HMP8112 Datasheet, PDF (10/40 Pages) Harris Corporation – NTSC/PAL Video Decoder

HMP8112
flag, when asserted, tells the user that the video standard
that was expected was not found and a different standard
should be selected in the Video Input Control register. The
error flag is cleared after a RESET or after the Chroma PLL
Clock Ratio register has been loaded via the I²C bus. After
the flag is cleared the standard error logic verifies the video
standard. The error flag is set after 2 vertical sync periods
have passed and the line count did not match the expected
line count.
Video Adjustments
The HMP8112 allows the user to vary such video parame-
ters as Contrast, Brightness, Sharpness, Hue and Color Sat-
uration. These adjustments can be made via the I²C
interface. Contrast, brightness and sharpness are luminance
controls. The full dynamic range of the luminance channel
can be used by selecting the IRE setup cancellation mode.
This mode will remove the IRE setup and blanking level off-
set to take advantage of the full dynamic range of the lumi-
nance processing path. The sharpening filters allow the
enhancement of low, mid and high frequency components of
the luminance signal to compensate for low amplitude video.
Vertical sharpness is also controlled via the I²C interface.
Hue and Color saturation controls enhance the CbCr com-
ponents of the incoming video, all under user control.
TABLE 3. USER CONTROLLED SETTINGS
USER VIDEO SETTINGS
Brightness
Contrast
Hue or Tint
Horizontal Sharpness
Vertical Sharpness
Color Saturation
Luminance Adjustments
The Luminance data can be adjusted in the HMP8112. The
user can adjust brightness and contrast of the Y or lumi-
nance data. The user can also set the IRE or setup subtrac-
tion value to eliminate the black pedestal offset from NTSC
signals. The Contrast adjustment range can exceed a value
of one so as to take full advantage of the 8-bit dynamic
range for Y. The user control settings executes the equation
Brightness
The user can control the brightness of the incoming video by
programming the Brightness register. The brightness adjust-
ment will offset the Y component. The brightness register is
an 8-bit register where the bottom 7 bits are brightness con-
trol and the top bit is the IRE setup. The IRE setup for NTSC
is 70 and the setup for PAL is 63.
When the IRE bit is set (1) then the value of 70 is subtracted
from the Y data, and if the IRE bit is cleared (0) then the val-
ues of 63 is subtracted. The brightness control bits BR[6-0]
will brighten the picture as the value is increased. BR = -64
is the darkest and BR = +63 is the brightest. The default
value of the register after a RESET is 0 (80_H).
Contrast
The contrast adjustment will allow the user to increase and
decrease the gain of the Y data. The contrast factor is an 8-bit
number (as shown below) that ranges from 0 to 1.999.
X.XXXXXXX
The default value after a RESET is 1.47 (BD_H).
Hue or Tint Adjust
The Hue adjustment is applied to the U and the V color differ-
ence signal. The Hue adjusts the phase of the given UV data.
The Hue can be adjusted by ±30^o in 1/4^o increments. This is
achieved by changing the Burst Phase Locked reference
point. Figure 10 shows the block diagram for the color adjust-
ment section. This default value for this register is 0 (00_H).
VIDEO
DATA
DEMODULATED
COLOR
UV DATA
DECODER
CHROMA
AGC AND
USER
SETTINGS
HUE OFFSET
UV DATA
+
HUE
ADJUST
TO INPUT SAMPLE
RATE
CONVERTER
CHROMA
PHASE LOCKED
LOOP
Y_OUT = (Y - IRE Setup + BRIGHTNESS) x CONTRAST
BRIGHTNESS
(-64 TO +63)
FIGURE 10. HUE ADJUST BLOCK DIAGRAM
Horizontal/Vertical Sharpness
Y DATA ₊
FROM
DECODER
-
+
X
Y’
8
IRE BLACK SETUP
(NTSC = 70, PAL = 63)
CONTRAST
(0 TO 1.999)
FIGURE 9. LUMINANCE CONTROL SETTINGS PATH
The frequency characteristics of the video waveform can be
altered to enhance the sharpness of the picture. The Horizontal
Sharpness register acts as a 4 band equalizer where the ampli-
tude of specific frequency ranges can be enhanced or dimin-
ished. The Sharpness Control Register allows the Low (LF),
Mid (MF) and High Frequency (HF) bands of the luminance sig-
nal to be enhanced. Vertical Sharpness can be adjusted to 1 or
a factor of 0. The RESET default is a factor of 1.0
10