Читать книгу Rethinking Prototyping - Группа авторов - Страница 117

The sample images of the scanned wood types (Meier 2007) are present in the form of JPG files in 8 bit RGB colour. To improve the comparability of the different types and for computational performance reasons, they are first sampled down to a 256 x 256 pixel images. The colour information of every single pixel is then split up in four different two-dimensional dense matrices of double values. The matrices contain the red, green, blue and luminosity value of the pixels colour, mapped to a range from 0 to 1. Luminosity L is calculated as

This conversion into grayscales returns a value much closer to the perceptible “brightness” than the brightness as in a hue/saturation/brightness (HSB) colour model, see Fig. 2.

Fig. 2 Original colour image (left), conversion using brightness (centre), conversion using luminosity (right)

In HSB, the brightness is defined as the biggest of the three-colour channels and stands technically for the voltage needed to display the colour on a screen. In the Venn-diagram above, one of the channels is always 255, therefore the conversion returns all white.

Therefore, 256 x 256 x 3 (the fourth being calculated from the other three) means many data (196’608 floating point values) but not much meaning yet. The questions now are: Which are the most important ones? How do they – or at least some of them – relate to and depend on each other? Are there redundancies that one could get rid of?