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PYTHON480 データシート(PDF) 32 Page - ON Semiconductor |
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PYTHON480 データシート(HTML) 32 Page - ON Semiconductor |
32 / 69 page PYTHON 480 www.onsemi.com 32 Automatic Exposure Control The exposure control mechanism has the shape of a general feedback control system. Figure 29 shows the high level block diagram of the exposure control loop. Figure 29. Automatic Exposure Control Loop AEC Statistics AEC Filter AEC Enforcer Integration Time Analog Gain (Coarse Steps) Requested Illumination Level (Target) Digital Gain (Fine Steps) Image Capture Three main blocks can be distinguished: • The statistics block compares the average of the current image’s samples to the configured target value for the average illumination of all pixels • The relative gain change request from the statistics block is filtered through the AEC Filter block in the time domain (low pass filter) before being integrated. The output of the filter is the total requested gain in the complete signal path. • The enforcer block accepts the total requested gain and distributes this gain over the integration time and gain stages (both analog and digital) The automatic exposure control loop is enabled by asserting the aec_enable configuration in register 160. AEC Statistics Block The statistics block calculates the average illumination of the current image. Based on the difference between the calculated illumination and the target illumination the statistics block requests a relative gain change. Statistics Subsampling and Windowing For average calculation, the statistics block will sub−sample the current image or windows by taking every fourth sample into account. Note that only the pixels read out through the active windows are visible for the AEC. In the case where multiple windows are active, the samples will be selected from the total samples. Samples contained in a region covered by multiple (overlapping) window will be taking into account only once. It is possible to define an AEC specific sub−window on which the AEC will calculate it’s average. For instance, the sensor can be configured to read out a larger frame, while the illumination is measured on a smaller region of interest, e.g. center weighted as shown in Table 21. Table 21. AEC SAMPLE SELECTION Register Name Description 192[10] roi_aec_enable When 0x0, all active windows are selected for statistics calculation. When 0x1, the AEC samples are selected from the active pixels contained in the region of interest defined by roi_aec 253−255 roi_aec These registers define a window from which the AEC samples will be selected when roi_aec_enable is asserted. Configuration is similar to the regular region of interests. The intersection of this window with the active windows define the selected pixels. It is important that this window at least overlaps with one or more active windows. |
同様の部品番号 - PYTHON480 |
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同様の説明 - PYTHON480 |
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