Omnivision CameraChip OV9650, Implementation Manual

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14 Proprietary to OmniVision Technologies Version 1.1, December 7, 2004
OV9650 Color CMOS SXGA (1.3 MegaPixel) CameraChip™ O
mni ision
2. Set the C
AMERA
C
HIP
Available Exposure Line (AEL):
Suppose N is integer, N = 1,2,3…
Available exposure line are: AEL = N
×
MEL where AEL should be equal or less than the maximum
exposure line limitation based on different resolutions.
3. Convert AEL to binary, and then send 2 LSBs hex number to register COM1 [1:0] (0x04) and 8 MSBs hex
number to register AECH [7:0] (0x10) and 6 MSBs to register AECHM [5:0] (0xA1).
Maximum Exposure Line Limitation
OV9650 maximum exposure line values are:
• SXGA - 1048 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x01, AECH [7:0] (0x10) = 0x06, COM1 [1:0] (0x04) = 0x00}
• VGA - 498 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x00, AECH [7:0] (0x10) = 0x7C, COM1 [1:0] (0x04) = 0x02}
• QVGA - 248 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x00, AECH [7:0] (0x10) = 0x3E, COM1 [1:0] (0x04) = 0x00}
• QQVGA - 248 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x00, AECH [7:0] (0x10) = 0x3E, COM1 [1:0] (0x04) = 0x00}
• CIF - 382 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x00, AECH [7:0] (0x10) = 0x5F, COM1 [1:0] (0x04) = 0x02}
• QQCIF - 190 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x00, AECH [7:0] (0x10) = 0x2F, COM1 [1:0] (0x04) = 0x02}
• QQCIF - 190 lines
Register setting: {
AECHM [5:0] (0xA1) = 0x00, AECH [7:0] (0x10) = 0x2F, COM1 [1:0] (0x04) = 0x02}
3.4.1.2 Automatic Exposure Control Mode (AEC)
The AEC function allows for the C
AMERA
C
HIP
to adjust the exposure without external command or
control. The registers AECHM [5:0] (0xA1), AECH [7:0] (0x10), and COM1 [1:0] (0x04) are adjusted
by the C
AMERA
C
HIP
internal controls and cannot be overwritten by an external device.
Auto-Exposure Control Enable Bit
To enable the AEC function, set register COM8 [0] (0x13) to "1". The AEC controls image luminance
using registers AEW (0x24) and AEB (0x25). The register AEW (0x24) value indicates the high
threshold value and register AEB (0x25) indicates the low threshold value. When the target image
luminance average value (YAVG) is within the range specified by registers AEW (0x24) and AEB
(0x25), the AEC keeps the image exposure. When YAVG, is greater than the value in register AEW
(0x24), the AEC will decrease the image exposure. When YAVG is less than the value in register
AEB (0x25), the AEC will increase the image exposure. Accordingly, the value in register AEW
(0x24) should be greater than the value in register AEB (0x25). The gap between the AEW (0x24)
and AEB (0x25) register values controls the image stability. The recommended values for register
AEW (0x24) and AEB (0x25) are: AEW (0x24) = 0x74; AEB (0x25) = 0x68.