VS6955CA datasheet(65/90 Pages) STMICROELECTRONICS

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VS6955CA

Video timing

7.4

Image compression

The objective of image compression is to reduce the required bandwidth in transmission

between the sensor and the host.

The key features of the DPCM/PCM compression algorithm are:

•

visually lossless

•

low cost implementation (no line memories are required)

•

fixed rate compression

The 10-bit to 8-bit DPCM/PCM image compression algorithm is supported by VS6955CA.

10-bit to 8-bit compression has the additional advantage that one pixel value equals

one byte of data.

The level of compression is controlled through the CSI_data_format register. The same

The compression_mode register is used to select which compression algorithm is used.

Currently only the DPCM/PCM technique is supported. Therefore the value of this register is

always 0x01.

The compression_capability register tells the host whether a sensor does or does not have

compression and if it has compression then what is the compression technique. Currently

only the DPCM/PCM technique is supported.

Also refer to section 10 of the SMIA1.0 specification document.

7.5

Exposure and gain control

VS6955CA does not contain any form of automatic exposure control. To produce a correctly

exposed image the integration period and analogue gain for the pixels must be calculated

by an exposure control algorithm implemented externally. The parameters are then written

to the VS6955CA through the CCI interface.

The exposure control parameters available on VS6955CA are:

•

fine integration time

•

coarse integration time

•

analog gain

•

digital gain

The exposure control parameter registers are defined in Section 4.2.6: Integration and gain

registers [0x0200 to 0x0215] on page 30.

Integration time and analogue gain capability registers should be used to determine the

exposure control parameter limits for a given video timing configuration. See Section 6.7 of

the SMIA 1.0 part 1 specification for more information on how to interpret the integration and

gain capability registers and how to calculate exposure and gain limits.

VS6955CA Datasheet(PDF) 65 Page - STMicroelectronics

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