MB87P2020 Datasheet, PDF (172/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

MB87J2120, MB87P2020-A Hardware Manual
Luminance … _{Y 2i – 2}
Y_{2i – 1}
Y _2i
Y_{2i + 1}
Y_{2i + 2}
Y_{2i + 3}
…
Chrominance … _{U2i – 2 U-----2---i--–---2----+-----U----2--i U2i U-----2---i--+-----U-----2---i--+---2- U2i + 2 U-----2---i--+---2----+-----U-----2--i--+----4} …
2
2
2
… _{V 2i – 2 -V----2--i---–---2---+-----V-----2--i}
2
V _{2i -}V_{----2--i---+-----}V_{----2---i--+---2-}
2
V_{2i + 2}
V_{-----2--i---+---2----+----}V_{-----2--i--+----4} ^…
2
Figure 3-6: Pixel structure after linear chrominance interpolation
3.7.2 Matrix Multiplication
GPU incorporates a YUV to RGB Matrix with prebiasing to convert pixels in YUV (YCbCr) color spaces
to RGB color spaces. To flexibly adjust to different input standards, all matrix coefficients can be config-
ured. The following equation is calculated for the YUV to RGB conversion:


R_mtx




C _YR
C _UR
C _VR




Y + PreBias_Y




G_mtx


=


C _YG
C _UG
C _VG


×


U
+
PreBias_U


(6)
 B_mtx   C_YB C_UB C_VB   V + PreBias_V 
All matrix coefficients C_ij are derived from their respective configuration registers P_ij in either of the fol-
lowing ways:
a) Chroma coefficients for green channel C_UG and C_VG :
C_ij = –(P_ij ⁄ 128)
(7)
b) all others:
C_ij = (P_ij ⁄ 128)
(8)
That is, all configuration registers are treated as 8 bit unsigned binary numbers, thus resulting in a range of
–2…0 for coefficients C_UG and C_VG and 0…2 for all other coefficients. All PreBias values are stored as 8
bit signed binary numbers in their configuration registers (cf. table 4-1).
The calculated intensity values for R, G and B are limited to 8 bit positive binary numbers with values out-
side the legal range being clipped to the respective margins, i.e. underflows (negative values) are mapped
to zero, overflows (values >255) to 255.
Note: There is only one set of matrix parameters (pre biases and coefficients) for all layers. YUV color spac-
es with less than 8 bits per channel (i.e. YUV555 and YUV655) are therefore auto scaled to YUV444 in
advance to fit into a unified value range for all YUV color spaces. This scaling works similar to that ex-
plained for the mapping from logical to intermediate color spaces in section 2.3.
3.7.3 Inverse Gamma Correction
When processing YUV material originally produced for display on CRTs color channel intensities are cal-
culated according to equation (6) may be distorted by a gamma function according to (9) to cope with the
non linear electro-optical characteristics of the CRT’s phosphorus.
I _mtx
=
c
⋅
I
γ
act
+
I₀
(9)
with I_mtx being the intensity of one color channel according to equation (6), I_act the actual (linear) intensity,
c and I₀ constants and γ ≈ 2.2 . However, a linear representation (i.e. no gamma distortion) might be de-
manded. Therefore, GPU includes three gamma look-up tables (one per color channel) to accomplish the
inverse transformation to obtain I_act from I_mtx as well as any other (possibly non linear) post-matrix trans-
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