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6. DSP Operation
31
6.7.
Gamma correction
[XCL-5005CR]
[XCL-5005]
Configure each mode with GAMMA-MODE. There is a
method for setting LUT arbitrarily, a method for setting
with approximate linear interpolation, and a method for
setting the gamma curve coefficient. There are seven
gamma modes from Mode 1 to Mode 7. Apart from
Mode 5, which performs LUT initialization to return the
setting to value at the time of shipment, the modes load
the LUT value saved last time and are capable of
accepting a GAMMA command. After you select a
mode with GAMMA-MODE, input a parameter with a
GAMMA command. You can use the RMEM 2
command to read the LUT setting value. When you set
the mode to Mode 5, the setting is returned to the value
at the time of shipment, but due to five-point
approximate linear interpolation performed on the
gamma curve, the setting values of the five points 256,
512, 1024, 2048, and 3072 will be on a curve for which
1, 2, 3, 3, and 3 were selected, respectively.
6.7.1.
Arbitrary setting method
The arbitrary setting method is for inputting an LUT
value for an arbitrary value from 0 to 4095. The relation
of level OUT of the output image to level IN of the input
image is expressed by the following equation.
6.7.2.
Five-point approximate linear
interpolation
This method allows you to set the gamma curve easily
by selecting 1 to 5 for the strength of the output values
for the 5 points 256, 512, 1024, 2048, and 3072 (12-bit
values).
Note
Performing approximate linear interpolation with Mode
2 and Mode 4 may result in a discontinuous curve.
In such a case, gradation parts for which no output level
exists may appear to be missing data after the gamma
process when the video signal is displayed in a
waveform or histogram, but this phenomenon is normal
and not an indication of a malfunction, because there is
actually no video signal output corresponding to such
output steps.
Mode
GAMMA-MODE
operation
Save to ROM
LUT
GAMMA Command
0
OFF (
γ
= 1)
No
Through (
γ
= 1)
Not possible
1
Loads last set value
Yes
Arbitrary setting
Possible
2
Loads last set value
Yes
Five-point approximate
linear interpolation
Possible
3
Loads last set value
No
Arbitrary setting
Possible
4
Loads last set value
No
Five-point approximate
linear interpolation
Possible
5
Reset to initial value
Yes
Value at time of shipment Not possible
6
Loads last set value
Yes
γ
coefficient
Possible
7
Loads last set value
No
γ
coefficient
Possible