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.

V16H264Contrast

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.

V16H264Brightness

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.

V16H264LuminanceOutputRange

Luminance output range

The range of luminance output is divided into three regions, as shown in the above drawing.

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).