AL250 International Power Sources, Inc., AL250 Datasheet - Page 16

• Manufacturer Part Number: AL250
• Description: Video Scan Doubler
• Manufacturer: International Power Sources, Inc.

AL250
External overlay applies to the AL250/251 analog output and the AL251 digital RGB output, but not
to the AL251 digital YUV output.
6.7 Look-up Table (LUT)
Because of the different characteristics of TV’s and PC monitors, direct color space conversion from
TV to PC may not show the same color that the human eye sees from the original video on the TV.
The contrast may not be sufficient, and the hue may not be accurate, so to resolve these issues the
AL250/251 has a gamma correction internal LUT implemented.
The AL250/251 provides 768 registers for implementing the LUT. The directly converted colors are
sent to the LUT that then sends out the mapped, corrected colors. To program the LUT, first choose a
color (R, G or B) from register 10h, select the LUT index (0~255) through register 11h, then fill the
data (0~255) through register 13h. The input 8-bit R (or G or B) value is then converted to the
corrected R (or G or B) value.
The user can program the LUT based on his/her own experiments on specific types of monitors. The
typical input-output mapping curve is usually somewhat like the following:
Output
Corrected
Conversion
Direct
Conversion
Input
LUT control applies to the AL251/251 analog output but not to the AL251 digital YUV/RGB output.
2
6.8 I
C Programming
2
2
The AL250/251 I
C programming interface follows the Philips standard. The I
C interface consists of
the SCL (clock) and SDA (data) signals. Data can be written to or read from the AL250/251. For both
read and write, each byte is transferred MSB first, and the SDA data bit is valid when the SCL is
pulled high.
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July 28, 1999