Luminance
The luminance is a photometric size of video technology , as a measure of the brightness of pixels is used. Physically it corresponds exactly to the luminance with the unit cd / m². The term “luminance”, however, connotes the special context of video technology and that calculations are usually made in units of maximum luminance. In addition, luminance is a transmitted signal that ignores the directional dependence of luminance and is only proportional to luminance if the screen is optimally calibrated .
The English term luminance stands for both luminance and luminance, which can lead to translation errors.
The terms luminance signal and luma are used for both analog and digital image data . The word "Luma" was introduced in 1953 by the NTSC . Luma corresponds approximately to the brightness ( brightness ), but is often mistakenly referred to as the video area luminance.
The luminance signal E ' Y is calculated from the pre - equalized non-linear color value signals E' R , E ' G and E' B as follows:
- E ' Y = 0.299 E' R + 0.587 E ' G + 0.114 E' B . (Rec 601)
Luma (the Y component in YUV and YCbCr ) is a weighted sum of non-linear RGB components (i.e. R'G'B 'signals) after applying a gamma correction . Weighting in digital PAL and NTSC systems (YCbCr according to CCIR 601 ), in HDTV systems (e.g. ITU-R BT.709) and in other JPEG or MPEG -based digital image and video systems (e.g. B. DVD-Video ):
- Y '= 0.2126 R' + 0.7152 G '+ 0.0722 B'. (Rec. 709)
Flickering of image sequences can result from incorrect luminance or luma setting or conversion.
In a digital 8- bit - coding , there are 2 8 = 256 different shades of gray, d. H. Black, white and in between 254 shades of gray .