TMC22091 datasheet(40/60 Pages) CADEKA

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TMC22091/TMC22191

PRODUCT SPECIFICATION

Layering with the TMC22191

Layering is a video production process where various images

or patterns are superimposed (keyed) over each other to form

a layered composite of the input images. Four layers with the

following priority are provided by the TMC22191:

The DOWNSTREAM KEY layer keys over all other

layers.

The FOREGROUND layer keys over MIDGROUND

and BACKGROUND, but not over DOWNSTREAM

KEY.

The MIDGROUND layer keys over BACKGROUND,

but not over FOREGROUND or DOWNSTREAM

KEY.

The BACKGROUND layer never keys over any other

layer.

It is important not to confuse layers with sources. The

TMC22191 can be programmed to assign any of its input

sources (RGB, YCRCB, CVBS bus, Overlay bits) to any of

the four layers.

The ability to combine various video sources into a 4-layer

composite image is a very powerful tool in the production of

live video. The TMC22191 performs layering operations

entirely in the digital domain, enabling precise digital

control.

A 4-Layer Example

For this layering example, a BACKGROUND image is

generated. This image comprises shaded matte levels varying

from black at the top of the screen to white at the bottom.

This could just as well be a color image which will be seen

wherever no other image appears through the layering

process.

The MIDGROUND image comprises a happy face superim-

posed over a white rectangle. Only the happy face and the

white rectangle are of interest for this image and therefore,

the portion of the image outside that area will be replaced by

the BACKGROUND image when MIDGROUND is keyed

over BACKGROUND. A key signal is generated on a pixel-

by-pixel basis. It indicates which image is active. The key

signal for keying MIDGROUND over BACKGROUND is

shown to the right of the MIDGROUND image. This repre-

sents a single bit signal mapped over the image. When the

signal is black (logic LOW), the MIDGROUND image is

active, when it is white (logic HIGH), the BACKGROUND

is active.

The results of layering MIDGROUND over BACK-

GROUND images are shown in the 2-layer composite image

Figure 19.

Figure 19. 2-Layer Image Construction

BACKGROUND

MIDGROUND

KEY

2-LAYER COMPOSITE

27036A

A FOREGROUND image comprises a shaded matte rectan-

gle with "HI KIDS !" alpha characters in its center. This is to

be superimposed over the previous 2-layer composite image.

The key signal needed for superimposing FOREGROUND

over other images is shown to the right of the FORE-

GROUND image. This represents a single bit signal mapped

over the image. When the signal is black (logic LOW), the

FOREGROUND image is active, when it is white (logic

HIGH), the composite image is active.

A new 3-layer composite image, FOREGROUND over

MIDGROUND over BACKGROUND, is shown in Figure

20.

TMC22091 Datasheet(PDF) 40 Page - Cadeka Microcircuits LLC.

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