Line frequency
The line frequency or also horizontal frequency indicates the repetition rate of lines (horizontal "lines") in a video signal or on a display device (e.g. computer monitor). It is calculated from the displayed full images per second multiplied by the number of lines in a full image. In addition, there may be an overscan and the blanking interval . The horizontal frequency is usually specified in kilohertz and is often abbreviated as HSync or H.Frequency .
calculation
Full screen process
A full image is created with each image transmission according to the vertical frequency ( non-interlaced ):
- The monitor has the properties of 1024 × 768 at 60 Hz.
- Refresh rate × number of lines = line rate
- 60 Hz × 768 lines = 46080 Hz
This corresponds to a line frequency of 46.08 kHz. The number of lines (768 in the example calculation) is the sum of the visible lines and the lines of the vertical blanking interval.
Field method
A full image only arises from the transmission of two fields according to the vertical frequency ( interlaced ):
Using the example of a PAL standard television with 768 × 625 at 50 Hz.
Thus, this television shows 25 full frames per second. This television has 49 blanking lines which, as a ratio to the 576 lines shown, means a blanking time of slightly more than 8.5 percent.
- (Refresh rate / 2) × (number of lines + blanking lines) = line rate
- (50 Hz / 2) × (576 + 49 lines) = 15625 Hz
- Frame rate × number of lines × blanking time (> 8.5%) = horizontal frequency
- 25 frames / s × 576 vertical number of pixels × (1.0 + 0.0850694444) = 15625 Hz
This corresponds to 15.625 kHz.
The reason is that the electron beam only reproduces every second line per image cycle.
- 1. Hz = line 1, 3, 5, ...
- 2. Hz = line 2, 4, 6, ...
This is done because the image is built up 50 times in one second - even if only every second line alternates. This results in an effective image refresh rate for the eye of 50 (half) images per second, which considerably reduces the impression of flickering without the need for a higher line frequency than with 25 full images per second.
Disambiguation
Case full screen :
(Vertical frequency = refresh rate = refresh rate = field rate = fields per second = FPS = frames per second = images per second = full images per second = frame rate = frame rate = frame rate)
Case field :
(Vertical frequency = refresh rate = refresh rate = field rate = fields per second)
/ 2 =
(FPS = frames per second = images per second = full images per second = full frame rate = frame rate = frame rate)