Shapes may be stars, polygons, or text. The polygons can be rectangles in which case the software aligns them horizontally to give a tile effect.

Colours are chosen first based upon RGB values of each pixel, if that colour is already used the nearest colour in numeric terms is found; because of the way that RGB is organised as a number (i.e.red × 65536 + green × 256 + blue). this means when looking for nearest match looking through the blues first, then the greens, then the reds. Pixels are looked at starting with the central pixel and working round in an anticlockwise direction. The central pixel therefore will be the original from the photo, because the colour hasn’t been used yet. To prevent this making an original colour block in the centre of the picture, the path is followed in phases, the number of phases being specified by selection.

There is the option of leaving black, white, or grey between specified brightness ranges transparent.

This page is related to my page Equivalent Colour Brightnesses, looking at the effects of equal or close brightnesses on colour perception.

An SVG file is a text file in XML format with no checksums so is easy to modify, in principle. Fill and stroke colours are defined using stylesheets, inline styles, or the SVG parameters fill, stroke, fillStyle and strokeStyle, so straightforward to modify.

The Javascript for this page takes each of the fill and stroke definitions of the input file in turn and modifies according the the criteria chosen by the various options. Colours are converted to hexadecimal format if they are in CSS RGB format, for reduced complexity in processing.

For the Reduced Colour Set option, each of the picked up colour styles is matched to the picked colours and the nearest is chosen to replace the each colour definition. Nearest is on brightness, each matched separately by percentage difference and the lowest of the aggregate of the three percentages is chosen.

The result is an SVG file that can be downloaded, it is also loaded into an HTML Canvas element so can be downloaded as a png-format file.

I wrote this some time ago, it’s one of my earlier experiments and I was never quite sure of the point of it, but have kept it going as it can make some interesting effects.