The gray value referred to in typography as in image processing, the apparent brightness of a text or an image or a single pixel. He thus indicates how light or dark the object in question appears to the human eye.
In the typography
In typography, the gray value is mainly determined by stroke width, spacing, word spacing, line length and line spacing or line penetration. Ideally, all of these features are matched to each other so that the text is perfectly legible.
The gray scale value can then be used in a threshold method, for example, for comparison with a threshold value.
In image processing,
In image processing, the gray value of the brightness or intensity value of a single pixel dar. In the case of an RGB color value can be represented by the formula
The gray value are calculated. The result is a value that represents, regardless of the colors, the brightness of the pixel. The percentage distribution of colors is related to the corresponding color sensitivity of the eye. In the image processing practice, this distribution is, however, sometimes disregarded and all three color channels are weighted equally.
In the television industry, the gray level signal (luminance signal) is still used in the composite signal to the old composite video signal ( black / white) to be compatible.
Grey color image with channel weighting
Grey color image without channel weighting