This puzzle is part of the Monthly Topic Challenge #2: IQ Puzzle Parody

What's missing?

Puzzle Image

Hint 1 (for use after the first step):

There are three “types” of pixels. You should work through these three sets more or less linearly in some order.

Hint 2 (for use after the second step):

There are 24 slitherlinks.

Hint 3 (for use after the third step):


Hint 4 (specification of hint 3):

What is used by all three?

  • 6
    $\begingroup$ Do I get any points for "the four choices to pick between are missing"? $\endgroup$ Aug 5, 2022 at 1:37
  • $\begingroup$ What's missing? One white square per grid, why? $\endgroup$
    – Exal
    Aug 5, 2022 at 7:03
  • $\begingroup$ I'm willing to give a slight push in the right direction, but I'm not sure if I should at this point, or generally what progress people have, and I don't want to repeat something people already know... $\endgroup$
    – SeptaCube
    Aug 5, 2022 at 16:11
  • $\begingroup$ @SeptaCube any idea? $\endgroup$ Oct 12, 2023 at 18:29

4 Answers 4


Second Step

Following the clue from Auribouros's answer, if you take…

…every other pixel—that is, the pixels highlighted in red below:
The puzzle image

…and then…

…brighten the image, or equivalently color white all pixels that are not pure black…

…you will get:

A 3x3 grid of letters that spell SLTHRLNK

Third Step

Combining the clues from the first two steps, take…

…the “white” pixels…

…and look at their…

…pixel values.

For example,

…the first grid has red values:

251 254 251 251 251
254 251   2 255 251
251 254 251 251 251
253 253 251 251 251
251 253 255 251 251

Now subtract…

…the larger values from 255. In the above example this yields:

4 1 4 4 4
1 4 2 0 4
4 1 4 4 4
2 2 4 4 4
4 2 0 4 4

Finally, remove the…

…cells equal to 4, e.g.:

. 1 . . .
1 . 2 0 .
. 1 . . .
2 2 . . .
. 2 0 . .

Which yields a…

Slitherlink puzzle with a unique solution:
The solution to the slitherlink (Image from https://www.dougandjean.com/slither/, which I used to solve all of the Slitherlinks in this puzzle.)

We do this once for each grid…

…and each color channel,

…filling in the…

…pixels corresponding to the edges used in the solution with colors corresponding to the color channel,

…which yields:

A 3x3 grid of 11x11 checkerboards of pixel images filled with random-looking colors
(Click on the above image to see its individual color channels.)

Fourth Step

Thanks to doome for pointing out in their answer that if we take the…

…white pixels in the above image, their disjoint union fills the while checkerboard grid (except for one errant pixel.

So if we take the…

…pixels of the original image that we haven't used yet—which are the same checkerboard pattern—and multiply them by 255…

…we get:

A different 3x3 grid of randomly colored 11x11 checkerboards
(click on the image to see its color channels)

Then, if we take only the pixels that are…

…white in the slitherlink solutions, and combine them into one grid…

…we get:

enter image description here
(click on the image to see its color channels)

Which certainly looks like… something?

  • $\begingroup$ Great find, good luck on the rest of the puzzle! $\endgroup$
    – SeptaCube
    Aug 6, 2022 at 3:06
  • $\begingroup$ @SeptaCube Sadly I don't know enough about [spoiler] to decipher the rest. $\endgroup$ Aug 6, 2022 at 3:15
  • $\begingroup$ Nice job! Any idea what that last symbol is? A colon? An equals sign? $\endgroup$
    – JLee
    Aug 6, 2022 at 10:18
  • 1
    $\begingroup$ @JLee Just random bits of the question mark I think. $\endgroup$ Aug 6, 2022 at 14:39
  • $\begingroup$ Amazing job on step 3! I will say that rot13 (lbh'er tbvat gb jnag gb ybbx zber ng gur ybbc qenja guna gur pbagnvarq ertvba.) $\endgroup$
    – SeptaCube
    Aug 8, 2022 at 0:47

Potentially partial answer, but I think you're missing

this symbol
Square with a smaller white square removed

How do:

The removed squares correspond to numbers between 1 and 25, taking every number and converting it using A1Z26, we get the text HEXCOLOR, which might be missing an S at the end (square in the spoiler above)

  • 2
    $\begingroup$ Great start! That isn't the answer though, just a cluephrase :) $\endgroup$
    – SeptaCube
    Aug 4, 2022 at 14:29
  • $\begingroup$ Back to the drawing board it is then! $\endgroup$
    – Auribouros
    Aug 4, 2022 at 14:32
  • 6
    $\begingroup$ rot13(v qb abg unir gur raretl gb qrpvcure guvf ceboyrz va vgf ragvergl, ohg gur vzntr vf pbzcbfrq bs znal funqrf bs oynpx naq juvgr, jubfr urk pbqrf qvssre bayl znetvanyyl sebz rnpu bgure. tvira gur uvag vg vf yvxryl gung gur fbyhgvba yvrf va gung qverpgvba, ohg gurer ner fb znal qvssrerag urk pbqrf v nz abg tbvat gb grqvbhfyl cber guebhtu rnpu, yby.) $\endgroup$ Aug 5, 2022 at 0:54

Fourth Step

Following from 2012rcampion's answer, if you take…

…the resulting Slitherlink solutions for each grid, and isolate only those edges which are present in all three colors:
The common edges for all 3 colors in each grid.

