SAA7118 Datasheet, PDF (57/169 Pages) NXP Semiconductors – Multistandard video decoder with adaptive comb filter and component video input

Philips Semiconductors
Multistandard video decoder with adaptive
comb filter and component video input
Preliminary specification
SAA7118
8.4.3.2 Vertical scaler (subaddresses B0H to BFH and
E0H to EFH)
Vertical scaling of any ratio from 64 (theoretical zoom)
to ¹â„₆₃ (icon) can be applied.
The vertical scaling block consists of another line delay,
and the vertical filter structure, that can operate in two
different modes; Linear Phase Interpolation (LPI) and
accumulation (ACM) mode. These are controlled by
YMODE[B4H[0]]:
• LPI mode: In LPI mode (YMODE = 0) two neighbouring
lines of the source video stream are added together, but
weighted by factors corresponding to the vertical
position (phase) of the target output line relative to the
source lines. This linear interpolation has a 6-bit phase
resolution, which equals 64 intra line phases. It
interpolates between two consecutive input lines only.
LPI mode should be applied for scaling ratios around 1
(down to ¹â„₂), it must be applied for vertical zooming.
• ACM mode: The vertical Accumulation (ACM) mode
(YMODE = 1) represents a vertical averaging window
over multiple lines, sliding over the field. This mode also
generates phase correct output lines. The averaging
window length corresponds to the scaling ratio, resulting
in an adaptive vertical low-pass effect, to greatly reduce
aliasing artefacts. ACM can be applied for downscales
only from ratio 1 down to ¹â„₆₄. ACM results in a scale
dependent DC gain amplification, which has to be
precorrected by the BCS control of the scaler part.
The phase and scale controlling DTO calculates in 16-bit
resolution, controlled by parameters YSCY[15:0] B1H[7:0]
B0H[7:0] and YSCC[15:0] B3H[7:0] B2H[7:0], continuously
over the entire filed. A start offset can be applied to the
phase processing by means of the parameters
YPY3[7:0] to YPY0[7:0] in BFH[7:0] to BCH[7:0] and
YPC3[7:0] to YPC0[7:0] in BBH[7:0] to B8H[7:0]. The start
phase covers the range of ²⁵⁵⁄₃₂ to ¹â„₃₂ lines offset.
By programming appropriate, opposite, vertical start
phase values (subaddresses B8H to BFH and
E8H to EFH) depending on odd/even field ID of the source
video stream and A/B-page cycle, frame ID conversion
and field rate conversion are supported (i.e. de-interlacing,
re-interlacing).
Figs 35 and 36 and Tables 13 and 14 describe the use of
the offsets.
Remark: The vertical start phase, as well as scaling
ratio are defined independently for luminance and
chrominance channel, but must be set to the same
values in the actual implementation for accurate
4 : 2 : 2 output processing.
The vertical processing communicates on its input side
with the line FIFO buffer. The scale related equations are:
• Scaling increment calculation for ACM and LPI mode,
downscale and zoom: YSCY[15:0] and YSCC[15:0]
=
lower integer
of


1024
×
N--N---l-i-l-ni-n--e--e-_--_--o-i--nu---t^
• BCS value to compensate DC gain in ACM mode
(contrast and saturation have to be set): CONT[7:0]
A5H[7:0] respectively SATN[7:0] A6H[7:0]
=
lower
integer
of


N--N---l-i-l-ni-n--e--e-_--_--o-i--nu---t
×
64_
,
or
=
lower integer
of


Y-----S----C-1---Y0---2-[--1-4--5---:--0---]
×
64_
8.4.3.3 Use of the vertical phase offsets
As described in Section 8.4.1.3, the scaler processing may
run randomly over the interlaced input sequence.
Additionally the interpretation and timing between ITU 656
field ID and real-time detection by means of the state of
H-sync at the falling edge of V-sync may result in different
field ID interpretation.
A vertically scaled interlaced output also gets a larger
vertical sampling phase error, if the interlaced input fields
are processed, without regard to the actual scale at the
starting point of operation (see Fig.35).
For correct interlaced processing the vertical scaler must
be used with respect to the interlace properties of the input
signal and, if required, for conversion of the field
sequences.
Four events should be considered, they are illustrated in
Fig.36.
2001 May 30
57