Vectorscope

Vectorscope

Evaluation scale on the vectorscope

A vectorscope (often also referred to as vectorscope ) is a measuring device that is primarily specialized for video technology . In analog television technology, image signals are transmitted using vector modulation , which is difficult to view with a conventional oscilloscope . The vectorscope, on the other hand, enables a specialized representation of the color vectors. The main application of a vectorscope is color matching and the analysis of image quality. The vectorscope is also useful for the analysis of copy protection processes in video technology, as these are mostly based on a manipulation of the color vectors. Measuring devices for the investigation of digital modulation methods such as a. Used in digital television , on the other hand, are usually not referred to as a vectorscope, but rather as a vector analyzer.

As vectorscope also is goniometer (stereo vision device) designated in audio engineering.

functionality

In older devices, the color vectors are displayed optically in a circular scale with the aid of a cathode ray tube . Measuring devices commonly used today calculate the vector display in real time using software and are usually equipped with LCD screens to display the results .

The color difference signal (RY) (red minus lightness) is plotted in the vertical direction and the color difference signal (BY) (blue minus lightness) in the horizontal direction. Except for constant factors, these color difference signals correspond to the U and V signals in the YUV color model . The two color difference signals are determined from the RGB color space according to the EBU specification with the following equations, where R stands for the color value red, G for green and B for blue:

${\displaystyle (R-Y)=0,701\cdot R-0,587\cdot G-0,114\cdot B}$

${\displaystyle (B-Y)=-0,299\cdot R-0,587\cdot G+0,886\cdot B}$

The following relationship is used to determine the two color values U and V :

${\displaystyle V=(R-Y)\cdot 0{,}877}$

${\displaystyle U=(B-Y)\cdot 0{,}493}$

In television technology, the reduced color difference signals U and V are processed directly for the X and Y deflection , with U being plotted on the X axis and V on the Y axis.

The greater the saturation of a color, the further out the mapped color locations are. Achromatic tones result in a point in the middle of the screen (black / white / gray values). A color can be defined by specifying two values ​​(angle on the vectorscope) and color saturation (distance from the center of the scale).

The lines named I and Q denote the color axes of the YIQ color model . Since skin tones are usually on the I-line, this is displayed as a reference for color correction, because skin tones that deviate greatly from this line appear unnatural to the human eye.

Web links

• Vectorscope with the U and V chrominance signals (Flash)
• Introducing Color Scopes: The vectorscope ( Memento of 22 March 2016 Internet Archive ) - An Introduction to vectorscope (English)

Individual evidence

1. ↑ Vectorscope: What the I and the Q lines are good for ( Memento of the original from December 1, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.