STV0974 datasheet(50/69 Pages) STMICROELECTRONICS

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STV0974

Functional description

Note:

If the scaling factor it too high and the cropped image size is bigger than the full source image, the

scaling factor is automatically set to the closest possible high value.

MMS Downscale zoom

This section contains an example of how the low level scalar registers can be used to implement a

down scale ‘zoom’ feature suitable for MMS applications. The example assumes that the desired

output image size is 160 x 120 pixels. The choice of output image size will limit the number of

scaling options available. In this example we are able to select scaling factors 1, 1.5, 2, 2.5, 3 and 4.

The source image from which the scaled output images are derived is always the full VGA array,

640 x 480 pixels.

If a smaller output image is chosen, 96 x 80 for example, then clearly the entire scaling factor range

would be available.

With reference to the example below (

Figure 29), a scaling factor of 4 actually yields a ‘zoom’ of 1.

This implies that the full scene field of view is preserved within the output image but heavily scaled.

To ensure that the smaller scaling factors produce the same output image size it is necessary for

the video processor to crop the source VGA image prior to scaling. This has the effect of limiting the

scene field of view but yields the ‘zoom’ effect.

Still / Live Scaling

factor

0x806D

R/W

RRRR.RDDD

0000.0001

Scaling factor in Still/Live:

0: Reserved

1: x1 (Default)

2: x2

3: x3

4: x4

5: x5

6: x6

7: x1.5

8: x2.5

Table 34: Scaler low-level control

Name

Index

R/W

State

code

Data

type

Format

default

Description

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