Runco REFLECTION CL-510 Manual de usuario descargar pdf (Pagina 20)

TECH CORNER

20 ExtroNews 14.3 Fall 2003

Consider Figure 5, which shows the

second source from Figure 1 being scaled. In

this example the signal of a PC is delivered

at 1024 x 768 to an Extron ISS 408, then

to a projector at 1024 x 768. This example

represents one of the greatest challenges that

a scaler can meet head on, delivering one

pixel out for one pixel in, or as many pixels out

as in. It is accomplished by the scaler in this

example by sampling one pixel on the input

for each pixel output.

Clock, or pixel clock as it is sometimes

called, can be adjusted in a number of

different ways. In the ISS 408, adjusting the

horizontal size is done by changing the

number of samples taken across a given time

of active video, as shown in Figure 5. If the

number is increased the image gets smaller,

and vice-versa. By adjusting the size in this

way, the scaler is also adjusting the clock, or

the number of samples per pixel.

Figure 5 also demonstrates an additional

impact of adjusting the size in this way. The

lower image in each section of Figure 5

shows an oscilloscope readout of the number

of pixels sampled on the input versus the

number generated on the output. The top

image in each section shows the resulting

image, and in some cases the artifacts that

occur as a result of the clock speed. The test

pattern is a pixel on, pixel off pattern, where

every other pixel is turned on, and then off,

and can be generated in many ways with

computers or test generators.

Current technology allows for clock speeds

that sample at a rate of one sample per pixel.

Over sampling, or taking many more samples

than there are pixels, would be preferred,

however IC performance and cost currently

limit most scaler technology to 1:1 sampling

Optimizing Your Image with Auto-Image (continued)

Sample

points

H-line

Pixel on

Pixel off

Figure 5-1: Sampling

1 sample / pixel

Figure 5-2: Under sampling

Too few samples / pixel

Sample

points

H-line

Pixel on

Pixel off

Figure 5-3: Over sampling

Too many samples / pixel

V-Sync

Field

of Video

Figure 4-2: Correct image size

768 lines with correct vertical time frame

Figure 4-1: Image too tall

768 lines with too wide a vertical time frame

768 lines in correct

vertical time frame

768 lines in too wide

a vertical time frame

Figure 4: How a scaler corrects vertical image size.

Figure 5: Examples of correctly clocked, under clocked, and over clocked signals.

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