…we then see…

…that all the pixels are used once each, with the exception of just one. To see this, we overlay all of them below (using the 9th grid to demonstrate this):
The common edges from before overlaid on top of each other.

Now, we look at the original image…

…and in particular, at the pixels we haven't used yet. We used the pixels in the "corners" of the grid to see the "SLTHRLNK" message, we used the "white" pixels to find the Slitherlink puzzles, but we haven't yet used the pixels lying on the "edges" of the Slitherlink.

On closer inspection…

…we find that these pixels are not all pure black. In fact, they have value 0 or 1 in each coordinate. We can increase the contrast of these pixels, as seen below:
A 3x3 grid of 11x11 checkerboards of pixel images filled with random-looking colors
(Click on the above image to see its individual color channels.)

Combining with the previous result…

…we can look at the RGB values of the missing location within each grid, getting the following values for each grid (reading the grids in the standard row-major order):
Grid: 1 2 3 4 5 6 7 8
R: 0 1 0 1 1 0 1 0
G: 0 0 1 1 1 0 0 1
B: 0 0 0 1 1 0 0 0

This is as far as I got.

I considered interpreting this several ways. Attempting to convert each color's string to ASCII gives Z9(cancel), which seems useless and incorrect. Alternatively, interpreting this as a color gives the color #5a3918, which is apparently called Irish Coffee, but I do not know how to use this either.

  • $\begingroup$ Hmm, rot13(gurer fubhyqa’g or n zvffvat cvkry, gurl fubhyq nyy or nppbhagrq sbe. Ybbxf yvxr vg’f na vffhr jvgu gur guveq tevq, abg fher vs vg’f n ceboyrz jvgu gur chmmyr be fbzr genafpevcgvba reebe…) $\endgroup$
    – SeptaCube
    Aug 18, 2022 at 17:14

Following @Auribouros's partial answer, I took a look at each of the white squares.

I found cough 'several' cough pixel colors (I color coded them to make it easier to put in my revised image):

By the way, I got pretty desperate for colors at the end there. See Wikipedia's List of Colors in case you're confused about 'what the **** is cerise?'

Red: RGB(249, 246, 247), Hex f9f6f7
Green: RGB(255, 254, 251), Hex fffefb
Blue: RGB(251, 251, 251), Hex fbfbfb
Yellow: RGB(251, 254, 254), Hex fbfefe
Magenta: RGB(251, 253, 251), Hex fbfdfb
Cyan: RGB(251, 251, 253), Hex fbfbfd
Light-Gray: RGB(251, 255, 255), Hex fbffff
Dark-Gray: RGB(254, 251, 254), Hex fefbfe
Orange: RGB(251, 255, 251), Hex fbfffb
Brown: RGB(251, 253, 253), Hex fbfdfd
Light-Red: RGB(251, 251, 254), Hex fbfbfe
Light-Green: RGB(255, 251, 251), Hex fffbfb
Light-Blue: RGB(254, 252, 251), Hex fefcfb
Light-Yellow: RGB(251, 251, 252), Hex fbfbfc
Light-Magenta: RGB(251, 252, 252), Hex fbfcfc
Light-Cyan: RGB(252, 252, 251), Hex fcfcfb
Purple: RGB(251, 254, 251), Hex fbfefb
Beige: RGB(254, 251, 251), Hex fefbfb
Chartreuse: RGB(255, 251, 254), Hex fffbfe
Electric-blue: RGB(251, 251, 255), Hex fbfbff
Mauve: RGB(254, 251, 253), Hex fefbfd
Dark-red: RGB(251, 252, 253), Hex fbfcfd
Dark-green: RGB(251, 253, 254), Hex fbfdfe
Dark-blue: RGB(255, 252, 251), Hex fffcfb
Dark-yellow: RGB(254, 254, 254), Hex fefefe
Dark-magenta: RGB(253, 251, 251), Hex fdfbfb (separate from purple; slightly lighter)
Dark-cyan: RGB(255, 253, 251), Hex fffdfb
Pear: RGB(254, 251, 255), Hex fefbff
Orange-red: RGB(253, 253, 254), Hex fdfdfe
Silver: RGB(253, 251, 253), Hex fdfbfd
Desert sand: RGB(251, 252, 251), Hex fbfcfb
Cerise: RGB(253, 253, 251), Hex fdfdfb

So far I haven't finished coloring everything, but I have got this, which I plan to expand in the future:

Pixels, revised


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