my need to go hunting for this thing that didnt make sense once I saw that it was supposed to work outside of Photoshop. Thanks for sharing your impressive expertise.

  4. johnthemathguy, i ran into this recently,

    do share your thoughts

    1. did you check the website keenly?
      They have used cyan, magenta, yellow, black and white colors in their pen.
      It's shown down in the screenshot of ios app on that website.

  5. Dear FxSwmap - Thanks for pointing me to this. Wow. Someone actually doing this? I will add this to my "blogposts to write" list.

    1. Here is a post to the blog post on the Get Scribble pen:

  6. When was this invented?

  7. When was this invented? If I may quote from my blog: "So, my assessment of the Color Picker Pen is that no one ever built one." I will let you know when and if it ever does get invented!

  8. Someone really does need to make this though, it looks like it would have endless uses!