VS6524 datasheet(20/70 Pages) STMICROELECTRONICS

20 / 70 page

Output frame size control

VL6524/VS6524

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6.1.2

Subsampling module

The VL6524/VS6524 has a built in sub-sampler which can divide the image by 1, 2, 3, 4, 5,

or 6.

Using the sub-sampler gives output images with reduced resolution but the same field of

view as the full VGA image or the region of interest defined in the cropping module.

Table 2

lists the available image sizes.

Subsampled images are produced by ‘dropping’ PCLKs so that only certain pixels are

qualified in the output data stream. The figure below indicates a portion of the PCLK

waveform for VGA and QVGA images. The effect of this is that the

time taken to readout one

line of the image remains constant in all subsampled modes - it is just the number of clocks

that changes.

Figure 8.

PCLK waveform in subsampled modes

It is possible to use the crop module and the sub-sampler together to achieve almost any

required image size. When using the crop

and subsampling functions together then the

number of lines in a frame must be an integer multiple of the subsample ratio.

6.2

Frame rate control

The VL6524/VS6524 features an extremely flexible frame rate controller. Using registers

uwDesiredFrame Rate_Num (MSB), uwDesiredFrame Rate_Num (LSB) and

bDesiredFrameRate_ Den any desired frame rate between 1 and 30 fps can be selected

(see

Table 14: Frame rate control for register description). To program a required frame rate

of 7.5 fps the numerator can be set to 15 and the denominator to 2. The default frame rate is

30 fps.

Slower frame rates are achieved by adding interframe lines. This results in a longer frame

period and therefore a longer period over which integration is possible. Due to the longer

Table 2.

Subsampled image sizes

Subsample ratio

Image format

Image dimensions

1 (default)

VGA

640 by 480

2QVGA

320 by 240

213 by 160

QQVGA

160 by 120

SQCIF

128 by 96

106 by 80

D[0:7]

VGA

QVGA

PCLK

Pixel n

Pixel n+2

Pixel n+1

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