STV3550 datasheet(44/144 Pages) STMICROELECTRONICS

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STV3550

Graphics Functional Description

In this case, the OSD consists of 2 different images which are displayed one after the other at a rate

of 50 images per second. The human eye is able to detect the appearance and disappearance of

both these images in the OSD. This effect is known as “flicker”.

Flutter problems occur when the same image is used in both the top and bottom fields of a single

frame. The top field is displayed in the same position as the bottom field.

In this case, the OSD consists of top field lines and bottom field lines which are displayed one after

the other at a rate of 50 images per second. The OSD image seems to move up and down. This

effect is called “flutter”.

Anti-Flicker and Anti-Flutter filter modes may be applied to Alpha and RGB color values stored in

the CLUT. The filter mode is selected by bits FM[1:0].

Note:

The Anti-Flicker and Anti-Flutter filters are exclusive and cannot be used simultaneously.

Anti-Aliasing Mode

Anti-Aliasing mode is used to smooth and remove the effects caused by insufficient sampling or

poor filtering of the video signal. To enable Anti-Aliasing mode, reset the BDWOFF bit in the

OSD_CONFIG register. The Anti-Aliasing value is stored in the BDW[7:0] bits in the OSD_CONFIG

applied to all OSD regions displayed in the entire frame.

Gain and Offset Operations

A gain value may be applied to RGB outputs after the filter operations for the current OSD region

by setting bit GaEn. This value is always associated with an offset value. 64 gain values are

available by setting bits Gain[5:0]. The gain is never applied to Alpha or 1-Alpha values. The offset

added to the RGB outputs after the gain operation for the current OSD region is defined in bits

Offset[9:0]

R[9:0] = Gain[5:0]/32 x R[9:0] + Offset[9:0]

G[9:0] = Gain[5:0]/32 x G[9:0] + Offset[9:0]

B[9:0] = Gain[5:0]/32 x B[9:0] + Offset[9:0]

Figure 33: Filter Modes

OSD Region

Flicker

Flutter

STV3550 数据表(PDF) 44 Page - STMicroelectronics