Teeny Tiny Pictures, II

[da]

This is a continuation of my previous post about photo mosaics, a project of Fish and I.

What do you get when you cross Flickr, GD Graphics Library, and a bunch of perl code?

In our case, something like this:



That is made from a corpus of 10,000 thumbnail photos from Flickr's "colorfields," "urbanabstracts," and "flowers" pools. Each tile is partitioned into a 5 by 5 grid and each of those is indexed by colours (RGB currently, HSV to come). The resulting data is stored as a 75-dimension vector.

We reduce the source image to a smaller size, such as 250x200, and each 5 by 5 grid is turned into another 75-dim. vector, which is compared with each of the tile vectors in the corpus. The closest vector is added to the image, subject to a few constraints such as not repeating nearby. A 5 by 5 grid works surprisingly well. Here is the top-left portion:



I love how the diagonal white line on the left travels across the tiles.

I assumed there would be mostly awful matches, cause y'know, what's the chance you've got an image with the proper colours in most of the parts of the tile? But the vector comparison choses the best fit overall, and 10,000 photos help. We're working on getting that to 30,000 or more.

This is the original photo, which I took in a huge indoor market in Budapest from melted_snowball's and my trip in 2003.



We're using Flickr's public API and only grabbing thumbnails, each only 1 or 2k, so it's not even a resource-hog. And the mosaic generation is quick- this image took me about 30 minutes to generate on an 800mhz computer.

We could've used ImageMagick as many of the other simple mosaic programs out there do, but we liked the interface of GD much better and it does everything we need for this. So- thanks boutell!!

Comments

Re: YUV!

[chezmax]

You've forgotten to log in.

YUV as described in Wikipedua has the same equations as the Jpeg YCbCr (which is the very last box in the wikipedia YCbCr article.

In the YUV article they're treated as floating point numbers between 0-1.
In the YCbCr, they're treated as 8 bit numbers.

This is the relevant bit:

Y' =       + 0.299    * R'd + 0.587    * G'd + 0.114    * B'd
Cb = 128   - 0.168736 * R'd - 0.331264 * G'd + 0.5      * B'd
Cr = 128   + 0.5      * R'd - 0.418688 * G'd - 0.081312 * B'd

Either way, you shouldn't have too much difficulty with it, and it's likely to be much more useful than HSV. :)