VX6953CB datasheet(72/107 Pages) STMICROELECTRONICS

72 / 107 page

EDOF control

VX6953CB

72/107

8209023 Rev 5

8.3.1

EDoF_Mode (0xB80)

The EDoF block can be disabled or enabled. The interest of disabling this block would be to

save some power consumption. When enabled, EDoF has two modes:

•

Estimation mode

This mode is dedicated to image preview (Viewfinder) only. EDoF correction is not

applied but statistics are gathered for distance estimation. Estimation mode can be full

resolution, subsampled or binned image up to a maximum of x4 in both directions. If

too much subsampling is performed the image out of the sensor becomes sharp and

focus distance estimation is not possible. This is similar to the mechanical auto focus

control which requires an image large enough to allow detecting sharpness variation

with focus.

ISP should therefore ensure that at least the last frame before capture is set to either

one quarter of the full resolution in each direction or a higher resolution.

In other words, as an example, this means that the minimum input image size when no

crop is applied on the sensor is approximately 640 x 480 for a 5 Mpixel sensor.

•

Application mode

This mode is for capture (or snapshot) mode. The EDoF distance calculated during

estimation is applied to the image. The application mode can only be enabled after the

estimation mode has been selected, otherwise the EDoF correction will not be applied.

EDoF cannot be applied to subsampled or binned images as it is not necessary to

correct images when they are subsampled as the image blur introduced by the lens

does not need to be corrected when images are downscaled. No focus distance

estimates are performed in application mode, even in multi-shot mode.

For preview mode, set the 0x0B80 register in estimation mode:

0x0B80 = 0x02; // EDOF enabled for estimation mode

For capture mode, set the 0x0B80 register in application mode:

0x0B80 = 0x01; // EDOF enabled for application mode

Note:

Before enabling application mode, estimation mode has to be applied for a minimum of one

frame so as to estimate the EDoF focus distance. This information is used in application

mode when the image data is corrected. If estimation mode is not enabled prior to

application mode, no correction will be applied to the captured image.

0x0B88 Hi

edof_focus_distance

16UI

00.32

Value supplied by the host which is

used by VX6953CB for focus distance

(in cm).

0x0000 to 0x7FFF - manual mode

0x8000 to 0xFFFF - limited auto

0x0B89 Lo

0x0B8A

edof_estimation_control

8UI

EDOF estimator control

1 - uniform

2 - centre weight

4 - large spot

8 - narrow spot

Table 41. EDOF registers [0x0B80 to 0x0B8A] (continued)

Index

Byte

Data type Default Type

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