[bazzargh]

While this is nice enough, it bothers me that these don't look much like "art". If you look at real roman mosaics, they do not place points in a grid - they use a technique called "opus vermiculatum" https://en.wikipedia.org/wiki/Opus_vermiculatum ... snaking the tiles around so that there is a flow to it; the overall effect is much better.

I think that'd be possible to automate too. I was doing something related over here: https://hachyderm.io/@bazzargh/112767548339559102 - in that I was trying to generate sketch-like renderings from photographs. What I did was to pick random points, look at the brightness gradient (taken from the Sobel operator, there are other ways to do this), move up the gradient a bit and sketch some parallel lines (and then various experiments with hatching for shading the flatter areas)

In a similar way you could start with a grid of tiles _with some separation_, and allow them to move and align better with the gradient of the underlying picture, and not lie _on_ edges, if possible. If they overlap, allow the tessera to be cut, and only then choose images to colour-match the average on the tile, leaving some "grout" in the image (I'd probably speckle that a bit so it didn't look too uniform). Then the result might look more like real mosaics.

I might give this a go...

[schwartzworld]

> While this is nice enough, it bothers me that these don't look much like "art".

The author didn't invent this style. The first thing I thought of was the poster for the Truman Show. https://artofthemovies.co.uk/products/the-truman-show-1998-m... The site seems to make that happen quite well.

[bazzargh]

I managed to get some decent results using this algorithm (not at my own computer so can't post code, yet):

- create a smaller greyscale copy of the image, and use sobel to calculate gradients (smaller to speed this up)

- set a gradient magnitude threshold, and add those points to a queue, largest first.

- for these points, add 2 squares, one either side of the queued point, in the direction of the gradient (ie you expect one to be light and one dark)

- add the squares to a location hash as they are placed. (I'm using a grid size slightly larger than my square tiles). The location hash is to speed up comparisons.

- skip placing a square if it would fall within a small radius of a previous square's centre (I used 0.5 of a square size). When looking up a point in the location hash, remember to look not for the point itself, but for the hash values for the corners of an axis-aligned square with your point at the centre; this is to catch overlaps when the point falls need grid lines.

- once all points in this queue have been processed or skipped, we start on a new queue, containing all squares placed so far.

- for each square in the queue, try to place a new square to its north, south, east and west along its alignment; as before skip these if they overlap too much

- any squares we place - jitter their position and angle slightly (otherwise it looks horribly unnatural)

- any squares we do place, add them to the phase 2 queue.

The first phase is quite slow, set the threshold high. Second phase placement is very fast. My squares all use a grey stroke the same grey as the background for the grout effect, and the squares are drawn using the colour of the point picked as the square's centre (I don't bother averaging). I have it rendering this interactively, using requestAnimationFrame, so it doesn't clog up the browser - I add about 50 tiles per frame

I'm looking at one it did of the mona lisa; it places the phase 1 tiles along her hairline and hand in a nice "vermiculatum" way, the phase 2 placement is less satisfying but with jitter it seems ok. Originally I'd thought about calculating where squares overlap and cutting tiles nicely but it was quicker just to _allow_ the overlap and so most of what you see are the whole tiles placed on top of partials. The overall effect isn't _quite_ like hand placed tiles but I like it better than a grid.

You can see a couple of output images here. https://hachyderm.io/deck/@bazzargh/114938616011157584

[Theodores]

Whilst you are at it...

https://github.com/openseadragon/openseadragon

A photo mosaic demands to have photos that are high resolution. You don't want to zoom in to find blurry jpegs, it just isn't right!

I have had great fun with OpenSeadragon in the past and now there is the VIPS image processing library for writing out a massive set of image tiles.

Hence it is possible to work with thumbnails and then render out the thing with OpenSeadragon and VIPS.

OpenSeadragon was amazing when it was a Microsoft demo a few decades ago, but time has moved on. I wonder what can be done with tilesets in HTML5 with picture tags or in SVG to present a infinitely zoomable montage.

I like your suggestion and the options for rotating and clipping images with SVG methods. I always confuse mask and clip, but, in SVG, much could be done.

For me, the starting point would be to do an SVG with thousands of images in it, to just watch my computer crash as I step up the resolution. Really I want to recreate OpenSeadragon in SVG...

[wang_li]

There is a naive approach to making this kind of thing that reduces the component images to such a small size (2-3 pixels in large image) that turns this into more of a dithering exercise than looking for artifacts in each component image to match up lines. It's still a nice effect, but it's quite different when the component images are > 10% the size of the final image, instead of < 1% the size.

[wvlia5]

It could be better sometimes for tiles to lie over edges. For example, there might be an edge dividing red and green areas, and one of your tiles is mostly half red and half green.