How to count freckles.

March 30, 2005 10:33 PM

I have many freckles. What's the best way to count them?
posted by swift to Science & Nature (20 answers total)

Paid servants.
posted by Jairus at 10:42 PM on March 30, 2005

sharpie and a pad of paper?

while not really sure why you would want to do so it would seem the problem would be that in counting you might 'lose your place' and the only solution I see to that is to mark each freckle as you count it. That said eventually you are going to wind up with freckles that you won't be able to see and not only are you going to need to know how to count them, you'll need to be able to convince another person to assist you in this task.

One alternative may be to take a full body scan or better yet a self panoramic photo so that you are sure you cover your entire surface area, and then apply the marker trick, however w/o the temporary staining. Still one concern would be that you would need to be certain as you create your full body model that you are clear on the overlaps and don't count a freckle twice.

Not having freckles, that I'm aware of, to say for sure, I would also assume that there may be true freckles however that may not be visible due to their location and lack of light able to be shined on them, if you understand what i'm saying.
posted by [this is good] at 10:45 PM on March 30, 2005

Draw a grid on your face with a washable ink, count the freckles in each grid, write down the total for each grid as soon as you count it. check off that grid on your face so you don't double-count, add up the grand total.

Wash face. Repeat twice. Average.
posted by mono blanco at 11:10 PM on March 30, 2005

Use body paint, in a color in sharp contrast to the color of freckles.
posted by ori at 11:33 PM on March 30, 2005

Shave your entire body. Divide your skin into regions with washable ink. Have someone take a digital photograph of each region. Manually crop the photographs to get rid of the overlapping areas (Photoshop/GIMP shape select tool should make this easy). Write some image processing code to first isolate the freckles (maybe an intensity threshold, with magnitude determined by average intensity in a small neighborhood) and then count them.

Alternatively, "one at a time." Or perhaps, "very carefully."
posted by Galvatron at 11:51 PM on March 30, 2005

Just take a scalpel, and make a pile of freckles. (Have a friend help get the freckles off your back.) Then weigh one freckle, weigh the pile, and divide.
posted by nicwolff at 12:42 AM on March 31, 2005

Hey, I was being serious! The grid technique is commonly used in archeology and other disciplines, such as ephelisology and lentiginology.
posted by mono blanco at 1:54 AM on March 31, 2005

For a rougher count, do the grid (maybe mentally), calculate your surface area, count the freckles in one little square and multiply by the ratio of that square to your whole body.

That'll be much rougher, as freckle density varies wildly. At least, I hope it does for you.
posted by NickDouglas at 5:50 AM on March 31, 2005

macro photo + photoshop + image analysis filter [used for things like counting cells in microscope slides.]

or just print out an 8x10 picture of each quadrent of your face, and then number them.

you could scan in your whole body, also. i've done that to other people.
posted by th3ph17 at 5:59 AM on March 31, 2005

This just popped into my head. I'm actually going to try it out today to see how well I can make it work.

Mark off large sections of your body with some type of vegetable ink (or other skin safe) marker.

Lightly powder yourself (to eliminate glare).

Take high resolution digital photos of each section (the ink is to show the overlap points in the photo). Harsh white light would be best (white led flashlight - I'm trying this with my ultra bike lamp). Don't use a flash. A thought: use your light source for the section marking. Mark off areas that are completely in the cone of light.

Open the photos in photoshop, gimp or some other decent photo editor. Here's where it gets fuzzy. You need to tweak the color and contrast settings to make the freckles prominent. I only have a few, and I was just able to isolate them all. It all depends on your skin coloring and tone.

Your eventual goal is to get to the point where you convert the image to black and white (not grayscale). The image should be nothing but white background and black dots.

For the counting bit, you'll need some image processing software. I have a few apps in mind, but I'd like to test them before committing to one.

And dammit. I just looked up and saw Galvatron's answer. How did I miss that??

Oh well. I'm still having fun and I'm really excited about this! I'll try to remember to report back with my results.
posted by zerokey at 6:03 AM on March 31, 2005

How exact of a count are you looking for here? As they say, this is one of those things you can do quickly, cheaply or well, but not all three.
posted by box at 6:04 AM on March 31, 2005

Response by poster: Well, not necessarily exact. An estimate would be fine if I knew how to go about estimating things like this. I'm no physicist, but I think there are easy ways to estimate things like, you know, the number of golf balls that would fit in the moon, or how many stars are in the sky. These are the kind of mental/statistical tricks I wish I knew for this problem.

I was thinking about doing something like marking off a section of skin in an area where the freckles are most dense, counting the freckles in that box, and then just measuring the total area of skin where the freckles are pretty dense to get a rough idea. But I don't know how to measure the area of something so irregular, and also the freckle density varies quite a bit. On the front of my arms, for example, the freckles are practically running into each other, while on the back of the arms there are hardly any. On the legs the and shoulders the density is different, too.

However, I hadn't even considered that image processing software could do the trick.
posted by swift at 6:22 AM on March 31, 2005

Rainman!
posted by SparkyPine at 7:37 AM on March 31, 2005

Best answer: if you have images and want to detect the freckles automatically, you could use the software astronomers rely on to detect the positions of stars. the traditional route is via iraf, and this flowchart shows the steps involved (you don't need to go past apphot unless you want to measure how big/dark each freckle is. sextractor is another solution. since the tools expect bright stars against a dark background, you would need to negate the image.

the more "modern" approach (ie still under development, infrequently used, but some people believe it's "the future") is to use web services - places on the net which process the data for you. astronomers (or the software engineers they employ) are constructing a "virtual observatory" around this approach and as part of that work, sextractor is available as a web service (iraf can also run as a web service, but i'm not sure if that functionality is available publicly anywhere yet).

disclaimer - i work with the same people that produce iraf.
posted by andrew cooke at 7:50 AM on March 31, 2005 [1 favorite]

And make sure to destroy the digital photographs when you're finished, or else you'll have naked pictures of yourself with a grid drawn on you, floating around some website.
posted by stovenator at 7:51 AM on March 31, 2005

Why do you need to count your freckles?
posted by elisabeth r at 9:09 AM on March 31, 2005

Damn. I wanted to be the first with the sharpie idea. I'm way too late.

Though, I'd have a friend with a sharpie. As the friend marks each one, he/she puts a tick on a paper and so do you (on a separate paper). Then, you tally and compare results.

Results don't match? Simple! Different colored sharpie.
posted by SlyBevel at 9:27 AM on March 31, 2005

Best answer: Try researching crowd control estimatation. All I know about it is what I've gleaned from suring the internet, undoubtedly from MeFi posts. Here are my fuzzy recollections of how one researcher handled counting people at the Million Man March.
1)Take pictures. Use a marker to create borders so that you can align images without overlap. Overlay a grid.
2)By casual inspection mark off areas with similar freckle frequency. Think of a topographical map where instead of elevation you are using freckle frequency.
3)Measure the area of each region by counting grid squares.
posted by stuart_s at 11:03 AM on March 31, 2005

With the assistance of an adoring and patient lover.
posted by Decani at 12:21 PM on March 31, 2005

Response by poster: Why do you need to count your freckles?

"Know thyself."
posted by swift at 4:59 PM on March 31, 2005