Puzzler: Data exploration solution

July 3rd, 2008

Load the data and take a first look
What is this stuff?
Reshape it!
Tricky one.
There is pattern here
Lets try the other reshape
This is it

Load the data and take a first look

load puzzler.mat
plot(c,'.')

What is this stuff?

There is a lot of data, ranges from ~0 to ~255. Makes me think it is an image that has been made into a vector. How many different ways can this data be reshaped into a matrix?

dimensions = factor(numel(c))

dimensions =
   419   557

Reshape it!

What 'luck'! There is only one pair of prime factors. Makes you think this is the right path.

d = reshape(c, dimensions);
imagesc(d)
colormap(gray)

Tricky one.

We are on the right path, but not there yet. Those values were suspicious. Why were there decimal parts for an image. Let's look at the decimal parts.

e = rem(d,1);
imagesc(e)

There is pattern here

This is the right path, there is pattern here

f = e(:);
plot(f,'.');

Lets try the other reshape

There are two possible reshapes, try the other

g = reshape(f, fliplr(dimensions));
imagesc(g)

This is it

Now just clean it up a little

h = rot90(g, -1);
imagesc(h)

Get the MATLAB code

Published with MATLAB® 7.6

By Jiro Doke

Jiro is an application engineer at MathWorks. His job allows him to evangelize about MATLAB by traveling around the country to various universities and companies. He is a MATLAB addict, but he doesn't seem to mind being labeled as one.

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6 Responses to “Puzzler: Data exploration solution”

farmboy replied on July 3rd, 2008 at 09:36 UTC :

That was it? I was trying to find RGB values and could not find the blue value….

Wow, I guess I was looking to hard.

Corey

DanK replied on July 3rd, 2008 at 09:49 UTC :

I was also looking for RGB after I found the first image. The other thing I noticed was that if you looked at 1/e it tended to be distributed in the 1 to 256 range (with just a couple of exceptions, which made me think the fractional portions were supposed to be inverted. Oh well. Overthought that one.

Dan

christian replied on July 3rd, 2008 at 11:49 UTC :

ok, you win! i find the image, but never thought the show in this post. Good game and post. thanks

Harsha replied on July 3rd, 2008 at 13:38 UTC :

As farmboy and DanK even I was trying to find RGB values after the first image…..good one though. I would appreciate Doug, if he could explain how he made this vector.

Rajanikanth Jammalamadaka replied on July 3rd, 2008 at 23:58 UTC :

Even I could get only to the first image…Nice Puzzle.

Doug replied on July 7th, 2008 at 07:58 UTC :

Seems to be a lot of interest in how I generated this puzzle. It was just kind of throw away code. Here was the basic procedure:

Get the original image from logo.m, edit in pain to add the messages.

Import into MATLAB and chop to convenient prime width and heights. Save images to disk.

Read in first image, make into a column.
Read in second image, rot90, make into a column, add a sin wave so everyone knows it is not an accident. Divide by 1000 to make it a decimal. Add to the original.

Test the solution to make sure I did this all right. This is pretty much all there was.

This idea is from steganography:

http://en.wikipedia.org/wiki/Steganography

The Easter Egg in IMAGE uses this too:
http://blogs.mathworks.com/steve/2006/10/17/the-story-behind-the-matlab-default-image/

Glad you all enjoyed, I will have to make some more puzzles.

Doug

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