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Functional Description (Continued)

3.8.2.4

X and Y Scaler / Filter

The CS5530 supports horizontal and vertical scaling of

the video stream up to eight times the source resolution.

The scaler uses a Digital-Differential-Analyzer (DDA)

baseduponthe values programmedinthe VideoScale

The scaled video stream is then passed through horizon-

tal and vertical filters which perform a 2-tap, 8-phase bilin-

ear filter on the resulting stream. The filtering function

removes the "blockiness" of the scaled video thereby sig-

nificantly improving the quality of the displayed image.

By performing the scaling and filtering function in hard-

ware, video performance is substantially improved over

pure software implementations by requiring that the

decompression software only output the video stream at

the native source resolution. This saves both processor

overhead and memory bandwidth.

3.8.2.5

Color-Space-Converter

After scaling and filtering have been applied, the YUV

video data is passed through the color-space converter to

obtain 24-bit RGB video data. The color-space conversion

equations are based on the CCIR Recommendation 601-

1asfollows:

R = 1.164(Y–16) + 1.596(V–128)

G = 1.164(Y–16) – 0.813(V–128) – 0.391(U–128)

B = 1.164(Y–16) + 2.018(U–128)

The color-space converter clamps inputs to acceptable

limits if the data is not well behaved. The color-space con-

verter is bypassed for overlaying 16 bpp RGB graphics

data.

Table 3-72. Video Scale Register

Bit

Description

F4BAR+Memory Offset 10h-13h

Video Scale Register (R/W)

Reset Value = xxxxxxxxh

31:30

Reserved: Set to 0.

29:16

Video Y Scale Factor: This field represents the video window vertical scale factor according to the following

formula:

VID_Y_SCL = 8192 * (Ys - 1) / (Yd - 1)

Where:

Ys = Video Source vertical size in lines

Yd = Video Destination vertical size in lines

15:14

Reserved: Set to 0.

13:0

Video X Scale Factor: This field represents the video window horizontal scale factor according to the following

formula:

VID_X_SCL = 8192 * (Xs - 1) / (Xd - 1)

Where:

Xs = Video Source horizontal size in pixels

Xd = Video Destination horizontal size in pixels

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