User's guide / Mark #2: readability of text on the background
The calculation of this mark is based on the theory that sets the threshold
difference in brightness and color of the text relative to the background, above which the human eye well perceives the text.
The threshold difference between text and background brightness is 125 units.
The threshold difference between text and background colors is 500 units.
The program analyzes the entire text on a web-page and is building two histograms:
- dependence of the amount of text on a web-page on the difference between the brightness of the text and background behind the text
- dependence of the amount of text on a web-page on the difference between the color of the text and background behind the text
If there is more textual information on the web-page with a high difference between brightness/color of text and background,
then the right and above will be located bars on the histogram and the higher will be mark for this criterion.
It should be noted that the program analyzes each point of the graphic fonts. And if the font has a high degree of smoothing, the
respectively, has greatly blurred the edge of the text letters. And the difference of brightness of these points on the edges of the letters
relative to the background is usually low. Therefore, the use of fonts with a large smoothing leads to a decrease in the mark.