Luminance Processing
The following sections show the functional blocks used for luminance processing.
Contrast
You can adjust picture contrast by applying gain on luminance component through the Contrast element. This contrast control can be used at anytime, even during acquisition. The decoder provides a luminance gain adjustment in 256 steps, ranging from 0 up to 200 %, with a default value of 100 %.
The following figure shows the luminance transfer function for three contrast settings and the nominal brightness setting.
The luminance output span is expressed in 8-bit digital codes according to ITU-R BT.601-4 specification.
Contrast (luminance gain) control
Brightness
You can adjust picture brightness by applying offset on luminance component through the Brightness element. This contrast control can be used at anytime, even during acquisition. Picolo U4 H.264 PCI-104 provides an offset gain adjustment in 256 steps, ranging from -25 % up to 25 % of the output span.
The following figure shows the luminance transfer function for three brightness settings and the nominal brightness setting.
Brightness (luminance gain) control
Luminance Output Range Limiting
The luminance component Y is delivered in 8-bit digital codes, according to ITU-R BT.601-4 specification. The luminance spans over 220 levels, with the black level corresponding to code 16 (0x10), and white level corresponding to code 235 (0xEB). The following diagram shows the luminance output range.
Luminance output range
The range of luminance output is divided into three regions, as shown in the above drawing.
- The super-black region (code from 1 up to 15) and the super-white region (code from 236 up to 254) provide some extra margins for occasional excursion of the signal beyond the normal limits, or for some contrast and/or brightness settings.
- The black-to-white region is the effective luminance output span: a correctly adjusted digital video renderer considers exclusively this region.
The luminance output range is normally bounded in the range [2..254]. The darkest luminance levels will not produce a luminance output code below 2, and the brightest luminance levels will not produce a luminance output code above 254 (0xFE).