Image courtesy of Megapixel
Colour printers use some number of inks or pigments for subtractive colour synthesis. However, most consumer and office printers are designed to accept sRGB encoded colour data. Conversions from sRGB to the native printer colour encodings are performed in the printer or printer driver.
Because the printed media is almost always quite different from the sRGB reference display, printer colour conversions almost always include significant colour re-rendering. The purpose of this re-rendering is to take images that are optimized for viewing on the reference sRGB display, and re-optimize them for the print media to be used. The colour re-rendering is typically accomplished using proprietary algorithms (or even handcrafted colour maps), as the quality of the re-rendering significantly impacts the quality of the final printed images, and is therefore a product differentiator.
The IEC has specified colour data for measurements, sampling of successive prints, measurement conditions and forms of reporting the results to qualitatively characterize colour printers and to compare measurement results. This facilitates communication of the differences between reproductions of sRGB image data as produced by different printers.