# Make an image from image tiles

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### Question

I have seen a couple of images where they generally make a face out of numerous smaller images.

For example, say they tile 100 images in 10x10 grid, and somehow they vary hue/sat/col of the smaller images so that when you see the Big Picture, you see another image.

The question boils down to - say you have an image. What kind of algorithm would you apply to that image so that the average RGB value of that image is the one you have defined?

### Solution

1. Calculate the hue/sat/value of every tile (use HSV because smaller differences here seem more "natural" to the human eye than in RGB space)
2. Now calculate the same values for each n*n tile of your big picture
3. Find the tiles with the closest HSV values (minimum of `sqrt((h1-h2)^2 - (s1-s2)^2 - (v1-v2)^)`) and stamp that tile scaled down to n*n into the result.

To find the HSV for a tile, it should be enough to sum up all RGB values and then divide them by the number of pixels and convert that final RGB triple into HSV. But to be save, I suggest that you try that both versions.

See which Wikipedia article for RGB <-> HSV conversions.

To refine the algorithm, you can split every tile into an mm and calculate the average HSV for each grid element. Then, when you look for a match, divide the big image into as usual but also calculate mm HSV values. Select which tile matches most of these m*m best. This allows the algorithm to select tiles which have the same structure as the big picture.

For that extra touch, try to create a gigapixel image.