HD49815TF Datasheet, PDF (14/22 Pages) Hitachi Semiconductor – Digital Camera Signal Processor

HD49815TF
c. RGB-setup block
The black level of the color signals is variable according to the coefficients of the RGB matrix. The value
calculated by the formula below is subtracted from the color signal to correct the black level. The subtracted
value can be set externally and is set in State Data SP_A3 [0 to 2].
Formula = −[48 × Σ (Matrix data) × 2³]
d. RGB-gain block
The RGB gain value acquired in the AWB control is set in the RGB gain circuit to improve the white
reproduction performance. As it is set prior to the gamma correction, it changes the gamma correction amount.
The RGB gain can be set in State Data SP_A3 [3 to 5] from 1 to 256 times. (The G gain is set from 1 to 128
times.)
e. C gamma (γ) correction block
The C gamma correction circuit performs gamma processing on the RGB signal. It is set in State Data SP_A3 [6
to 9]. Four kinds of values can be set independently, according to the input-signal level, to acquire optimal
gamma characteristics: the C gamma dark (to reduce the gain of the small signals for improving S/N), C gamma
coefficient (to control the expansion of the gamma curve), C gamma knee (to decide the slope of the large
signals), and C gamma limit (to perform high-clipping processing for the input signal of the C gamma circuit).
f. YL matrix block
The luminance level changes according to the color temperature of the imaged object. Set State Data SP_A5 [12,
13] for the luminance correction. To correct the luminance, create YL from the three primary colors (R, G, and
B) and convert it to the luminance signal level. The YL matrix circuit creates the YL level from the RGB signal.
The YL matrix is set in State Data SP_A3 [11 to 13].
g. The axis-conversion (C-Y matrix) block
The C-Y (color-difference) matrix takes R-G and B-G as its input signals, and creates the R-Y and B-Y color-
difference signals by setting coefficients for those inputs.
The axis-conversion (C-Y matrix) circuits are set in State Data SP_A8 [0 to 5].
h. Base-clipping block
Since base clipping is performed on the color-difference signals, the base-clipping circuit has the characteristics
of clipping the sections near axes on a vector scope.
This circuit is set in State Data SP_A8 [8].
3. Luminance-signal-processing block
From
the input
line
memory
block
from
YL matrix
H.V
enhancer
Luminance
correction
+
Gamma
correc-
tion
Highlight
enhancer
To
the AWB-
detection block
Fade +
To
the zoom
function
Y Setup
7.5IRE
Figure 5 Luminance-Signal-Processing Block
a. H-enhancer function
The H-enhancer circuit allows the core level, the enhancer gain, and the noise coefficient to be set independently
to acquire optimal characteristics.
This circuit is set in State Data SP_A4 [4 to 7].
b. V-enhancer function
The V-enhancer circuit allows the enhancer coefficient to be set and can control the gain for only those signal
components that exceed the set core level.
This circuit is set in State Data SP_A4 [8 to 10].
c. Luminance correction
The ratio of the red and blue levels changes according to the color temperature of the imaged object. For
example, if a red object is imaged at a low color temperature, the luminance level increases and the object
appears to have a lower chrominance. Therefore, the luminance correction circuit performs luminance-
correction processing to implement color depth reproduction.
The luminance-correction circuit is set in State Data SP_A5 [12, 13].
Rev.1.00 Jun 15, 2005 page 14 of 21