PixArt Imaging Inc.

PAC207BCA

Single-Chip CIF CMOS Image sensor with USB

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6

V1.3, June. 2004

5.2 IMAGE COMPRESSION

PAC207B utilize the PixArt proprietary compression algorithm to maintain the balance

between image quality and frame rate. PAC207B also supported a unique frame sync & frame

header identity, which indicates the frame start information and the frame properties, then

followed a compressed data line by line.

Operation Modes

1. Excellent Quality

2. High quality

3. Normal quality

4. High compression

5. Bandwidth release

Decisionpriorityof compressionmodeselection

The PAC207B utilized a multiple mode image compression algorithm with an advanced rate

control scheme to get the best image quality under different USB bandwidth or image

complexity. By setting the register of address 66~74, the PAC207 can adjust the data rate of

compressed image date while maintain a good image quality. When CMOS sensor running at

a slow frame rate as low-luminance condition, the compression can easily switch to raw data

mode, which has minimum compression errors.

5.3 USB VIDEO ISO_IN ALTERNATE SETTING

Alternate setting

0

1

2

3

4

5

6

7

8

Max packet size (Bytes)

of ISO-IN pipe

0

128 256 384 512 640 768 896 1023

When the device is plugged, the driver will allocate bandwidth by USB host controller status.

The “Alternate setting” and “Max Packet size of ISO-IN pipe” will be set as much as possible

depend on the available bandwidth .The alternate-setting table is shown all bandwidth option

above.